Barbara Maasdorp

The effect of managing improved fallows of Mucuna pruriens on maize production and soil carbon and nitrogen dynamics in sub-humid Zimbabwe

Mucuna pruriens has emerged as a successful forage or green manure legume for use in the smallholder animal-livestock systems of Zimbabwe. The efficiency of N recovery from mucuna residues in subsequent maize crops can be low and the loss of nitrate nitrogen from the soil profile prior to maize N demand is proposed as a reason for this. An experiment was established in the 1999–2000 wet season at seven on-farm sites in a communal farming district of Zimbabwe (average rainfall 650–900 mm) on acidic (pH < 5), and inherently infertile soils with texture ranging from sandy/sandy loam (n = 5) to clay (n = 2). Improved fallows of mucuna grown for 19 weeks produced between 4.7 and 8.5 t/ha dry matter (DM) at the sandy/sandy loam sites and between 9.5 and 11.2 t/ha DM at the clay sites. This biomass was then either cut and removed as hay, or ploughed in as a green manure. Weedy fallow treatments, which represent typical farmer practice, produced 3.3–6.3 t/ha DM. A maize crop was then grown on these same sites in the following 2000–2001 wet season and the dynamics of soil N and C and maize production were investigated. Where mucuna was green manured, a positive linear response (r2 = 0.72) in maize yield to increasing mucuna biomass (containing 101–348 kg N/ha) was found. On the sandy sites, and where no P fertiliser was applied to the previous mucuna phase, a maize grain yield of 2.3 t/ha was achieved following the mucuna green-manure system; this was 64% higher than the maize yield following the weedy fallow and 100% higher than the maize yield following the mucuna ‘removed’ hay system. Apparent nitrogen recoveries in the range of 25 to 53% indicate that there are large quantities of nitrogen not utilised by the subsequent maize phase. The loss of 73 kg/ha of nitrate N from the soil profile (0–120 cm) early in the wet season and prior to maize N demand is proposed as a reason for low N recovery. No change in labile C (measured with 333 mM KMnO4) was detected through the soil profile at this time and it is suggested that labile C movement occurred between the sampling times.

Contribution of associative N2-fixation (Acetylene reduction) in some grassland ecosystems in zimbabwe

Abstract Many grass species were screened by the C 2 H 2 reduction assay for associated N 2 -fixation. Most showed positive activity, yet none proved particularly superior to the others. Concentrated study on a few species revealed that N 2 -fixation was greatly depressed as soil moisture decreased to even moderate levels. It was concluded that in Zimbabwe, appreciable grass-associated N 2 -fixation is likely to be restricted to vlei areas (low-lying, seasonally waterlogged areas). N 2 -fixation associated with Paspalum urvillei , a vlei species, was estimated to contribute up to 76 kg N ha −1 yr −1 and had nitrogenase activity of 39–48% of the pasture legume Silverleaf Desmodium.

Selection of optimum vegetative indices for the assessment of tobacco float seedlings response to fertilizer management

The experiment sought to establish the vegetative indices for assessing tobacco float seedling varieties’ response to different fertilizer rates. A factorial design, with 3 variety × 4 fertilizer management treatments, was used. The N : P : K treatments were applied at 7, 21, and 35 days after sowing, while N treatments were applied at 42 days. Radiometric measurements were taken at 49, 56, 64, and 79 days after sowing on 8 tray plots, using a multispectral radiometer. Mature seedling samples were harvested at day 79 and stem lengths were determined before processing for total N analysis. All the five channels of the radiometer, the NDVI, and the SRI had a strong relationship with fertiliser rate. Both the NDVI and SRI for T66 were greater (𝑃<0.05) than those for KRK26 and KE1. The SRI had a stronger relationship with seedling dry mass, seedling count/tray, and stem length than the NDVI. The NDVI also showed a stronger relationship with total N than the SRI. The minimum threshold SRI and NDVI values and optimum growth (100% fertilser) were 0.72 and 6.1. This information is useful in identifying and estimating tobacco seedbed area and seedling vigour using remote sensing and, therefore, is important in forecasting potential tobacco crop area and yield.

On-farm productivity of Acacia angustissima, Calliandra calothyrsus and Leucaena leucocephala in a subhumid area in Zimbabwe

Smallholder dairy farmers in Natural Region II, especially in Chikwaka Communal Area, adopted Acacia angustissima, Calliandra calothyrsus and Leucaena leucocephala in the 1995/96 season as alternatives for supplementing expensive commercial dairy feeds. Although several on-station trials have been done in the subhumid region of Zimbabwe, there have been no studies assessing on-farm yields of the introduced fodder species. This study evaluated productivity in a communal area under varying soil (pH, nitrogen, phosphorus and potassium) and management conditions (protection and tree density). Leaf productivity was high on farms with relatively higher soil P. Leaf yields ranged from 0.4–3.3 t DM ha−1 for A. angustissima, 0.8–5.6 t DM ha−1 for C. calothyrsus and 0.2-0.7 t DM ha−1 for L. leucocephala, with mean values of 2.2, 2.6 and 0.4 t DM ha−1, respectively. The low yields of L. leucocephala were associated with psyllid (Heteropsylla cubana) infestation. Decrease in tree density (low population) resulted in reduced yield. Poor performance was also attributed to uncontrolled browsing. Influence of soil characteristics could not be confirmed, but there were indications that low soil phosphorus may have adversely affected tree growth. The yields were generally lower than on-station, which implies that there is room for improving fodder tree yields in this subhumid region, through improving the availability of P, planting a high density of trees, and protecting them from uncontrolled browsing.

Southern African pasture and forage science entering the 21st century : past to present

Given the global challenges of mitigating and alleviating land degradation and ensuring food security, particularly through protein production, pasture and forage science together with rangeland science will remain imperative to sustainable livestock production systems. Recognising the scientific principles developed in this discipline the past 50 years and more in Southern Africa, customary to our diverse and unique environmental conditions will continue to guide and identify future research priorities. A journey from the past to the present can assist in avoiding reinvention and repetition of pasture research. This review highlights how research priorities have either remained the same over time or where research has received less or more priority. The review further illustrates that there has been more interest in species adaptation to drought, pasture and forage water relations, alternative pasture and forage species, and the combination of pasture species in the 21st century than in the 20th century. In conclusion, the soil–plant– livestock complex can serve as a conceptual basis for more effective research together with pasture breeding and nutrition. Finally, researching pasture and forage sciences in an inter- and multi-disciplinary manner clearly supports the principles of holism applied by General JC Smuts, one of the first pioneers of pasture and forage sciences.

Remote Sensing Applications in Tobacco Yield Estimation and the Recommended Research in Zimbabwe

Tobacco crop area and yield forecasts are important in stabilizing tobacco prices at the auction floors. Tobacco yield estimation in Zimbabwe is currently based on statistical surveys and ground-based field reports. These methods are costly, time consuming, and are prone to large errors. Remote sensing can provide timely information on crop spectral characteristics which can be used to estimate crop yields. Remote sensing application on agriculture in Zimbabwe is still very limited. Research should focus on identifying suitable reflectance indices that are related to tobacco growth and yield. Varietal yield response to fertiliser and planting dates as well as suitable temporal windows for spectral data collection should be identified. The challenges of the different tobacco land sizes have to be overcome by identifying suitable satellite platform, with sufficient spectral resolution to separate the tobacco crop from the adjacent competing crops and noncrop vegetative surfaces. The identified suitable index should be strongly correlated with tobacco in season dry mass and yield. The suitable vegetative indices can be employed in establishing tobacco cropped area and then apply the long-term area yield relationship from government and nongovernmental statistical departments to estimate yield from remote sensing derived cropped area.

The potential of replacing conventional dairy supplements with forage legume-based diets in Zimbabwe’s smallholder dairy sector

The effect of replacing commercial supplements with isoenergetic and isonitrogenous velvet bean-, cowpeaand lablab-based supplements on milk yield, milk quality and economic returns in smallholder crossbred dairy cows was investigated in the 2013 and 2014 dry seasons. Using 3 × 3 Latin square designs, nine multiparous Red Dane, Guernsey and Holstein-Friesian crosses in mid-lactation (130 ± 19 d) were offered forage legume-based supplements for 63 d at 0.5 kg per litre of milk produced. Milk quantity and quality were significantly (P < 0.05) different among supplements in both seasons. Cows fed commercial supplements had higher milk yield than cows fed forage legume supplements. Milk fat content was significantly (p < 0.05) higher in cows fed lablab-based supplements than cows fed other supplements. Milk protein, total solids and lactose content of cows fed commercial supplements was significantly (p < 0.05) higher than those fed forage legume-based supplements, although protein content was similar to cows fed lablab-based supplements. Dietary gross margins were higher for cows fed velvet beanand lablab-based supplements by 17% and 16.5%, respectively. Based on supplement, production costs per litre of milk was higher by 28% and 23% using commercial supplements compared to velvet bean and lablab supplements, respectively.

Assessing the Spectral Separability of Flue Cured Tobacco Varieties Established on Different Planting Dates and under Varying Fertilizer Management Levels

The NDVI was used to discriminate tobacco variety, assess fertilizer levels, and determine the impact of planting date on separating crops. A split plot design with four planting dates, September, October, November, and December, as main plots, variety as subplot, and fertilizer treatments as sub-subplots was used. Radiometric measurements were taken from 5 m × 5 m sampling plots, using a multispectral radiometer. The September, October, and November crops had significant variety x fertilizer treatment differences () from the age of 10 weeks. T 66 and KRK26 varieties had similar () NDVI values and these were greater () than those for K E1. The 100% and the 150% fertilizer treatments were similar () and both were greater () than the 50% fertilizer treatments. All of the fertilizer and variety treatments at the December planting dates had similar reflectance characteristics (), which were lower () than the September and October planting dates. The results showed that planting dates, varieties, and fertilizer levels could be distinguished using spectral data. Weeks 10-11 and 15 after the start of the experiment were optimal for separating the planting date effect.

Spectral Indices: In-Season Dry Mass and Yield Relationship of Flue-Cured Tobacco under Different Planting Dates and Fertiliser Levels

This experiment investigated the relationship between tobacco canopy spectral characteristics and tobacco biomass. A completely randomized design, with plantings on the 15th of September, October, November, and December, each with 9 variety × fertiliser management treatments, was used. Starting from 6 weeks after planting, reflectance measurements were taken from one row, using a multispectral radiometer. Individual plants from the other 3 rows were also measured, and the above ground whole plants were harvested and dried for reflectance/dry mass regression analysis. The central row was harvested, cured, and weighed. Both the maximum NDVI and mass at untying declined with later planting and so was the mass-NDVI coefficient of determination. The best fitting curves for the yield-NDVI correlations were quadratic. September reflectance values from the October crop reflectance were statistically similar (), while those for the November and the December crops were significantly different () from the former two. Mass at untying and NDVI showed a quadratic relationship in all the three tested varieties. The optimum stage for collecting spectral data for tobacco yield estimation was the 8–12 weeks after planting. The results could be useful in accurate monitoring of crop development patterns for yield forecasting purposes.

Promoting the use of home-mixed supplements as alternatives to commercial supplements in smallholder beef production systems in the subhumid region of Zimbabwe

The economic and performance effect of supplementing smallholder cattle by substituting commercial feed with iso-nitrogenous and iso-energetic diets based on alternative protein sources was investigated in two trials. In trial 1, three diets (commercial concentrate, commercial concentrate partially substituted with mucuna, and commercial concentrate partially substituted with lablab–cowpea) compared with veld grass were allocated to 12 cattle in a complete randomised block design. In trial 2, a double complete randomised block design with 40 cattle assigned to four forage legume-based diets, a poultry-based diet and a commercial beef concentrate was carried out. Diets were offered at 1.5% of body weight daily over 56 d. Average daily weight gain (ADWG) was measured weekly in trial 1 and fortnightly in trial 2. In trial 1, ADWG was significantly (p < 0.05) higher for animals on supplements compared with non-supplemented cattle. In trial 2, ADWG was significantly highest on the groundnut stover-based diet and least on the poultry litter diet. Supplementation had a positive effect on ADWG and economic performance of smallholder beef cattle. Substitution of commercial concentrates with alternative protein sources reduced diet costs and significantly improved gross margins.