Soil and water management is an essential element in food security, agriculture sector growth and sustainable land management of sub-Saharan Africa (SSA). The increased land degradation and declining fertility of SSA soils contribute to food insecurity and poverty. Previously, agroforestry researchers tended to focus mostly on soil nutrient replenishment as being solely responsible for post-fallow crop yield dynamics. Missing from many studies on soil fertility issues is the recognition of the important role of soil physical properties in agricultural productivity. However, many factors affect soil fertility and some agroforestry measures taken to correct soil nutrient deficiencies can also produce desirable soil physical effects. We hypothesized that planted tree fallows can potentially increase soil N status and improve soil physical properties, thus increasing subsequent crop yields. Field studies were conducted on infertile sandy clay loams at Msekera and Kagoro, Zambia, to determine the effect of contrasting fallows (natural fallow, planted non-coppicing and coppicing tree fallows) and no-tree no-fallow [maize (Zea mays L.) with and without fertilizer] on soil fertility and maize yields. This study attempted to address agricultural productivity by viewing soil fertility in terms of both chemical and physical properties. Hence, this report discusses the implications of improving the nutrient status of soils without correcting soil physical constraints. Data from both tree-(agroforestry) and non-tree-based systems have been used to illustrate important physical and chemical changes that occur in soils as a consequence of varying management regimes or cropping systems. Such data show that the concept of soil productivity refers to more than replacement of the lost nutrients. Other aspects include soil structure, soil water retention, water storage, infiltration and soil penetration resistance. The results imply that standard inputs such as mineral or organic fertilizers can maintain only some elements of soil productivity. Therefore, a broader view that incorporates the role of soil physical properties and water in influencing productivity is appropriate. This research does not attempt to provide a comprehensive treatment of all aspects of soil fertility in agroforestry systems. For example, it does not address the role of soil biota diversity in soil productivity.
Tag: litter (births)
Multipurpose tree prunings as a source of nitrogen to maize under semiarid conditions in Zimbabwe. 1. Nitrogen-recovery rates in relation to pruning quality and method of application
Decomposition- and N-mineralization rates of multipurpose tree prunings applied as a source of N to annual crops in agroforestry systems are affected by the chemical composition and method and time of application of the prunings and the soil type. In a greenhouse study undertaken on two contrasting Zimbabwean soils, there was a significant interaction of pruning quality with time and method of pruning application on nitrogen recovery by maize and residual effects on a subsequent maize crop on both soil types. Incorporating prunings in the soil at planting gave higher nitrogen recovery compared to surface application at two or four weeks after planting for all three MPT species used.Flemingia macrophylla showed prolonged N immobilization on an Alfisol (sandy clay loam) but not on the Psamment (sandy soil). Nitrogen recovery by the second maize crop (residual effect) was influenced by pruning quality, time of application, and soil type. Low-quality prunings such asFlemingia macrophylla andAcacia angustissima applied four weeks after planting gave higher residual effect on N recovery on the Alfisol than on the Psamment (3% vs. 6%).