The widespread planting of Sesbania sesban fallows for replenishing soil fertility in eastern Zambia has the potential of causing pest outbreaks in the future. The pure S. sesban fallows may not produce enough biomass needed for replenishing soil fertility in degraded soils. Therefore, an experiment was conducted at Kagoro in Katete district in the Eastern Province of Zambia from 1997 to 2002 to test whether multi-species fallows, combining non-coppicing with coppicing tree species, are better than mono-species fallows of either species for soil improvement and increasing subsequent maize yields. Mono-species fallows of S. sesban (non-coppicing), Gliricidia sepium, Leucaena leucocephala and Acacia angustissima (all three coppicing), and mixed fallows of G. sepium + S. sesban, L. leucocephala + S. sesban, A. angustissima + S. sesban and natural fallow were compared over a three-year period. Two maize (Zea mays) crops were grown subsequent to the fallows. The results established that S. sesban is poorly adapted and G. sepiumis superior to other species for degraded soils. At the end of three years, sole G. sepium fallow produced the greatest total biomass of 22.1 Mg ha1 and added 27 kg ha1 more N to soil than G. sepium + S. sesban mixture. During the first post-fallow year, the mixed fallow at 3.8 Mg ha1 produced 77% more coppice biomass than sole G. sepium, whereas in the second year both sole G. sepium and the mixture produced similar amounts of biomass (1.6 to 1.8 Mg ha1). The G. sepium + S. sesban mixture increased water infiltration rate more than sole G. sepium, but both these systems had similar effects in reducing soil resistance to penetration compared with continuous maize without fertilizer. Although sole G. sepium produced high biomass, it was G. sepium + S. sesban mixed fallow which resulted in 33% greater maize yield in the first post-fallow maize. However, both these G. sepium-based fallows had similar effects on the second post-fallow maize. Thus the results are not conclusive on the beneficial effects of G. sepium + S. sesban mixture over sole G. sepium
Tag: infiltration
The effectiveness of contour hedgerows for soil and water conservation
Woody species alongside earth contour bunds enhance the soil water-infiltration capacity in the Sahel, West Africa
Land degradation, including the loss of tree, forest and vegetation cover, and its related loss of water availability are the main constraints affecting the rainfed agricultural systems in West African Sahel and dry savanna. Therefore, farmers are implementing various soil and water conservation techniques such as zaï pits, half-moons, contour stone and earth bunds to improve crop production through reduced erosion and enhanced water retention. This study explores the effect of woody and herbaceous vegetation established along earth contour bunds on soil infiltration capacity in southern Mali. The soil infiltration measurements were carried out from September to December 2019 using single ring infiltrometers up-slope and down-slope of the bunds built on contour lines in 2015 and 2016 with four types of vegetation: (1) natural annual herbaceous vegetation; (2) planted Andropogon gayanus (perennial grass); (3) planted Gliricidia sepium (woody species) and (4) planted Acacia colei (woody species). The field-saturated hydraulic conductivity (Kfs) was estimated from the infiltration data and subjected to statistical analysis to compare the effect of the four types of vegetation on soil infiltration capacity. The results revealed significant differences in infiltration rate and Kfs between the four vegetation types. The highest infiltration rate and Kfs were observed for earth contour bunds reinforced with woody species G. sepium (299.5 ± 0.6; 45.3 ± 1.4 mm h−1), followed by A. colei (232.2 ± 2; 38.2 ± 1.6 mm h−1). These were followed by the grass A. gayanus (189.4 ± 2.5; 33.0 ± 1.7 mm h−1) and natural annual herbaceous vegetation (132 ± 2.3; 20.7 ± 1.9 mm h−1). In addition, soil water-infiltration rate and Kfs were higher for down-slope compared to up-slope areas for the two woody species. In practice, it is appropriate for farmers to reinforce contour bunds with woody species and perennial herbs given the beneficial effect on soil water infiltration and retention capacity and the expected socio-economic benefit they can get from them.