Root length density

Extensive and deep root systems have been recognized as one of the most important traits for improving chickpea (Cicer arietinum L.) productivity under progressively receding soil moisture conditions. However, available information on the range of variation for root traits is still limited. Genetic variability for the root traits was investigated using a cylinder culture system during two consecutive growth seasons in the mini-core germplasm collection of ICRISAT plus several wild relatives of chickpea. The largest genetic variability was observed at 35 days after sowing for root length density (RLD) (heritability, h 2 = 0.51 and 0.54) across seasons, and followed by the ratio of plant dry weight to root length density with h 2 of 0.37 and 0.47 for first and second season, respectively. The root growth of chickpea wild relatives was relatively poor compared to C. arietinum, except in case of C. reticulatum. An outstanding genotype, ICC 8261, which had the largest RLD and one of the deepest root system, was identified in chickpea mini-core germplasm collection. The accession ICC 4958 which was previously characterized as a source for drought avoidance in chickpea was confirmed as one with the most prolific and deep root system, although many superior accessions were also identified. The chickpea landraces collected from the Mediterranean and the west Asian region showed a significantly larger RLD than those from the south Asian region. In addition, the landraces originating from central Asia (former Soviet Union), characterized by arid agro-climatic conditions, also showed relatively larger RLD. As these regions are underrepresented in the chickpea collection, they might be interesting areas for further germplasm exploration to identify new landraces with large RLD. The information on the genetic variability of chickpea root traits provides valuable baseline knowledge for further progress on the selection and breeding for drought avoidance root traits in chickpea.

Soilless plant growth systems are widely used as a means to save irrigation water and to reduce groundwater contamination. While nutrient concentrations in the growth medium are depleted due to uptake by the plants, salinity and toxic substances accumulate due to transpiration. A theoretical model is suggested, to simulate nutrient uptake by plants grown in soilless cultures with recycled solutions. The model accounts for salinity accumulation with time and plant growth, and its effects on uptake of the different nutrients by means of interaction with Na and Cl ions. The sink term occurs due to uptake by a growing root system. Influx as a function of the ion concentration is according to Michaelis-Menten active mechanisms for K + , NO 3 − -N, NH 4 + -N, PO 4 -P, Ca 2+ , Mg 2+ and SO 4 2− , whose influx parameters are affected by Na and Cl − , but not with time (age). Sodium influx is passive above a critical concentration. Sum of cations-anions concentrations is balanced by Cl − to maintain electro-neutrality of the growth solution. Salinity (by means of Na concentration) suppresses root and leaf growth, which further effect uptake and transpiration. The model accounts for instantaneous transpiration losses, during daytime only and its effect on uptake of nutrients and plant development due to salt accumulation. The model was tested against NO 3 − and K + uptake by plants associated with cumulative transpiration and with different NaCl salinity levels. Deviations from observed K + uptake should be attributed to the salinity tolerance of the plants. In a study with data obtained from published literature, the model indicated that nutrient depletion and salinity buildup might be completely different with fully grown-up plants (that do not grow) and plants that grow with time. Depletion of different nutrients are according to their initial concentration and plant uptake rate, but also affected by their interactions with Na and Cl ions.

1) to investigate the spatial distribution of fine roots and its correlation with selected soil properties on an artificial ecosystem dominated by woody vegetation species, and (2) to compare the root distribution to that predicted using a global model for natural ecosystems. Root diameter distribution (≤5 mm), root biomass density (RBD), root length density (RLD), soil pH, soil electrical conductivity and dry soil bulk density were measured on soil core samples (217) collected from a trench wall using a 20×20-cm grid sampling. Approximately 90% of the RBD (mean ± standard error: 0.27±0.027 kg m −3 ) and RLD (1.57±0.023 cm cm −3 ) occurred in the top 40 cm, decreasing exponentially to a maximum rooting depth of 150 cm. RBD exhibited a vertical spatial structure associated with soil pH (p<0.05; r 2 = 0.48), and a random lateral distribution. Coefficients of variation (CV) of RBD were high irrespective of orientation (vertical: 79-200%, lateral: 50-236%). The root extinction parameter β (0.944) for the global model was lower (p<0.05) than that of woodlands (β= 0.964-0.976), indicating a shallow root distribution resembling that of grasslands (β=0.943). The superficial root distribution indicated subsoil chemical constraints to root growth, while high lateral variability was attributed to sparse vegetation. The findings stress the need to account for both vertical and lateral variability of roots for accurate modelling of water use and productivity on certain artificial ecosystems with sparse vegetation.

Wheat (Triticum aestivum L.) is the most important cereal crop after rice in India. Optimum schedule of irrigation for wheat and its response to irrigation based on the ratio of irrigation water and cumulative pan evaporation (irrigation depth (IW):CPE at 1.2, 0.9 and 0.6) was studied in a field experiment during the winter seasons of 1989-1990 and 1990-1991. The site had a sandy loam (Typic Fluvaquent) soil and shallow water table, located in the humid tropical canal command area at the University Experimental Farm, Memari (2381 0 N, 8885 0 E and 21.34 m above mean sea level) in West Bengal, India. The yield of wheat, weekly and seasonal actual evapotranspiration (ETa) from water balance equation, crop coefficients (K c ), soil water stress coefficients (K s ), water extraction patterns, water use efficiency (WUE) and water application efficiency (A e ) were determined. Maximum profile water depletion and ETa of wheat occurred in the wetter moisture regime (1.2 IW:CPE). The average daily ETa varied from <1 mm per day in the early growing period to a maximum value of 2.72 mm per day at 9-14 weeks after sowing (WAS) under 1.2 IW:CPE when leaf area index (LAI) was >3. During crop development to mid season (4-14 WAS), 1.2 IW:CPE showed 9-15% increased ETa than 0.9 and 0.6 IW:CPE. The seasonal ETa of wheat with IW:CPE of 1.2 was 238.2 and 261.95 mm during 1989-1990 and 1990-1991, respectively. Maximum roots were concentrated in the top 150 mm layer (57% of root length density) and maximum root water extraction efficiency (U z ) was observed at 600-750 mm depth under the drier soil moisture regimes of 0.9 and 0.6 IW:CPE, respectively. The yield increased significantly with increasing levels of irrigation. IW:CPE ratio of 1.2 produced 13 and 21% more yield, and 8 and 14% improved WUE than 0.9 and 0.6 IW:CPE, respectively. Water application efficiency (A e ) was noticed higher (79.85%) under 0.6 IW:CPE irrigation regime. Precise information of K c , which is required for regional scale irrigation planning is lacking in developing countries. The estimated values of K c for wheat at four crop growth stages (initial, crop development, mid season and maturity) were 0.33, 0.82, 1.08 and Agricultural Water Management 59 (2003) 33-47 : S 0 3 7 8 -3 7 7 4 ( 0 2 ) 0 0 1 1 2 -9 0.64, respectively which were identical to those suggested by the FAO indicating need for generating these values at the local/regional level. The K s values of 0.6 IW:CPE decreased steeply and experienced more stress condition than 0.9 IW:CPE. #

____________________________________________________________________________________________________________________________________________________________________________ Chopart JL, Sine B, Dao A, Muller B 2008. Root orientation of four sorghum cultivars: application to estimate root length density from root counts in soil profiles. Plant Root 2: 67-75. doi:10.3117/plantroot.2.67 Copyrights 2008, Plant Root (JSRR), www.plantroot.org O Or ri ig gi in na al l r re es se ea ar rc ch h a ar rt ti ic cl le e Abstract:

Traditional vegetative techniques to control gully development rely mainly on the effects of above ground biomass, whereas little attention has been given to the role of below ground biomass. Yet, in a context where above ground biomass may temporarily or spatially disappear (e.g. due to fire or grazing), roots can play an important role in protecting soil against erosion. Few studies have investigated the impacts of roots of natural vegetation (such as grass) on the resistance of topsoils in concentrated flow erosion zones, although grasses grow in many environments. Therefore, the objective of this study is to investigate the impact of root density and root length density of grass on the erodibility of root-permeated saturated topsoils. Three plots were established on a sandy loam. Their treatments were (1) bare, (2) low density drilled grass and (3) high density drilled grass, simulating different root densities. After one month, topsoil samples were taken and subjected to concentrated flow using a hydraulic flume in the laboratory. Slope, flow discharge, mean velocity, water temperature and sediment concentration were measured. Root density and root length density values were assessed. Relative soil detachment rates and mean flow shear stresses were calculated. The results indicate a negative exponential relation between the relative soil detachment rate and root density as well as root length density, independent of the applied flow shear stresses. However, the best relationship fitting the data is the Hill curve, indicating that relative soil detachment rates decrease to very low values (0.05) with an increase in root density from 0 to 4 kg m À 3 or root length density from 0 to 400 km m À 3 . A comparison between the effects of vegetation cover on sheet and rill erosion rates and those of the root area ratio of grass roots on relative soil detachment rates reveals that grass roots are very effective in reducing soil detachment rates. The equations obtained can be used to predict the effect of grass roots on soil erosion rates during concentrated runoff and to evaluate the ability of roots to increase topsoil resistance against erosion by concentrated flow. Calculations of relative erosion rates using the equations from the RUSLE and WEPP models indicate that the observed trend is better predicted with the RUSLE model and the WEPP model for croplands than with the WEPP model for rangelands. D

The potential of Leucaena leucocephala as an erosion control plant was investigated in terms of its capacity of root reinforcement, root profile and root shear strength. The species studied exhibited extensive, dense rooting and depth of penetration. These aspects, to some extent, could provide surficial as well as deep-seated erosion control. A high water absorption capacity would increase suction, thus potentially extracting water at the greater depth. The soil-root matrix significantly affects cohesion factor but not the angle of friction. The effect varies with increasing depth and age of plant depending on the root length density. After 6 months of growth, the cohesion factor had tremendously increased by two-to fivefold (0.1-0.5 m soil depth). This range almost reached the values of those in the 12-month treatment, indicating a high contribution of the root system to soil-root reinforcement.

This review summarises current knowledge on root interactions in agroforestry systems, discussing cases from temperate and tropical ecosystems and drawing on experiences from natural plant communities where data from agroforestry systems are lacking. There is an inherent conflict in agroforestry between expected favourable effects of tree root systems, e.g. on soil fertility and nutrient cycling, and competition between tree and crop roots. Root management attempts to optimise root functions and to stimulate facilitative and complementary interactions. It makes use of the plasticity of root systems to respond to environmental factors, including other root systems, with altered growth and physiology. Root management tools include species selection, spacing, nutrient distribution, and shoot pruning, among others. Root distribution determines potential zones of root interactions in the soil, but are also a result of such interactions. Plants tend to avoid excessive root competition both at the root system level and at the single-root level by spatial segregation. As a consequence, associated plant species develop vertically stratified root systems under certain conditions, leading to complementarity in the use of soil resources. Parameters of root competitiveness, such as root length density, mycorrhization and flexibility in response to water and nutrient patches in the soil, have to be considered for predicting the outcome of interspecific root interactions. The patterns of root activity around individual plants differ between species; knowing these may help to avoid excessive competition and unproductive nutrient losses in agroforestry systems through suitable spacing and fertiliser placement. The possibility of alleviating root competition by supplying limiting growth factors is critically assessed. A wide range of physical, chemical and biological interactions occurs not only in spatial agroforestry, but also in rotational systems. In a final part, the reviewed information is applied to different types of agroforestry systems: associations of trees with annual crops; associations of trees with grasses or perennial fodder and cover crops; associations of different tree and shrub species; and improved fallows.

We studied the effects of applications of traditionally composted farmyard manure (FYM) and two types of biodynamically composted FYM over 9 years on soil chemical properties, microbial biomass and respiration, dehydrogenase and saccharase activities, decomposition rates and root production under grass-clover, activity and biomass of earthworms under wheat, and yields in a grass-clover, potatoes, winter wheat, field beans, spring wheat, winter rye crop rotation. The experiment was conducted near Bonn, on a Fluvisol using a randomised complete block design (n=6). Our results showed that plots which received either prepared or non-prepared FYM (30 Mg ha −1 year −1 ) had significantly increased soil pH, P and K concentrations, microbial biomass, dehydrogenase activity, decomposition (cotton strips), earthworm cast production and altered earthworm community composition than plots without FYM application. Application of FYM did not affect the soil C/N ratio, root length density, saccharase activity, microbial basal respiration, metabolic quotient and crop yields. The biodynamic preparation of FYM with fermented residues of six plant species (6 g Mg −1 FYM) significantly decreased soil microbial basal respiration and metabolic quotient compared to non-prepared FYM or FYM prepared with only Achillea. The biodynamic preparation did not affect soil microbial biomass, dehydrogenase activity and decomposition during 62 days. However, after 100 days, decomposition was significantly faster in plots which received completely prepared FYM than in plots which received no FYM, FYM without preparations or FYM with the Achillea preparation. Furthermore, the application of completely prepared FYM led to signifi-cantly higher biomass and abundance of endogeic or anecic earthworms than in plots where non-prepared FYM was applied.

A survey was conducted on five slopes of differing slope integrity along the North–South Expressway, Malaysia, to study the effects of vegetation on slope stability. Results showed significant effects of vegetation cover on slope stability in two extreme slopes, type A and type E, which represented stable and failed slopes, respectively. The highest root length density (RLD) was observed in type A slope due to the high density of vegetation cover, which eventually resulted in a lower soil water content (SWC). In contrast, the low biomass density of type E slope possessed a low RLD but high SWC, characteristics of a failed slope. Some correlations were also observed: RLD is positively related to shear strength and SWC is negatively related to both soil shear strength and soil penetrability. Thus, the study suggests that SWC and RLD could be used as indicators of slope stability and has the potential to predict slope failure in the future.

Deep and prolific root systems have been associated with enhanced avoidance of terminal drought stress in chickpea. This research evaluated the root traits of 257 recombinant inbred lines (RILs) derived from a cross between a breeding line with a large root system (ICC 4958) and an agronomically preferred variety (Annigeri) to assess the potential for identifying QTL for desirable root traits and to investigate the relationship between root traits, plant growth and seed yield under terminal drought stress. The root traits of field-grown chickpea RILs were measured using the monolith method during the 2001-2002 cropping season, while their shoot biomass and seed yield were evaluated during both 2000-2001 and 2001-2002 seasons. Significant genetic variation was observed amongst the RIL population for root length density, root dry weight and shoot dry weight at 35 days after sowing and for shoot biomass and seed yield at maturity. A linear relationship was observed between root dry weight and shoot dry weight at 35 days after sowing. The overall distribution of root length density and root dry weight among the RILs indicated that these traits are likely to be under polygenic control. The heritability of root dry weight was 0.27 and root length density was 0.23, compared to 0.49 for shoot dry weight at the same stage. The RILs exhibited a range of combinations of root size and seed yield, with a few RILs showing large root systems and high seed yield. However, there was no general correlation between seed yield and root size. High shoot biomass and harvest index contributed to high seed yield of the RILs. The implications for the molecular breeding of drought-avoidance root traits in chickpea are discussed. #

Wheat (Triticum aestivum L.) is the most important cereal crop after rice in India. Optimum schedule of irrigation for wheat and its response to irrigation based on the ratio of irrigation water and cumulative pan evaporation (irrigation depth (IW):CPE at 1.2, 0.9 and 0.6) was studied in a field experiment during the winter seasons of 1989-1990 and 1990-1991. The site had a sandy loam (Typic Fluvaquent) soil and shallow water table, located in the humid tropical canal command area at the University Experimental Farm, Memari (2381 0 N, 8885 0 E and 21.34 m above mean sea level) in West Bengal, India. The yield of wheat, weekly and seasonal actual evapotranspiration (ETa) from water balance equation, crop coefficients (K c ), soil water stress coefficients (K s ), water extraction patterns, water use efficiency (WUE) and water application efficiency (A e ) were determined. Maximum profile water depletion and ETa of wheat occurred in the wetter moisture regime (1.2 IW:CPE). The average daily ETa varied from <1 mm per day in the early growing period to a maximum value of 2.72 mm per day at 9-14 weeks after sowing (WAS) under 1.2 IW:CPE when leaf area index (LAI) was >3. During crop development to mid season (4-14 WAS), 1.2 IW:CPE showed 9-15% increased ETa than 0.9 and 0.6 IW:CPE. The seasonal ETa of wheat with IW:CPE of 1.2 was 238.2 and 261.95 mm during 1989-1990 and 1990-1991, respectively. Maximum roots were concentrated in the top 150 mm layer (57% of root length density) and maximum root water extraction efficiency (U z ) was observed at 600-750 mm depth under the drier soil moisture regimes of 0.9 and 0.6 IW:CPE, respectively. The yield increased significantly with increasing levels of irrigation. IW:CPE ratio of 1.2 produced 13 and 21% more yield, and 8 and 14% improved WUE than 0.9 and 0.6 IW:CPE, respectively. Water application efficiency (A e ) was noticed higher (79.85%) under 0.6 IW:CPE irrigation regime. Precise information of K c , which is required for regional scale irrigation planning is lacking in developing countries. The estimated values of K c for wheat at four crop growth stages (initial, crop development, mid season and maturity) were 0.33, 0.82, 1.08 and Agricultural Water Management 59 (2003) 33-47 : S 0 3 7 8 -3 7 7 4 ( 0 2 ) 0 0 1 1 2 -9 0.64, respectively which were identical to those suggested by the FAO indicating need for generating these values at the local/regional level. The K s values of 0.6 IW:CPE decreased steeply and experienced more stress condition than 0.9 IW:CPE. #

Root length density distribution Normalized root length density distribution Cotton Film mulched drip irrigation Soil water and salinity stresses a b s t r a c t Root length density (RLD) distribution information is essential to crop growth and soil water/solute transport predictions and for rational irrigation scheduling and crop management. Unfortunately, measuring RLD accurately in the field is difficult and time-consuming, especially for row crops such as cotton. Field experiments were conducted over two seasons (Exp. 1 and 2 in 2011 and 2012, respectively) to investigate two-dimensional RLD distribution of cotton under film mulched drip irrigation in Xinjiang, China. Different RLD distributions were created by varying row and drip line spacing, irrigation water salinity, irrigation volume and fertilizer application rate. Both distributions of measured RLD and calculated normalized RLD (NRLD), the root length allocation proportions of a plant at different relative depths, were found to decrease with depth, concentrating within the upper soil layers with nearly negligible differences along the horizontal direction. NRLD values in Exp. 2 were pooled together and simply generalized as a vertical one-dimensional decreasing function with just one fitted coefficient of a = 2.06, which was employed to characterize the maximum value of NRLD at the soil surface and its downward decreasing rate. The generalized function was verified to be in good agreement with the measured NRLD distributions of cotton in Exp. 1, and then further improved using all the NRLD data from Exp. 1 and 2. The improved function (with a = 1.96) was shown useful in estimating RLD distribution and simulating soil water flow and salinity transport in a soil-cotton system.

Rice roots are commonly shallow in rainfed lowland conditions. Mechanical impedance is one factor that may restrict access of roots to deeper soil layers, thereby reducing the capacity of the root system to extract water from depth during late-season drought. The capacity of rice roots to penetrate hardpans was examined in experiments at Rajshahi, Bangladesh, in the 1994 wet season. Eight lines (CT9993, IR52561, IR58821, IR62266, KDML105, Mahsuri, Namsagui19, and IR20) were grown in three experiments: irrigated early, rainfed early, and rainfed late. As drought intensi®ed from heading to dough stage, soil penetration resistance increased to 3.0 MPa at 15±25 cm depth in both rainfed experiments. A high proportion of the total root length was found in the surface layer, particularly in IR20. CT9993 and IR58821 had thicker roots than other lines. Root length density (RLD) increased in deeper soil layers in rainfed with time, but lines differed in their capacity to penetrate the compacted layer as drought intensi®ed after heading. Only IR58821 and Mahsuri were able to increase RLD below 15 cm depth after heading to values greater than 1.6 cm cm À3 , and only in the rainfed early experiment. In rainfed late, soil penetration resistance tended to increase after heading in IR20, IR52561 and IR62266, implying these lines were able to extract water below 15 cm depth, but without the concomitant increase in RLD. The greater penetration ability of Mahsuri and IR58821 was expressed in both rainfed environments at high soil penetration resistance.

Özet: Araştırma dört yıl süreyle Orta Anadolu Bölgesi'nin farklı iklim özelliklerine sahip Haymana-Ankara ve Gözlü-Konya yörelerinde yürütülmüştür. Araştırmanın amacı, kuru tarım alanlarında toprak verimliliğinin artırılması ve nadas alanlarından daha fazla yararlanmaktır. Denemelerde farklı toprak işlemler ile mercimek-buğday ve nadas-buğday ekim nöbeti sistemleri incelenmiştir.

The effect of integrated use of urea and Farm Yard Manure (FYM) on yield and N uptake of wheat was assessed in a field experiment carried out on a silty clay loam soil in Peshawar valley of North West Frontier Province, Pakistan during 2001-02. Urea and FYM were combined in a way to supply N at 120 kg ha -1 from both sources in 0:0, 100:0, 75:25, 50:50, 25:75 and 0:100 ratios arranged in a RCB design with four replications. Wheat (variety: Ghaznavi) was planted in rows. Data on biological, grain and straw yields of wheat were recorded. Samples of grain and straw were also analyzed for total N to determine its uptake by the crop. The results indicated that maximum biological (10952 kg ha -1 ), straw (7710 kg ha -1 ), and grain (3242 kg ha -1 ) yields of wheat were obtained in treatment receiving N from urea and FYM in 75:25 ratio. The next higher yield was obtained in treatment receiving N from the two sources in 50:50 ratio. Comparing with other fertilizer treatments, the yields were significantly lower in treatments where N from urea source was below 50 %. Similarly, the N uptake in grain (47.66 kg ha -1 ) and straw (19.28 kg ha -1 ) was also significantly (P<0.05) greater in treatments receiving 75 or 50 % N from urea and 25 or 50% from FYM. The data on crop yields and N uptake in response to integrated use of urea and FYM supported each other. The residual soil organic fertility after crop harvest was proportional to the level of FYM used. Our data thus suggest that integrated use of urea and FYM at 75:25 or 50:50 ratios (N basis) has produced maximum yields and is therefore recommended for profitable wheat yield and sustainable soil fertility.

Tree root systems may improve soil fertility through carbon inputs, uptake of leachable nutrients and maintenance of soil biomass, but can at the same time reduce crop yields by competition for water and nutrients. Quantitative information about the positive and negative effects of tree roots and their changes in space and time are necessary for the optimization of agroforestry associations. An alley cropping experiment was layed out as a randomized complete block design on a Plinthic Lixisol/Ferralic Cambisol with Gliricidia sepium hedgerows at 5 m distance, including a sole cropping control. The development of root systems was monitored by sequential soil coring (eight samplings) during one year, with maize and groundnut as crops. Additional information is presented from a single sampling for rice during the foregoing year. Pronounced fluctuations of live root length density indicated an important variability in the nutrient and water uptake capacity of the vegetation. At low total root length density, the hedgerows affected the root development in the agroforestry plots directly by the presence of their root systems. At high root length density, they affected root development mainly by improving crop root growth and influencing the composition of the spontaneous vegetation. The root length density of the hedgerows was too low to compete with the crops for soil resources. The hedgerows tended to increase root length densities in the subsoil when few roots were present, thus possibly reducing the risk of nutrient leaching. However, the length density of the perennial root systems decreased during the cropping season, presumably as an effect of repeated pruning, and attained minimum values almost at the same time as the crops. Trees with denser root systems which are less frequently pruned may be more efficient in achieving closer nutrient cycles, though at the cost of higher root competition with crops.

The study attempts to quantify the root biomass and density, nodulation, crop biomass and grain yield of soybean, to analyze crop growth and energy (renewable and nonrenewable) inputs in relation to fertilizer-NPK and organic manure. Observations were recorded from soybean grown with no fertilizer, NPK and NPK þ FYM (farmyard manure). The root biomass (BM root) increased significantly with NPK þ FYM compared to NPK and control. The trend of BM root was best fitted with a third order polynomial. Root length density was higher in NPK þ FYM. Biomass of stem, petiole and leaf were significantly greater in NPK þ FYM than other treatments, relative contribution to total biomass at physiological maturity were stem 29%, petiole 9%, leaf 17% and pod 46%; quadratic regression models best represented the stem, petiole and leaf biomass data. A maximum LAI of 4.88, total biomass of 633 g m À2 at maturity, CGR of 18.4 g m À2 d À1 were recorded in NPK þ FYM. Grain yields increased by 72.5 and 98.5%, and stover yields by 56.0 and 94.8% in NPK and NPK þ FYM, respectively over control. Though the total energy input in NPK þ FYM was greater than those in NPK and control, the share of renewable energy was much higher with greater net energy output and non-renewable energy productivity in NPK þ FYM than NPK. The use efficiency of non-renewable energy was also higher in NPF þ FYM. Thus, a combination of NPK-fertilizer and organic manure (FYM) could be the viable nutrient management option for soybean production.

study the effect of combinations of amount of irrigation water and nutrient applications on crop growth, evapotranspiration (ET), yield and water use efficiency (WUE) of Indian mustard on a heavy clay soil in central India. Three irrigation regimes, viz. 60 mm presowing and no post-sowing irrigation (I 60), 60 mm pre-sowing plus 60 mm post-sowing irrigation at flowering (I 120), and 60 mm pre-sowing plus 60 mm post-sowing irrigation at rosette and at flowering stage (I 180); and three nutrient application treatments, viz. no fertilizer/manure (F 0), 100% NPK, i.e., total N, P and K rates of 60, 13.1 and 16.6 kg ha À1 , respectively (F 100) and 100% NPK plus 10 Mg ha À1 farmyard manure (F 100 M 10) were tested in a split-plot design. The experiment was conducted for three consecutive seasons. The results revealed that treatment combinations of I 180 Â F 100 M 10 , I 120 Â F 100 M 10 and I 180 Â F 100 maintained significantly greater leaf area index (LAI), above-ground dry matter (DM), ET, seed and biomass yield of the crop than other combinations. The duration of a LAI of !2.5 was more in F 100 and F 100 M 10 than in F 0. Under I 120 , LAI remained !2.5 for 8 and 22 days in F 100 and F 100 M 10 , respectively. This leaf area duration increased to 28 and 39 days in the corresponding nutrient treatments under I 180. The root length, mass and volume densities were significantly higher in I 180 than I 120 and I 60 , and in F 100 M 10 than F 100 and F 0. For a particular irrigation regime, ET increased significantly in F 100 and F 100 M 10 compared to F 0. The maximum seed yield of 1736 kg ha À1 was recorded in I 180 Â F 100 M 10 ; and the seed yields under I 120 Â F 100 M 10 (1440 kg ha À1) and I 180 Â F 100 (1431 kg ha À1) did not vary significantly. The WUE seed and WUE biomass decreased with the increase in amount of irrigation water. On the contrary, these WUE parameters increased in F 100 and F 100 M 10 compared to F 0. The regression relationships of root length density on ET, and yield (both seed and biomass yield) on ET could be described by linear. Thus, I 180 Â F 100 M 10 is the best combination; and as the crop response to I 120 Â F 100 M 10 and I 180 Â F 100 was similar, this study concludes that application of organic manure along with 100% NPK fertilizers could reduce the need for one post-sowing irrigation without compromising the yield of this crop under deficit irrigation.

In As-and metal-contaminated pyrite wastes, contaminant stripping is not feasible, and root foraging and quantification of root dynamics holds the key to stabilisation in woody species. a b s t r a c t At a site in Udine, Italy, a 0.7 m layer of As, Co, Cu, Pb and Zn contaminated wastes derived from mineral roasting for sulphur extraction had been covered with an unpolluted 0.15 m layer of gravelly soil. This study investigates whether woody biomass phytoremediation is a realistic management option. Comparing ploughing and subsoiling (0.35 m depth), the growth of Populus and Salix and trace element uptake were investigated in both pot and field trials. Species differences were marginal and species selection was not critical. Impaired above-ground productivity and low translocation of trace elements showed that bioavailable contaminant stripping was not feasible. The most significant finding was of coarse and fine roots proliferation in surface layers that provided a significant sink for trace elements. We conclude that phytostabilisation and effective immobilisation of metals and As could be achieved at the site by soil amelioration combined with woody species establishment. Confidence to achieve a long-term and sustainable remediation requires a more complete quantification of root dynamics and a better understanding of rhizosphere processes.

The concept of competition or complementarity between tree and crop roots for below ground resources have been a major debate in simultaneous systems. Root studies were conducted in three cropping systems, namely: sole maize, pigeon pea/maize intercropping and Gliricidia sepium (Gliricidia)/maize intercropping, with the objective of understanding the potential for competition or otherwise. Pigeon pea and maize root development was monitored at 21, 42 and 63 days after planting (DAP). Also soil mineral N and Olsen P were assessed along the soil profile up to 200 cm depth. Maize roots developed faster than those of pigeon pea during the first 42 days after planting and there was little overlapping of maize and pigeon pea roots. However, the roots of both pigeon pea and maize had its peaks at 63 DAP, suggesting potential competition during reproductive growth stage of maize. In Gliricidia/maize intercropping, maize had the highest root density averaging 1.02 cm cm -3 in the top 0 -4 0 cm soil layer, whereas gliricidia had lower root length density (0.38 cm cm -3 ) in the top 0 -40 cm soil layer compared to 0.65 cm cm -3 in the subsoil (40 -100 cm). In Gliricidia/maize intercropping, mineral N was increased by 34 -44 kg ha -1 in the 0 -100 cm soil layer, whereas Olsen P decreased by 32 kg ha -1 in the entire 0-200 cm soil profile compared to the sole maize plot. Pigeon pea may be the "loser" in an association that involved both maize and Gliricidia. Because maize had more roots growing within 0 -40 cm soil layer than Gliricidia it is able to take advantage of the nutrients from the applied Gliricidia prunings in the ridges. The study confirmed root compatibility between Gliricidia and maize and nutrient pumping from deep soil layers.

Understanding and predicting the responses of plant communities to multiple overlapping disturbances remains a challenging task. Hurricane Wilma represents a large, yet infrequent type of disturbance that was superimposed on an existing disturbance gradient of time since fire. We examined disturbance and recovery patterns in response to these overlapping disturbances by measuring how canopy structure, fine roots, mycorrhizae, and soil nitrogen dynamics, varied along a fire chronosequence in the 2 years after Hurricane Wilma. Hurricane damage increased canopy openness in all seral stages. In the early-seral stage, canopy openness returned to prehurricane conditions within 2 years, whereas canopy openness in the late-seral stage remained significantly higher throughout the study. We observed no significant change in root length density in the early-and mid-seral stages. However, in the late-seral stage, root length density was significantly reduced immediately after the hurricane and remained so 2 years after the hurricane. In the late-seral stage, we also observed a significant reduction in percent soil nitrogen and a significant increase in soil nitrogen isotopic composition (d 15 N) values, indicating a loss of soil nitrogen. In contrast, in the early-and midseral stages, there were no significant changes in percent nitrogen or soil d 15 N values. Results from this study suggest that forest fire disturbance history influences responses to hurricane damage. Moreover, feedbacks between aboveground and belowground processes have the potential to influence forest recovery.

Root growth at soil depths below 30 cm may provide access to critical soil water reserves during drought in rainfed lowland rice. In this study, the OryzaSNP panel, a set of 20 lines representing genetic diversity in rice used for the discovery of DNA sequence polymorphisms, was evaluated for root characteristics in the field over three seasons varying in drought severity. Root length density (RLD) at a depth of 30-45 cm varied up to 74-92% among genotypes under drought stress (2008-2009 dry seasons), ranging from 0.024 to 0.23 cm cm −3 in 2008 and from 0.19 to 0.81 cm cm −3 in 2009. Real-time monitoring of soil moisture profiles revealed significant differences among genotypes, and these differences were correlated with RLD at those soil depths. Among the lines evaluated, the Aus isozyme group, particularly the genotype Dular, showed greater drought resistance associated with deep root growth and the highest drought response index (less reduction in yield by drought stress). Since the set of genotypes used in this study has been completely sequenced for SNP markers, the phenotypic information on root growth and drought avoidance responses presented here could be used in initial analysis of the genetic basis of dehydration avoidance traits and in facilitating improvement in drought resistance in rice.

Biological scientists are increasingly addressing the interactions of genetic potential and environmental influences (GxE interaction) to understand the mechanisms for resulting phenotypic expression of such potential. This body of epigenetic knowledge has focused on the level of molecular biology but needs now to deal more with interactions at the level of organisms, e.g. plants and microbes that affect each other's development and performance. The System of Rice Intensification (SRI) which originated in Madagascar in the 1980s shows how by altering age-old management practices for plants, soil, water and nutrients, rice genotypes can produce dramatically more productive plant phenotypes. These yield more grain with less input of seeds, water, fertilizer and even labour. The practices in particular produce much larger and longer-lived root systems, and these are associated with increased and modified populations of soil biota. This paper summarizes what is known about these dynamics from field studies and experimental data.

Previous studies relating root systems and drought tolerance in oil palm focused mainly on biomass. Yet, total root length (TRL), total root surface area (TRS), and root distribution in the soil better determine water uptake. These morphological traits were studied on 3 oil palm genotypes displaying a contrasting drought tolerance. A new concept of potential root water extraction ratio (PRER)

Solanum sisymbriifolium is a trap crop for potato cyst nematodes (PCN). In this study, we quantified the effect of different periods of growth of S. sisymbriifolium and root length density on hatching of Globodera pallida, using potato and fallow treatments as references. One-year-old and 2-year-old G. pallida cysts were used in greenhouse experiments carried out in containers over 2 years. Two methods were used in study hatching. In the first method, 7.5-cm-diameter soil cores were removed and backfilled with infested soil. In the second method, cysts were buried in nylon bags. The soil cores infested with cysts used in the first method had very poor root colonisation as compared to surrounding bulk soil. Therefore, the effect of S. sisymbriifolium was strongly underestimated by the soil core method. Hatching of PCN juveniles from cysts, measured with the nylon bag method, increased with the duration of growth of S. sisymbriifolium from 47% after 6 weeks of crop growth up to 75% after 21 weeks of crop growth. Reductions per depth layer were also correlated with root length density and varied between 42.6% at 0.26 cm cm 23 and 85.3% at 5.8 cm cm 23. Based on a single exponential decay function, a general method is presented to estimate for any PCN management measure the average reduction in the number of years needed to ensure that the PCN population falls below a given density. Calculated reductions in the number of years ranged from 2.3 years for 59% hatching (equivalent to 90 days of S. sisymbriifolium) to 4.4 years for 75% of hatching (equivalent to 150 days of S. sisymbriifolium). These reductions were independent of initial and final population density. Our results corroborate the hatchinducing effect of S. sisymbriifolium, underline the importance of growth duration and root length density as determinants of the reduction in PCN population that can be achieved and draw attention to the pitfall in methodology that can arise in the study of hatch stimulation.

Most trickle irrigation in the world is surface drip yet subsurface drip irrigation (SDI) can substantially improve irrigation water use efficiency (IWUE) by minimizing evaporative loss and maximizing capture of in-season rainfall by the soil profile. However, SDI emitters are placed at depths, and in many soil types sustained wetting fronts are created that lead to hypoxia of the rhizosphere, which is detrimental to effective plant functioning. Oxygation (aerated irrigation water) can ameliorate hypoxia of SDI crops and realize the full benefit of SDI systems. Oxygation effects on yield, WUE and rooting patterns of soybean, chickpeas, and pumpkin in glasshouse and field trials with SDI at different emitter depths (5, 15, 25, and 35 cm) were evaluated. The effect of oxygation was prominent with increasing emitter depths due to the alleviation of hypoxia. The effect of oxygation on yield in the shallow-rooted crop vegetable soybean was greatest (+43%), and moderate on medium (chickpea +11%) and deep-rooted crops (pumpkin +15%). Oxygation invariably increased season-long WUE (WUEsl) for fruit and biomass yield and instantaneous leaf transpiration rate. In general, the beneficial effects of oxygation at greater SDI depth on a heavy clay soil were mediated through greater root activity, as observed by general increase in root weight, root length density, and soil respiration in the trialed species. Our data show increased moisture content at depth with a lower soil oxygen concentration causing hypoxia. Oxygation offsets to a degree the negative effect of deep emitter placement on yield and WUE of SDI crops.

Studies on soil strength and rooting characteristics of crops are important for water and nutrient budgeting and also for deciding the adoption of suitable soil management practice for sustainable crop production. In the present field trial, the variation of soil penetration resistance (PR) with soil water content (SWC (w/w)) and bulk density (BD) changes under bed and conventionally planted wheat was studied on a sandy loam soil of research farm of Indian Agricultural Research Institute, New Delhi. The differences in root characteristics of both systems were also compared. The results showed that, in general for all SWC, with increase in BD from 1.2 to 1.6 Mg m − 3 , PR increased but the increase was more sharp in conventional than in bed planting system. It was further seen that, at all BDs, the critical soil strength of 2 MPa arrived at higher SWC in conventional as compared to bed planting. It thus indicated that root growth continued normally at relative lower SWC in bed planting as compared to conventional planting.

This literature review presents information about the role of tree root systems for the functioning of agroforestry associations and rotations and attempts to identify root-related criteria for the selection of agroforestry tree species and the design of agroforestry systems. Tree roots are expected to enrich soil with organic matter, feed soil biomass, reduce nutrient leaching, recycle nutrients from the subsoil below the crop rooting zone and improve soil physical properties, among other functions. On the other hand, they can depress crop yields in tree-crop associations through root competition. After a brief review of favourable tree root effects in agroforestry, four strategies are discussed as potential solutions to the dilemma of the simultaneous occurrence of desirable and undesirable tree root functions: 1) the selection of tree species with low root competitiveness, eventually supplemented by shoot pruning; 2) the identification of trees with a root distribution complementary to that of the crops; 3) the reduction of tree root length density by trenching or tillage; and 4) the use of agroforestry rotations instead of tree-crop associations. The potential and limitations of these strategies are discussed, and deficits in current understanding of tree root ecology in agroforestry are identified. In addition to the selection of tree species and provenances according to root-related criteria, the development of management techniques that allow the manipulation of tree root systems to maximize benefit and minimize competition are proposed as important tasks for future agroforestry research.

Deep and prolific root systems have been associated with enhanced avoidance of terminal drought stress in chickpea. This research evaluated the root traits of 257 recombinant inbred lines (RILs) derived from a cross between a breeding line with a large root system (ICC 4958) and an agronomically preferred variety (Annigeri) to assess the potential for identifying QTL for desirable root traits and to investigate the relationship between root traits, plant growth and seed yield under terminal drought stress. The root traits of field-grown chickpea RILs were measured using the monolith method during the 2001-2002 cropping season, while their shoot biomass and seed yield were evaluated during both 2000-2001 and 2001-2002 seasons. Significant genetic variation was observed amongst the RIL population for root length density, root dry weight and shoot dry weight at 35 days after sowing and for shoot biomass and seed yield at maturity. A linear relationship was observed between root dry weight and shoot dry weight at 35 days after sowing. The overall distribution of root length density and root dry weight among the RILs indicated that these traits are likely to be under polygenic control. The heritability of root dry weight was 0.27 and root length density was 0.23, compared to 0.49 for shoot dry weight at the same stage. The RILs exhibited a range of combinations of root size and seed yield, with a few RILs showing large root systems and high seed yield. However, there was no general correlation between seed yield and root size. High shoot biomass and harvest index contributed to high seed yield of the RILs. The implications for the molecular breeding of drought-avoidance root traits in chickpea are discussed.

Crop yields can be reduced by soil compaction due to increased resistance to root growth, and decrease in water and nutrient use efficiencies. A field experiment was conducted during 1997-1998 and 1998-1999 on a sandy clay loam (fine-loamy, mixed, hyperthermic Typic Haplargids, USDA; Luvic Yermosol, FAO) to study subsoil compaction effects on root growth, nutrient uptake and chemical composition of wheat (Triticum aestivum L.) and sorghum (Sorghum bicolor L. Moench). Soil compaction was artificially created once at the start of the study. The 0.00-0.15 m soil was manually removed with a spade. The exposed layer was compacted with a mechanical compactor from 1.65 Mg m À3 (control plot) to a bulk density of 1.93 Mg m À3 (compacted plot). The topsoil was then again replaced above the compacted subsoil and levelled. Both compacted and control plots were hoed manually and levelled. Root length density, measured at flowering stage, decreased markedly with compaction during 1997-1998 but there was little effect during 1998-1999. The reduction in nutrient uptake by wheat due to compaction of the subsoil was 12-35% for N, 17-27% for P and up to 24% for K. The reduction in nutrient uptake in sorghum due to subsoil compaction was 23% for N, 16% for P, and 12% for K. Subsoil compaction increased N content in wheat grains in 1997-1998, but there was no effect on P and K contents of grains and N and P content of wheat straw or sorghum stover. During 1997-1998, K content of wheat straw was statistically higher in control treatment compared with compacted treatment. In 1998, P-content of sorghum leaves was higher in compacted treatment than uncompacted control. Root length density of wheat below 0.15 m depth was significantly reduced and was significantly and negatively correlated with soil bulk density. Therefore, appropriate measures such as periodic chiselling, controlled traffic, conservation tillage, and incorporating of crops with deep tap root system in rotation cycle is necessary to minimize the risks of subsoil compaction. #

We evaluated the validity of predawn leaf water potential (c PL ) as an irrigation-timing indicator, using five field-grown wheat cultivars in three moisture regimes in northern Syria. The relationships between c PL and amount of roots, soil water potential (c Soil ), and vapor pressure deficit (VPD) were examined. The effect of the amount of roots on c PL was only observed before the onset of tillering. The effect of c Soil was recognized for values below the primary wilting point, and a relationship between nighttime VPD and c PL was observed above the primary wilting point in some cultivars. However, grain yield decline in the 50% irrigation treatment was not explained by the c PL change; therefore, the use of c PL alone is not recommended for determining irrigation timing in the study area. #

Over the last decade, bamboo plantations have started to be used as vegetation filters for wastewater treatment. This treatment system can be useful in reducing wastewater discharge into the environment, thus contributing to the preservation of water resources by using the plantation's evapotranspiration to reduce the rate of water infiltration. The evapotranspiration rates of the bamboo species used is therefore an important factor. The actual evapotranspiration (ET) and the crop coefficients (k c ) for the five tropical and temperate species of three-year-old bamboo plants, i.e. Bambusa oldhamii, Bambusa multiplex, Bambusa vulgaris, Phyllostachys aurea and Pseudosasa japonica, were studied in lysimeters for a period of more than one year under a tropical climate. The average ET rates for the bamboo species studied ranged from 4 to 7 mm day −1 with maximum values of between 10.7 and 17.1 mm day −1 during the wet season, and an average k c of 1.1 to 1.9. The ET was correlated to weather parameters, especially minimum temperatures. The differences in ET rates between the bamboo species can be explained by morphological parameters, in particular the total aboveground biomass. Among the five bamboo species studied, B. oldhamii had the highest ET rate and produced the most biomass. In comparison with other high-biomass-producing plants, the evaporation rates for young bamboo plants were similar to those for willow and poplar vegetation filters.

The information of soil compaction effects on growth and yield of crops for saline and waterlogged soils is scanty. A pot experiment was conducted on a sandy clay loam soil during 2001-2002 to study the interactive effects of soil compaction, salinity and waterlogging on grain yield and yield components of two wheat (Triticum aestivum) genotypes (Aqaab and MH-97). Compaction was achieved at 10% moisture level by dropping 5 kg weight, controlled by a tripod stand for 20 times from 0.6 m height on a wooden block placed inside the soil filled pots. Soil bulk density of non-compact and compact treatments was measured as 1.21 and 1.65 Mg m −3 , respectively. The desired salinity level (15 dS m −1 ) was developed by mixing the required amount of NaCl in soil before filling the pots. Waterlogging was developed by flooding the pots for 21 days both at tillering and booting stages. Compaction aggravated the adverse effect of salinity on grain yield and different yield components of both the wheat genotypes. Average reduction in grain yield was 44% under non-compact saline conditions against 76% under compact saline conditions. Similarly, the reduction was about 20% more for 100 grain weight and shoot length, 30% more for number of spikelets per spike, 37% more for number of tillers per plant, and 32% more for straw weight in compact saline treatment than in non-compact saline treatment. Compaction alone caused a reduction of 36% in grain yield. The effect of waterlogging on grain yield and yield components was mostly not changed significantly due to compaction. Rather waterlogging mitigated the effect of compaction for most of the yield components except for number of spikes per plant. Therefore, as for normal soils, the cultivation of salt-affected soils should employ implements and techniques which minimize compaction of root zone soil. The effect of soil compaction can also be minimized by light irrigations with short intervals and by using a stress tolerant crop genotype.

Correct modeling of root water uptake partitioning over depth is an important issue in hydrological and crop growth models. Recently a physically based model to describe root water uptake was developed at single root scale and upscaled to the root system scale considering a homogeneous distribution of roots per soil layer. Root water uptake partitioning is calculated over soil layers or compartments as a function of respective soil hydraulic conditions, specifically the soil matric flux potential, root characteristics and a root system efficiency factor to compensate for within-layer root system heterogeneities. The performance of this model was tested in an experiment performed in two-compartment split-pot lysimeters with sorghum plants. The compartments were submitted to different irrigation cycles resulting in contrasting water contents over time. The root system efficiency factor was determined to be about 0.05. Release of water from roots to soil was predicted and observed on several occasions during the experiment; however, model predictions suggested root water release to occur more often and at a higher rate than observed. This may be due to not considering internal root system resistances, thus overestimating the ease with which roots can act as conductors of water. Excluding these erroneous predictions from the dataset, statistical indices show model performance to be of good quality.

A model has been used to simulate potassium (K) uptake by wheat in a pot culture experiment. Three soils from India, namely Alfisol, Inceptisol and Vertisol, were differentially K exhausted by Sudan grass (Surghum vulgare var. Sudanensis) for a period of 280 days and were used to simulate potassium uptake by wheat (Triticum aestivum) and also to predict the amounts of K released or fixed during cropping. Except in Alfisol all the predicted values of K uptake closely agreed with that of measured values. When predicted K uptake values were plotted against the observed values, r 2 values were found to be 0.927, 0.828 and 0.721 in Inceptisol, Alfisol, and Vertisol, respectively. There is a close relationship between observed and predicted values of K uptake as evident from the high r 2 values, but in case of Alfisol and Vertisol the model has over-predicted K uptake, which perhaps was due to over prediction of K release from non-exchangeable form. The model has been validated and has been applied to simulate response towards fertilizer application at different available K. It was showing that maximum response occurs at a particular value of available K, which shifts towards higher value as release threshold level (RTL) increases. Predicted K uptake was most sensitive to changes in root parameters such as root length density (RLD) and maximum influx rate (V max ), since changes in the time at which maximum root length density was attained (RLD-B) and the decay constant of V max (V max -B) gave the greatest changes in K uptake in almost all the soils except highly exhausted Alfisol in which predicted potassium uptake was more sensitive to changes in RLD-B and intercept (c) than to 2 root uptake kinetics, as described by Michaelis-Menten constant (K m ) and V max . The predicted potassium uptake was least sensitive to changes in rate constants of release and fixation and fixation threshold level in Inceptisol and Vertisol, but was sensitive to release threshold level and rate constant of release in Alfisol.

Yield and water productivity of potatoes grown in 4.32m2 lysimeters were measured in coarse sand, loamy sand, and sandy loam and imposed to full (FI), deficit (DI), and partial root-zone drying (PRD) irrigation strategies. PRD and DI as water-saving irrigation treatments received 65% of FI after tuber bulking and lasted for 6 weeks until final harvest. Analysis across the soil

Most trickle irrigation in the world is surface drip yet subsurface drip irrigation (SDI) can substantially improve irrigation water use eYciency (IWUE) by minimizing evaporative loss and maximizing capture of in-season rainfall by the soil proWle. However, SDI emitters are placed at depths, and in many soil types sustained wetting fronts are created that lead to hypoxia of the rhizosphere, which is detrimental to eVective plant functioning. Oxygation (aerated irrigation water) can ameliorate hypoxia of SDI crops and realize the full beneWt of SDI systems. Oxygation eVects on yield, WUE and rooting patterns of soybean, chickpeas, and pumpkin in glasshouse and Weld trials with SDI at diVerent emitter depths (5, 15, 25, and 35 cm) were evaluated. The eVect of oxygation was prominent with increasing emitter depths due to the alleviation of hypoxia. The eVect of oxygation on yield in the shallow-rooted crop vegetable soybean was greatest (+43%), and moderate on medium (chickpea +11%) and deep-rooted crops (pumpkin +15%). Oxygation invariably increased season-long WUE (WUE sl ) for fruit and biomass yield and instantaneous leaf transpiration rate. In general, the beneWcial eVects of oxygation at greater SDI depth on a heavy clay soil were mediated through greater root activity, as observed by general increase in root weight, root length density, and soil respiration in the trialed species. Our data show increased moisture content at depth with a lower soil oxygen concentration causing hypoxia. Oxygation oVsets to a degree the negative eVect of deep emitter placement on yield and WUE of SDI crops.