A meta-analysis of long-term effects of conservation agriculture on maize grain yield under rain-fed conditions

Conservation agriculture involves reduced tillage, permanent soil cover and crop rotations to enhance soil fertility and to supply food from a dwindling land resource. Recently, conservation agriculture has been promoted in Southern Africa, mainly for maize-based farming systems. However, maize yields under rain-fed conditions are often variable. There is therefore a need to identify factors that influence crop yield under conservation agriculture and rain-fed conditions. Here, we studied maize grain yield data from experiments lasting 5 years and more under rain-fed conditions. We assessed the effect of long-term tillage and residue retention on maize grain yield under contrasting soil textures, nitrogen input and climate. Yield variability was measured by stability analysis. Our results show an increase in maize yield over time with conservation agriculture practices that include rotation and high input use in low rainfall areas. But we observed no difference in system stability under those conditions. We observed a strong relationship between maize grain yield and annual rainfall. Our meta-analysis gave the following findings: (1) 92% of the data show that mulch cover in high rainfall areas leads to lower yields due to waterlogging; (2) 85% of data show that soil texture is important in the temporal development of conservation agriculture effects, improved yields are likely on well-drained soils; (3) 73% of the data show that conservation agriculture practices require high inputs especially N for improved yield; (4) 63% of data show that increased yields are obtained with rotation but calculations often do not include the variations in rainfall within and between seasons; (5) 56% of the data show that reduced tillage with no mulch cover leads to lower yields in semi-arid areas; and (6) when adequate fertiliser is available, rainfall is the most important determinant of yield in southern Africa. It is clear from our results that conservation agriculture needs to be targeted and adapted to specific biophysical conditions for improved impact

Biophysical interactions in tropical agroforestry systems

sequential systems, simultaneous systems Abstract. The rate and extent to which biophysical resources are captured and utilized by the components of an agroforestry system are determined by the nature and intensity of interac-tions between the components. The net effect of these interactions is often determined by the influence of the tree component on the other component(s) and/or on the overall system, and is expressed in terms of such quantifiable responses as soil fertility changes, microclimate modification, resource (water, nutrients, and light) availability and utilization, pest and disease incidence, and allelopathy. The paper reviews such manifestations of biophysical interactions in major simultaneous (e.g., hedgerow intercropping and trees on croplands) and sequential (e.g., planted tree fallows) agroforestry systems. In hedgerow intercropping (HI), the hedge/crop interactions are dominated by soil fertility improvement and competition for growth resources. Higher crop yields in HI than in sole cropping are noted mostly in inherently fertile soils in humid and subhumid tropics, and are caused by large fertility improvement relative to the effects of competition. But, yield increases are rare in semiarid tropics and infertile acid soils because fertility improvement does not offse

Description du système racinaire de trois espèces fourragères en zone soudano-sahélienne : Andropogon gayanus, Vigna unguiculata et Stylosanthes hamata

Description of root systems of three fodder crops in the Soudano-Sahelian area: Andropogon gayanus, Vigna unguiculata and Stylosanthes hamata. Root systems of fodder crops (Andropogon gayanus, Vigna unguiculata and Stylosanthes hamata) were studied at two Research Stations in Mali in 1992, using soil monoliths. In this method, roots are studied throughout the soil profile in cubical compartments of 1 dm3. Root biomass production of A. gayanus planted in 1951 was 4 t.ha-1 against 5 t.ha-1 when planted in 1991. Above-ground biomass was 12 and 8 t.ha-1, respectively. The majority (90%) of the root biomass was concentrated in the upper 60 cm of the soil profile even if the root depth reached 180 cm. Root biomass decreased with depth following a negative exponential curve, but root length density decreased to a lesser extent, resulting in increasing specific root length (root length per unit of root biomass) with depth. Root biomass of V. unguiculata was 1,118 kg.ha-1 without phosphorus fertilization and 2,922 kg.ha-1 with Pfertilization. The effect of Pon above ground biomass was negligible, and no reduction of specific root length with depth was observed. Root biomass production by S. hamata hardly responded to P fertilization: 3,596 kg.ha-1 without P and 4,161 kg.ha-1 with non-limiting P-supply; above-ground biomass was 8,360 and 10,680 kg.ha-1 respectively. Root length density was relatively high for the whole root profile and specific root length increased from 35 m.g-1 for the 0–20 cm layer to 100 m.g-1 for the 130–140 cm layer, allowing S. hamata to use water and nutrients efficiently throughout the whole profile