Abstract
In this study, soil chemical properties were determined in a cleared forestland continuously grown to cassava (Manihot esculenta Crantz), pigeon pea (Cajanus cajan), maize (Zea mays) and their combination for seven years and from then was fallowed for ten years. Soil samples were also collected from the adjacent cleared uncultivated but fallowed plots as well as the original forestland and analyzed. The objective was to compare nutrient recovery capacity as related to land use history under natural fallow. The study showed that the solely cassava plots were able to recover more available P, exchangeable Mg, CEC and had the highest pH value during the fallow period. Plots grown to sole pigeon pea were able to recover more organic matter, exchangeable K, exchangeable Na and exchangeable acidity than other plots. The control plot had the highest total N, while, the M + P plots recovered more exchangeable Ca. Compared to the year the forest was cleared, OM, CEC, exchangeable Ca, Mg, and Na were able to recover to about their original values, while, total N, exchangeable K and available P could not. Thus, soil nutrient recovery through natural fallow is related to previous cropping history but a period of ten years may be enough for some of the nutrients to recover their original levels.Key words: cropping system, fallowing, nutrient recovery, ultisol
Highlights
The geometric increases in human populations in tropical Africa (Nigeria inclusive) has given rise to the need for agricultural practices to be shifted from traditional extensive system of shifting cultivation to continuous cropping systems (Aweto, 1981) in the form of year round intercropping or monocropping with less than 3 months rest period
It is important to know that during cropping, there is lowering of soil fertility and susceptibility to erosion; this is characteristic of continuous cropping systems because the soil is exposed for long and unprotected from damaging rainfall of high intensity and long duration
MATERIALS AND METHODS Background of the Study This paper is from an on-going long-term research on the sustainability of selected common cropping systems practiced by most farmers in eastern Nigeria
Summary
The geometric increases in human populations in tropical Africa (Nigeria inclusive) has given rise to the need for agricultural practices to be shifted from traditional extensive system of shifting cultivation to continuous cropping systems (Aweto, 1981) in the form of year round intercropping or monocropping with less than 3 months rest period (no fallowing).The soils of Nsukka area in Eastern Nigeria are generally derived from the residua of false-bedded sand-stone or uppercoal measure formations and these geological formations gave the soils their sandy and clayey characteristics respectively with only low to medium inherent nutrient levels (Akamigbo and Asadu, 1983; Asadu, 1990). Farmers use bush fallow, plant residues, household refuse, animal manures and other organic nutrient sources to maintain soil fertility and soil organic matter. This reliance on biological nutrient sources for soil fertility regeneration is adequate with low cropping intensity, it becomes unsustainable with more intensive cropping unless mineral fertilizers are applied (Mulongey and Merck, 1993). It is important to know that during cropping, there is lowering of soil fertility and susceptibility to erosion; this is characteristic of continuous cropping systems because the soil is exposed for long and unprotected from damaging rainfall of high intensity and long duration.
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