Cornelius Chiduza

Bicultures of oat (Avena sativa L.) and grazing vetch (Vicia dasycarpa L.) cover crops increase contents of carbon pools and activities of selected enzymes in a loam soil under warm temperate conditions

ABSTRACT 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.

Effects of oats and grazing vetch cover crops and fertilisation on microbial biomass and activity after five years of rotation with maize

Degraded soil quality could be improved by cover crops. This study determined effects of maize–oats and maize– vetch rotations with or without fertilisation on soil microbial biomass and activity. Winter treatments were oats, vetch and weedy fallow, in rotation with summer maize. Fertilisation strategies were: fertilised cover crop and maize (F1), fertilised cover crops only (F2), fertilised maize only (F3) and no fertiliser (F4). The 2×4 factorial (plus control) was laid out in a randomised complete block design with three replications. After five years, soils were sampled from the 0–5 and 5–20 cm depths and analysed for microbial biomass carbon (MBC), dehydrogenase, β-glucosidase, urease and phosphatase activities. Cover crops resulted in higher MBC and enzyme activities than the weedy fallow. Fertilisation of cover crop (F2) and maize (F3) resulted in similar MBC. The F4 in cover crops and F3 under weedy fallow had similar dehydrogenase activities, whereas F4 under vetch was similar to F3 under oats. The F4 for vetch had similar β-glucosidase activity to F1, and urease activity to F1, F2 and F3, of oats. Phosphatase activities in F1 and F2 were similar. The use of vetch and fertilisation of cover crops stimulated soil biological activity compared with the control.

Decomposition, Nitrogen, and Phosphorus Mineralization from Residues of Summer-Grown Cover Crops and Suitability for a Smallholder Farming System in South Africa

Cover crops, usually grown under conservation agriculture, may offer numerous benefits depending on the farming system. In this study the authors investigated residue decomposition, nitrogen (N) and phosphorus (P) release from mucuna (Mucuna pruriens) and sunhemp (Crotalaria juncea) as well as their uptake by maize in a farming system common in smallholder farms in South Africa. This was done through litterbag, laboratory incubation, and field studies. Sunhemp stems had 65% dry weight remaining after 132 days while just over 10% of mucuna and sunhemp leaves remained. There was no mineral contribution to maize growth by cover crops. However, in incubation studies, mucuna mineralized 60 mg N kg−1 and 3.2 mg P kg−1 and sunhemp mineralized 45 mg N kg−1 and 3.5 mg P kg−1. This suggested that weeds and/or leaching may have impacted negatively to nutrient flow from decaying cover crops species to maize during the long winter fallow period.

Genotype x environment interactions and yield stability of stress-tolerant open-pollinated maize varieties in the Eastern Cape province, South Africa

Genotype × environment interactions are inherent in multilocational trials and complicate identification of superior genotypes. The aim of the study was to determine yield performance and stability of 13 maize genotypes in five locations of the Eastern Cape province, South Africa. The genotypes assessed were: ZM305, ZM423, ZM501, ZM525, ZM621, ZM627 and Obatanpa from the International Maize and Wheat Improvement Centre; BR993 and COMP4 from the International Institute of Tropical Agriculture; four local checks, AFRIC 1, Okavango, Nelsons Choice, and PAN 6479. Yield data were subjected to analysis of variance (ANOVA) and additive main effects and multiplicative interaction (AMMI) analysis. According to ANOVA, genotype × environment interaction was significant. PAN 6479 (5.21 t ha-1) and ZM525 (5.19 t ha-1) were the highest-yielding varieties, whereas Okavango (4.08 t ha-1) showed the lowest yield. Based on AMMI analysis, BR993 and Obatanpa were the least stable genotypes. PAN 6479 and ZM525 showed specific adaptations to high potential environments. Obatanpa was adapted to environments with low-yielding potential, since improvement of the environment did not improve its yield. ZM501 was the most stable genotype, and showed no significant yield difference to PAN 6479. ZM501 can therefore be assigned to several environments in the Eastern Cape.

Tillage and crop rotation effects on carbon sequestration and aggregate stability in two contrasting soils at the Zanyokwe Irrigation Scheme, Eastern Cape province, South Africa

Intensive tillage and monocropping have adversely affected the quality of soils in South Africa through accelerated loss of soil organic matter. Two clay loam soils, a Bonheim at Burnshill and a Shortlands at Lenye, at the Zanyokwe Irrigation Scheme in the Eastern Cape province were used to evaluate the short-term effects of tillage and crop rotations on carbon sequestration and aggregate stability under sprinkler-irrigated crop production. A split-plot arrangement of treatments in a randomised complete block design was used with tillage as the main plots and crop rotations as subplots. Conventional tillage (CT) was compared to no-till (NT) under maize–fallow–maize (MFM), maize– wheat–maize (MWM) and maize–oat–maize (MOM) rotations. Carbon sequestration was monitored by measuring changes in soil organic carbon (SOC) and the stability index (SI) was used for monitoring aggregate stability. No-till had inconsistent effects on SOC relative to CT but resulted in improved soil SI on both soils, especially on the Shortlands soil. The MOM rotation enhanced SOC relative to the MWM and MFM rotations on both the Bonheim and Shortlands soils. Across tillage practices, the MOM rotation significantly increased the soil aggregate SI compared with the MWM and MFM rotations on the Shortlands and to a lesser extent on the Bonheim soils. Scanning electron microscopy revealed that soil aggregates under MOM had dense organic coatings and bridges compared with the MFM rotation, indicating the positive effect of carbon sequestration on aggregate stability. Generally, the results indicated that, in the short term, cover crops, especially oats, have greater influence on SOC accumulation and aggregate stability than tillage, irrespective of soil type.

Conservation agriculture effects on plant nutrients and maize grain yield after four years of maize–winter cover crop rotations

The effects of maize rotation with oat (Avena sativa cv. Sederberg) and grazing vetch (Vicia dasycarpa cv. Max) winter cover crops on nutrient availability, maize grain yield and maize grain nutrient concentration were investigated. Soil samples were collected from the 0–5 and 5–20 cm depths of experimental plots after four years of continuous maize–winter cover crop rotations. Winter cover crops caused small increases of extractable soil Cu, Mn, P and Zn, but not Ca and K, concentrations. A small dose of fertiliser applied to maize (60, 30, 40 and 1.5 kg ha−1 of N, P, K and Zn, respectively) also caused a significant increase in P and Zn, as well as mineral N, concentrations but only in the vetch–maize rotations. Stratification of Mn, K and Zn in the 0–5 cm soil depth occurred in all treatments. Vetch additionally increased maize grain yield, grain N concentration and soil acidity more than either oat or fallow. Non-fertilisation of maize reduced maize grain yield on oat and fallow–maize rotations more than it did on vetch–maize rotations. A combined application of vetch winter cover crops and small doses of fertiliser could significantly improve sustainability of low input maize-based conservation agriculture systems.

A vetch winter cover crop can improve response to nitrogen fertiliser and profitability of no-till maize : short communication

A high nitrogen (N) fertiliser requirement can be a deterrent to the adoption of conservation agriculture (CA). A field trial was carried out to test whether a high biomass-yielding vetch (Vicia dasycarpa L.) winter cover crop can be used to improve N response and profitability of a subsequent maize (Zea mays L.) crop under no-till and irrigation. There were five N fertilisation treatments (0, 60, 120, 180 and 240 kg ha−1). Maize grain yield after vetch was higher than that after a fallow (no winter cover crop) for most of the cases when the N fertiliser application rate was below 180 kg ha−1. Where no N fertiliser was applied, maize yields after vetch were 4.71 and 7.26 tons ha−1 for the first and second seasons, translating into an N fertiliser replacement value of approximately 90 kg N ha−1. The highest marginal rate of return for vetch over the two maize seasons (399% and 649%) was obtained at a fertiliser rate of 0 kg N ha−1. These data from preliminary CA studies in the Eastern Cape highlight the importance of promoting legume winter cover crops as an entry point to CA, especially for poor maize farmers who cannot afford N fertiliser.

Effects of relay inter-cropping summer cover crops with maize on cover crop biomass and maize yields in a warm-temperate region of South Africa : short communications

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 > 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.

Effect of cultivar, seedling age and leaf clipping on establishment, growth and yield of pearl millet (Pennisetum glaucum) and sorghum (Sorghum bicolor) transplants

This study explored the viability of intensifying pearl millet and sorghum production through use of nurseries and transplanting to address the problem of poor stand establishment. The experiments were carried out over two seasons, the 1999/2000 and 2000/2001 seasons in the south eastern lowveld of Zimbabwe where the mean rainfall is less than 500 mm per annum. Treatments included two pearl millet cultivars (PMV2 and PMV3) and two sorghum cultivars (Mutode and Macia). These crops were transplanted with and without leaf clipping at three seedling ages (30, 40 and 50 days for pearl millet; 29, 39 and 49 days for sorghum). Transplants were raised in nursery seedbeds. In the 1999/2000 season, there were significant effects of cultivar (P<0.05) and leaf clipping (P<0.01) on pearl millet grain yield. Clipped seedlings yielded 932 kg ha−1 compared to 797 kg ha−1 for non-clipped seedlings while PMV3 yielded 902 kg ha−1 compared to 820 kg ha−1 for non-clipped seedlings. Mutode yielded significantly (P<0.05) higher than Macia in both seasons, however, leaf clipping tended to increase yields for both cultivars. An increase in seedling age from 29 days also tended to reduce yields. It was concluded that leaf clipping of 30-day old seedlings at transplanting may enhance sorghum and pearl millet yields in the semi-arid tropics.

Sensitivity of selected chemical and biological soil quality parameters to tillage and rotational cover cropping at the Zanyokwe Irrigation Scheme, South Africa

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–oat–maize. 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–oat– maize rotations were clustered together, indicating the similarity of their positive impact on soil quality.