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Browsing by Author "Giller, Ken"

Now showing 1 - 9 of 9
  • Comparative performance of conservation agriculture and current smallholder farming practices in semi-arid Zimbabwe
    Baudron, Frederic; Tittonell, Pablo; Corbeels, Marc; Letourmy, P.; Giller, Ken (Elsevier B.V., 2012)
    Conservation agriculture is promoted in sub-Saharan Africa as a means to improve water use efficiency in an region with variable or poorly distributed rainfall. However, other environmental and social factors may contribute to the success or failure of implementation and practice. The purpose of this study was to compare on-farm conservation agriculture trials of cotton and sorghum with production practices currently in place. Two experiments at multiple locations were executed. The first involved an unfertilized cotton-sorghum rotation (three consecutive seasons), while the second examined cotton production with fertilizer provided on credit (two consecutive seasons). Mulches were produced on site to further emulate conditions present for farmers of the Mid-Zambezi valley. Farmers' perceptions of the technologies involved were also studied. CA was found to have no effect on cotton yields during the first two seasons, which received average or above average rainfall, but was found to be detrimental to yields during a third season of decreased rainfall. Additionally, greater run-off was found in on-farm CA trials in coarser soils than fine-textured soils. Farmers perceived that plowing was necessary to avoid soil crusting and compaction in drier years while CA was beneficial during wetter seasons. The authors site poor mulch coverage as a factor in this result and recommend legume intercropping as part of the solution.
  • Conservation agriculture and smallholder farming in Africa: The heretics' view
    Giller, Ken; Witter, Ernst; Corbeels, Marc; Tittonell, Pablo (Amsterdam, Netherlands: Elsevier B.V., 2009)
    This paper critically analyzes the claims of successful conservation agriculture adoption (CA). CA is said to increase yields, to reduce labor requirements, improve soil fertility and reduce erosion. Yet, according to the authors the empirical evidence is not clear and consistent on many of those points. In sub-Saharan Africa the available evidence suggests virtually no uptake of CA. The authors conclude with a need for critical assessment of the ecological and socio-economic conditions for which CA is best suited.
  • Cotton expansion and biodiversity loss in African savannahs, opportunities and challenges for conservation agriculture: A review paper based on two case studies
    Baudron, Frederic; Corbeels, Marc; Monicat, F.; Giller, Ken (Amsterdam, Netherlands: Springer Netherlands, 2009)
    This article reviews the potential for conservation agriculture to develop productive and environment-friendly cropping systems using the experiences of two African landscapes. Conservation agriculture can potentially benefit biodiversity and turn agriculture from a threat into an opportunity for conservation. The authors also raise a number of challenges inhibiting the growth of conservation agriculture by resource-poor farmers.
  • A fourth principle is required to define Conservation Agriculture in sub-Saharan Africa: The appropriate use of fertilizer to enhance crop productivity
    Vanlauwe, Bernard; Giller, Ken; Corbeels, Marc; Gerard, B.; Nolte, C. (2014)
    Conservation agriculture (CA) is often promoted as a key to intensifying agricultural production in sub-Saharan Africa. Despite significant efforts to promote CA, however, adoption remains limited in this region. This article contends that CA requires a fourth principle of appropriate fertilizer use to complement the already accepted principles of minimal tillage, maintaining a soil cover, and crop diversification. In regions where CA was widely adopted, fertilizer application was an essential part of agricultural systems, and a key to the success of CA. Appropriate fertilizer application is necessary for CA to be a successful alternative to conventional production in sub-Saharan Africa.
  • Long-term impact of reduced tillage and residue management on soil carbon stabilization: Implications for conservation agriculture on contrasting soils
    Chivenge, P. P.; Murwira, H. K.; Giller, Ken; Mapfumo, P.; Six, J. (Elsevier, 2007)
    The long-term effects of tillage system and residue management on soil organic carbon stabilization are studied in two tropical soils in Zimbabwe, a red clay and a sandy soil. The four tillage systems evaluated were conventional tillage (CT), mulch ripping (MR), clean ripping (CR) and tied ridging (TR). Soil organic carbon (SOC) content was measured for each size fraction as well as total SOC. Based on the findings, the authors conclude that residue management - maintaining carbon inputs - is most important for SOC stabilization in coarse-textured soils, whereas reducing tillage is the management priority for fine-textured soils.
  • Maize productivity and mineral N dynamics following different soil fertility management practices on a depleted sandy soil in Zimbabwe
    Chikowo, R.; Mapfumo, P.; Nyamugafata, P.; Giller, Ken (Elsevier B.V., 2003)
    There is a need for an improved understanding of nitrogen (N) dynamics in depleted sandy soils in southern Africa. A field experiment was conducted to evaluate the performance of different soil fertility improvement practices on a degraded granitic sandy soil in Zimbabwe. Legumes capable of accumulating large amounts of N through biological N2 fixation and subsoil N capture were tested against soybean/maize rotation, cattle manure fertilization and continuous maize (Zea mays L) with or without fertilizer. Soybean (Glycine max) accumulated 82 kg ha.1 N (seed + stover), while mucuna (Mucuna pruriens) produced 87 kg ha.1 N in its biomass. Soybean fixed 76% of its N, while mucuna fixed 96% of the accumulated N as estimated by the 15N natural abundance method. Although the following maize crop in the second season suffered from drought stress, maize N uptake was 14.8 kg ha.1 following soybean and 16.4 kg ha.1 following mucuna, compared with 5.2 kg ha.1 for the unfertilized maize and 25.6 kg ha.1 for the maize fertilized with N at 90 kg ha.1. Cajanus cajan and Crotalaria paulina added barely 10 kg ha.1 of N through their biomass and had no effect on N uptake by maize. Apparent recovery of the added N by maize was 47% for the fertilized maize, 36% for soybean, 12% for mucuna and 9% for cattle manure. There was very little partitioning of N into grain and uptake was mostly before the onset of the drought. Despite the large differences in added residue N, differences in soil mineral N were only evident up to 4 weeks after the beginning of the rains, after which mineral N concentrations became very small in all treatments due to leaching, rather than crop uptake. By the eighth week after crop emergence, maize root length density had increased to about 0.1 cm cm.3 at the 60-80 cm depth, the rapid increase apparently stimulated by the drought. It was concluded that mineral N available to maize from the residues tested falls short of what is required to sustain high maize yields. In these environments where biomass accumulation in many legumes is restricted by soil biophysical factors (poor nutrient concentrations, acidity, coarse texture), combinations of legume rotations and mineral N fertilization will remain the most viable option for sustainable agriculture. © 2003 Elsevier B.V. All rights reserved.
  • A meta-analysis of long-term effects of conservation agriculture on maize grain yield under rain-fed conditions
    Rusinamhodzi, L.; Corbeels, Marc; van Wijk, M. T.; Rufino, M. C.; Nyamangara, J.; Giller, Ken (Springer, 2011)
    Conservation agriculture is often encouraged for use in rain-fed maize systems in Southern Africa. The purpose of this meta-analysis is to identify the factors on maize yield in these conditions. Twenty-six studies lasting over 5 years were analyzed. Results indicate much variability and dependence on multiple influences on yield, such as rainfall, mulch cover, soil texture, nitrogen inputs, and climate. Some results include: mulch cover in high rainfall areas leads to lower yields, well-drained soils are necessary in order to see improved yields over time, and higher nitrogen inputs are necessary to achieve higher yields. The authors conclude that conservation agriculture and its related techniques must be adapted to specific biophysical conditions in order to have a beneficial impact on maize yields.
  • Socio-ecological niches for minimum tillage and crop residue retention in continuous maize cropping systems in smallholder farms of central Kenya
    Guto, S. N.; Pypers, P.; Vanlauwe, Bernard; de Ridder, N.; Giller, Ken (Madison, WI: American Society of Agronomy, 2011)
    The prevalence of soil degradation and production constraints for smallholder farmers in Central Kenya offers an opportunity for the application of conservation agriculture practices. However, much variability exists between smallholders, rendering the benefits of CA quite site specific. The purpose of this study was to determine the effects of minimum tillage and mulches on maize yields of twenty-one farms with varying soil fertility, size, and, cropping seasons. Two tillage and two crop residue trials were compared across three soil fertility classes from 2007 to 2009. It was determined that minimum tillage practices are inappropriate for good and poor soil fertility and most beneficial for farms of medium soil fertility. In order to raise agricultural productivity in Sub-Saharan Africa, additional studies that account for heterogeneity among smallholders is critical.
  • Tillage and vegetative barrier effects on soil conservation and short-term economic benefits in the Central Kenya highlands
    Guto, S. N.; Pypers, P.; Vanlauwe, Bernard; de Ridder, N.; Giller, Ken (Elsevier, 2011)
    Integrating vegetative soil erosion barriers with minimum tillage practices can be an economically viable method in reducing soil loss in intensively managed sloping land in the East African Highlands. This study sought to compare minimum and regular tillage practices with and without vegetative barriers (leucaena and Napier) under local farming conditions in Kenya. Minimum tillage yields of soybean and maize were superior to conventional, except in instances of root competition within the Napier no-till trial. Minimum tillage trials without barriers experienced significant soil loss during periods of heavy rainfall and had the lowest marginal rate of returns. Napier barriers with conventional tillage conserved the most soil and represented an economically viable option; however, leucaena barrier use couple with conventional tillage was found to be a less risky practice with even greater economic returns. Longer term studies in multiple locations are necessary to determine impacts across a highly varied cohort of smallholder farmers in the African Highlands.