Papers by Pardon Muchaonyerwa
Journal of Environmental Quality
Biogas slurry has potential as an organic nutrient source, and understanding its effect on carbon... more Biogas slurry has potential as an organic nutrient source, and understanding its effect on carbon (C) exchange in soils is important for clarifying the contribution of organic amendments to soil fertility and the C budget globally. This study evaluated the effect of biogas slurry (BGS), cattle manure (CM) and chemical fertilizer (CF) on carbon dioxide (CO2) fluxes, microbial biomass C and β-glucosidase activity during the 2016/2017 and 2017/2018 maize seasons, covering December to May, in South Africa. The experiment was arranged in a randomized complete block design with the treatments as (i) BGS, (ii) CM and (iii) CF, applied at 40, 80 and 120 kg N ha-1. In both seasons, BGS and CM had higher CO2 fluxes than CF. Relative to CM, BGS resulted in higher CO2 flux earlier in the season and lower at later stages. The highest CO2 flux was in February but decreased as the season progressed. When expressed as a percentage of organic C present, CO2 fluxes increased with N rate for CM, decreased for BGS and minimally changed for CF. At maize harvest the microbial biomass C and β-glucosidase activity were higher in CM than BGS at all N levels tested. These findings imply that application of BGS and CM increase CO2 fluxes, soil organic C, microbial biomass C and β-glucosidase activity, relative to CF, and the two organic resources also differ in their contribution depending on the part of the season, at least in the short term. This article is protected by copyright. All rights reserved.
Journal of Soil Science and Plant Nutrition, 2022
Changes in soil organic carbon (SOC) and aggregate stability as a result of agricultural practice... more Changes in soil organic carbon (SOC) and aggregate stability as a result of agricultural practices have been extensively studied, but the extent of these changes is site and crop specific. In this study, SOC and aggregate stability were evaluated under undisturbed grassland, cultivated pasture and arable land uses in northern KwaZulu-Natal, South Africa. The soils in this study were sampled from the 0–5, 5–10 and 10–20 cm depths of a Nitisol, Stagnosol and Fluvisol, and analysed for SOC content and stocks and aggregate stability. In all soils, SOC was significantly lower under arable cultivation (range from 1.4 to 2.1%) compared to the grassland and pasture (3.4 to 4.2%) in the top 10 cm. The soil carbon stocks followed a similar trend to the SOC in all soils and under all land uses. The overall aggregate stability expressed as mean weight diameter (MWD) was also significantly lower under the arable land use (1.03 to 1.82 mm) compared to grassland (2.44 to 2.96 mm) at all depths in ...
Soil Research, 2019
Knowledge gaps exist in the literature regarding inclusion of reserve-potassium (K) and K fixatio... more Knowledge gaps exist in the literature regarding inclusion of reserve-potassium (K) and K fixation when formulating K fertiliser requirements for sugarcane. This study investigated the levels of reserve-K and K fixation in the soils of the South African sugar industry, as well as their potential impacts on K requirements for crop growth. The investigation involved 113 topsoil (0–20cm) samples, which included Acrisols, Arenosols, Ferralsols, Fluvisols, Leptosols, Luvisols, Nitisols, Plinthisols, and Vertisols. The release of K from the non-exchangeable reserves was measured using 1.0M boiling HNO3 minus exchangeable K, and was termed reserve-K. The capacity of the soil to fix added K was estimated through medium-term incubations and termed the K requirement factor (KRF, the amount of fertiliser K required to raise exchangeable K by a single unit). Both reserve-K and KRF varied widely across all soils and within soil types. Furthermore, there were also wide variations in the relations...
Environmental Monitoring and Assessment, 2017
Disposal of hair wastes at landfills causes nitrate leaching to ground water, and use of the wast... more Disposal of hair wastes at landfills causes nitrate leaching to ground water, and use of the waste as fertiliser could be a viable option. This study was to determine elemental composition of major hair types in South Africa and their nitrogen (N) and phosphorus (P) release in soil. Wastes of African, White and Indian hair were obtained from local salons and analysed for carbon (C), N and sulphur (S) with the Leco CNS analyzer, and P, bases, aluminium (Al) and micronutrients, with the ICP. We also conducted an incubation study to determine changes in mineral N and P in soil. Hair wastes were added to soil at increasing rates based on N, incubated at 25°C with destructive sampling after 0, 28, 56 and 84 days and pH, ammonium-N, nitrate-N and extractable P measured. All data were subjected to analysis of variance. Indian and White hair had higher N than African. White hair had higher C and lower potassium (K) than those of other types. The Fe levels in hair were in the order White > African > Indian, whilst those of Al were African > Indian > White. African hair had higher calcium (Ca), manganese (Mn), zinc (Zn) and cobalt (Co) than the other types. Ammonium-N and nitrate-N releases were in the order: Indian > African > White, especially at higher rates. Ammonium-N increased in the first 28 days and declined thereafter, when nitrate-N increased and pH decreased. The findings implied that hair types differ in elemental composition and nitrogen release in soil, with implications on pollution and soil fertility.
Land
Disposal of potato waste at landfills results in nutrient losses and pollution of air and groundw... more Disposal of potato waste at landfills results in nutrient losses and pollution of air and groundwater. Biochar from the waste could minimise carbon dioxide (CO2) emission, increase storage of carbon (OC) and recycle nutrients in soil. This study determined effects of biochar from cull potato (CP) and pine bark (PB) on CO2 emission and available nitrogen (N), phosphorus (P), and potassium (K) in contrasting soils. Biochar pyrolysed at 350 °C (CP350; PB350) and 650 °C (CP650; PB650), and feedstocks were applied to Luvisol and Ferralsol soils at rates equivalent to 10 Mg C ha−1 and incubated at 25 °C. The carbon dioxide (CO2-C) was captured in 1 M NaOH and the solution was back-titrated with 0.5 M HCl after 3, 7, 14, 21, 28, 42, 56, and 84 days. A similar experiment was conducted, with destructive sampling, including after 112 and 140 days, for analysis of ammonium-N, nitrate-N, and available P and K. Biochar increased CO2 in the Luvisol but decreased it in the Ferralsol when compared ...
Heliyon, 2018
In organic soil fertility management, rock phosphate (RP) is gaining momentum as an acceptable ph... more In organic soil fertility management, rock phosphate (RP) is gaining momentum as an acceptable phosphorus source, though much of this P is not bioavailable for plant uptake, particularly in igneous RP. This study evaluated the nutrient solubilization, biodegradation and heavy metal concentration when cow dung - waste paper mixture amended with increasing rates of igneous RP was vermicomposted with . The cow dung was optimized to a C/N ratio of 30 using waste paper and amended with RP to provide 0%; 2%; 4% and 8% of elemental phosphorus on a dry w/w basis. Incorporation of RP at 2% and 8% P enhanced compost biodegradation resulting in a 12% and 22% significantly ( < 0.001) lower final C/N ratio, respectively, compared to the control; together with higher humification parameters. Amending the cow dung - waste paper mixture with 2%, 4% and 8% P as rock phosphate, resulted in a 39%; 50% and 65% more resin extractable P, respectively, relative to the control. Similarly, the bicarbonat...
South African Journal of Plant and Soil, 2018
Sustainable management of soils requires knowledge of the impact of agronomic practices such as t... more Sustainable management of soils requires knowledge of the impact of agronomic practices such as tillage and crop rotation on soil quality. The objective of this study was to identify soil chemical and biological soil attributes with high sensitivity to tillage and rotational cover cropping practices on two sandy clay loam soils, a Bonheim at Burnshill and a Shortlands at Lenye, in the Zanyokwe Irrigation Scheme, Eastern Cape, South Africa. Treatments were no tillage, conventional tillage and three crop rotations involving maize-fallow-maize, maize-wheat-maize and maize-oatmaize. Principal component analysis was used to isolate the soil chemical and biological parameters that were most altered by tillage and crop rotations, while hierarchical cluster analysis was used to discriminate the crop rotation effects. Results showed that soil microbial biomass nitrogen, mineralisable nitrogen, and extractable phosphorus were the properties most altered by tillage and crop rotations. The soil properties that were most sensitive to tillage and crop rotations were those most influenced by organic matter inputs. The maize-wheat-maize and maize-oatmaize rotations were clustered together, indicating the similarity of their positive impact on soil quality.
South African Journal of Science, 2017
South Africa currently faces a wheat (Triticum aestivum L.) crisis as production has declined sig... more South Africa currently faces a wheat (Triticum aestivum L.) crisis as production has declined significantly over the past few years. The objective of this study was to explore opportunities for improving yields in intensive irrigated wheat production systems of South Africa through analyses of yield gaps, soil fertility constraints and conservation agriculture practices. The study was conducted in the major irrigation wheat production areas across four geographical regions: KwaZulu-Natal, eastern Highveld, warmer northern and cooler central. Actual yield (Ya) based on long-term yield data ranged from 5.99±0.15 t/ha to 8.32±0.10 t/ha across different geographical regions. The yield potential (Yp) ranged from 7.57 t/ha to 11.45 t/ha. Yield gaps (Yp–Ya) were in the range of 1.58–3.13 t/ha. Yields could be increased by 26–38% through closing yield gaps. On 88.37% and 13.89% of the fields in the KwaZulu-Natal and warmer northern regions, respectively, there was strong evidence of the pra...
South African Journal of Plant and Soil, 2017
Understanding spatial variability of soil nutrients, including that of micronutrients, is importa... more Understanding spatial variability of soil nutrients, including that of micronutrients, is important for establishing best management practices in smallholder crop production. The objective of this study was to determine the status and spatial variability of potentially available zinc (Zn), copper (Cu), manganese (Mn) and iron (Fe) for selective management at Zanyokwe Irrigation Scheme. Soil samples were collected from the 0-20 cm depth on 50 m × 50 m grids and coordinates of the sampling points were recorded using a global positioning system (GPS). The samples were analysed for Zn, Cu, Mn and Fe after extraction with EDTA. The GPS coordinates and corresponding micronutrient values were interpolated using simple kriging to produce continuous raster surfaces, which were then reclassified, using prescribed limits, to produce soil micronutrient maps. Zinc was deficient and exhibited the highest spatial variability, within short distances. There was limited spatial variability of Cu, Mn and Fe. The study highlighted the need for the creation of management zones for Zn availability. Field studies are recommended to establish the extent to which Zn is limiting yields and nutritional quality of crops grown at the scheme.
Soil Science and Plant Nutrition, 2016
This study evaluated effects of oats (Avena sativa L.) and grazing vetch (Vicia dasycarpa L.), bi... more This study evaluated effects of oats (Avena sativa L.) and grazing vetch (Vicia dasycarpa L.), bicultures, in rotation with summer maize (Zea mays), on soil organic matter fractions and activities of selected enzymes. The trial was initiated in April 2009. The treatments were 100% oat, 100% vetch, 90% oat + 10% vetch, 70% oat + 30% vetch, 50% oat + 50% vetch, and weedy fallow, in a randomized complete block design (RCBD) with three replications. Soil samples were collected in October 2011, from the 0-5 and 5-20 cm depths, and analyzed for total carbon (C), particulate organic matter (POM), water-soluble carbon (WSC), microbial biomass carbon (MBC) and activities of selected enzymes. Total C was higher in bicultures, particularly the 70% oat + 30% vetch, and 100% vetch than in 100% oats and the control. The greatest MBC, WSC, dehydrogenase, aryl-sulphatase and phosphomonoesterase activities were in the 70% oat + 30% vetch biculture, and declined where the proportion of oats or vetch was higher. Increasing proportions of vetch resulted in increases in urease and β-glucosidase activity and decrease in POM. The findings suggested that, in addition to increased maize yields, bicultures of oats and vetch also have synergistic effects on soil carbon pools and enzyme activities, with potential benefits of improved soil physical condition and nutrient cycling compared with the individual crops, under warm temperate conditions.
Low winter rainfall poses a challenge to production of high biomass from cover crops, which is ne... more Low winter rainfall poses a challenge to production of high biomass from cover crops, which is necessary for the success of conservation agriculture systems in the Eastern Cape Province of South Africa. An experiment was conducted to evaluate the adaptability of white oats (Avena sativa), grazing vetch (Vicia dasycarpa), rye grass (Lolium multiflorum), barley (Hordeum vulgare), radish (Raphanus sativa) and triticale (Triticale secale) production under low winter rainfall conditions in the Eastern Cape. The cover crop species were relayed into maturing maize (Zea mays L.) in February, March and April of 2010, exposing them to varying rainfall conditions. They were followed with summer maize. Growth rate and final biomass of cover crop species decreased with delayed planting, except for radish. February planted cover crops had the lowest residues remaining at maize planting, resulting in higher weed dry weights at 3 and 6 weeks after planting (WAP). April planted cover crops improved soil N by a greater margin compared to earlier plantings, which were comparable within their category. Grazing vetch and radish resulted in the greatest soil N improvement. Significantly higher (P<0.05) maize grain yield was recorded in grazing vetch, while all other species had comparable yields. It is, thus feasible to produce cover crops under winter rainfall conditions in the Eastern Cape and grazing vetch and radish can serve this purpose.
Developments in Soil Science, 2002
Publisher Summary In the study discussed in the chapter, Bacillus thuringiensis toxins were found... more Publisher Summary In the study discussed in the chapter, Bacillus thuringiensis toxins were found to adsorb onto pure clay minerals and onto humic acids extracted from soils, and the complexes formed from these interactions were less available for microbial degradation. They retained their pesticidal activity longer than free forms. The aim of this study was to analyze the adsorption of the toxin from Bacillus thuringiensis subsp. tenebrionis (Btt) to surface active soil constituents. Clay-sized fractions were separated from a vertisol, an alfisol, and an oxisol after complete dispersion of the soils by mechanical means and the toxin was purified from a Btt commercial preparation. Adsorption isotherms were established by the difference method in deionized water or in phosphate buffer (pH 6.8). Adsorption of Btt toxin was in the order vertisol > alfisol > oxisol, and it was mostly irreversible, except for the alfisol. Adsorption could be explained by physicochemical conditions and the nature of clay constituents—that is, the dominant clay mineralogy: montmorillonite (vertisol) and kaolinite (alfisol, oxisol). The results show that Bt toxins released into the soil may be retained by soil colloids.
South African Journal of Plant and Soil, 2011
ABSTRACT Little research attention has been given to growing summer cover crops as part of conser... more ABSTRACT Little research attention has been given to growing summer cover crops as part of conservation agriculture systems. Three cover crops (sorghum [Sorghum bicolor], mucuna [Mucuna pruriens] and sunhemp [Crotalaria juncea]) were relay-intercropped into maize [Zea mays] 42 days after planting maize. Biomass yields, N uptake and maize yield were measured. In sole cropping, sorghum had the highest dry weight (11 t ha−1) followed by sunhemp (7.2 t ha−1) and mucuna (6.1 t ha−1). However, cover crop biomass yields dropped significantly (85% for sorghum, 70% for sunhemp and mucuna) when relay-intercropped into maize. Nitrogen uptake followed a similar pattern with mucuna having the highest N-uptake of 70 kg N ha−1 in relay-intercropping as compared to the &gt; 250 kg N ha−1 in the sole cropping system. Maize biomass and grain yields were not affected by relay-intercropping cover crops. The low cover crop biomass yields in relay-intercropping may not be viable for sustainable conservation agriculture.
Soil Biology and Biochemistry, 2003
Clay minerals have been shown to reduce the extent and rate of biodegradation of several compound... more Clay minerals have been shown to reduce the extent and rate of biodegradation of several compounds. Here, we investigated the ability of soil clays to protect proteins from biodegradation: the insecticidal protein from Bacillus thuringiensis subsp. tenebrionis (Btt toxin) and Bovine Serum Albumin (BSA). The two proteins adsorbed in large amounts (up to 0.24 g BSA g 21 clay and 0.74 g Btt toxin g 21 clay) and irreversibly to smectite clay particles from a vertisol. We measured the growth of a soil inoculum in the presence of each of proteins as the sole source of carbon. When clay was present in the medium, microbial growth was directly proportional to the amount of free protein (i.e. nonadsorbed). Hence, the two proteins were unavailable when adsorbed to clay. The clay had little influence on the ability of microorganisms to hydrolyse a soluble substrate. The inhibitory effect of clays on utilisation of BSA and Btt toxin was interpreted as being the result of the adsorption of the proteins to clay, which rendered the proteins unavailable for microbial utilisation.
Soil and Tillage Research, 2012
A study was conducted to determine the effects of oat (Avena sativa) and grazing vetch (Vicia das... more A study was conducted to determine the effects of oat (Avena sativa) and grazing vetch (Vicia dasycapa) winter cover crops and fertilization regimes on soil organic matter (SOM) in an irrigated maize-based (Zea mays L.) conservation agriculture (CA) system following four years of continuous practice. Separate plots of oat and grazing vetch cover crops were grown in winter and then maize was planted in all plots in the following summer season. The four fertilization regimes used were: (i) fertilizer applied to the cover crops and the maize crop (F1), (ii) fertilizer applied to cover crops only (F2), (iii) fertilizer applied to the maize crop only (F3) and (iv) no fertilizer applied (F4). Control plots (weedy fallows) were included and the treatments were laid out in a randomized complete block design with three replications. Soil samples from 0-5, 5-20 and 20-50 cm depths were analyzed for total SOM, particulate organic matter (POM) fractions, hot water soluble C (HWC) and C-associated with water stable macro-and microaggregates (WSAC). While total SOM was more concentrated in the 0-5 cm soil depth across treatments, a lack of maize fertilization (F2 and F4 regimes) significantly (P < 0.05) reduced the stratification ratio. Oat and grazing vetch rotations produced significantly higher (P < 0.05) fine POM, coarse POM and HWC than weedy fallow rotations at 0-5 and 5-20 cm. When fertilized, oat was better able to support SOM sequestration in water stable aggregates at 0-20 cm while grazing vetch was more effective at 20-50 cm. The F3 regime had similar SOM levels as the F2. When no fertilizer was applied (F4-regime), there were significant (P < 0.01) reductions in biomass input and total SOM on the oat-maize and weedy fallowmaize rotations whereas the grazing vetch-maize rotation did not respond, both at 0-5 and 5-20 cm. The findings suggested that in the low fertilizer input CA system, targeting fertilizer to the winter cover crop as opposed to the maize crop could give similar SOM response, with less fertilizer invested and that grazing vetch cover crops may be better suited to low N input CA systems for SOM improvement.
Soil and Tillage Research, 2011
Low soil fertility and weeds reduce maize yields on most smallholder (SH) irrigation schemes in S... more Low soil fertility and weeds reduce maize yields on most smallholder (SH) irrigation schemes in South Africa (SA). While cover cropping can increase maize productivity, benefits from different types of mulch are not well understood, leading to challenges in selecting the most appropriate cover crop species to grow. Field experiments investigating the effects of oat (Avena sativa), grazing vetch (Vicia
Environmental Monitoring and Assessment
This exploratory study evaluated biophysical, cultural and socio-economic factors affecting crop ... more This exploratory study evaluated biophysical, cultural and socio-economic factors affecting crop production and land utilisation in the NkonkobeMunicipality, South Africa. The study soughtto establish what farmers in the area perceive as serious threats to crop production,drivers for land abandonment,and how best current agricultural productioncould be intensified. The farmers’ perspectives were assessed through interviews using semi-structured and open-ended questionnaires. The results of the study revealed declining crop productivity and increase in land abandonment in the Municipality. Thebiophysicaldriversoflandabandonmentwerelowanderraticrainfallandlanddegradationwhile the socio-economic drivers were labour shortages due to old age and youth movement to cities, lack of farming equipment and security concerns. The most abandoned crops were maize, sorghum and wheat. This trend was attributed to the labour intensiveness of cereal production and a shift in dietary preference to pur...
Journal of Agriculture and Rural Development in the Tropics and Subtropics, 2018
The diversity of smallholder farms in space, resource endowment, production and consumption decis... more The diversity of smallholder farms in space, resource endowment, production and consumption decisions are often a hindrance to the design, targeting, implementation and scaling out of agricultural development projects. Understanding farm heterogeneity is crucial in targeting interventions that can potentially contribute to improved crop productivity, food security and livelihood sustainability. The study sought to define and understand farm typology in a resettlement smallholder food-cash crop production area in Zimbabwe. Data was collected from five focus group discussions (FGDs), and 102 household interviews. Principal component analysis (PCA), multiple correspondence analysis (MCA) and cluster analysis were used to analyse quantitative and qualitative data variables and aggregate farms into clusters according to production means, socio-economics and demographics. The three identified farm types were (i) resource-endowed, commercial oriented farms, (ii) medium resourced and (iii) ...
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Papers by Pardon Muchaonyerwa