Abstract
A long-term cotton exhaustion trial was conducted on lowland Vertisols and Fluvisols at Werer Agricultural Research Center during the 1968–2002 in Ethiopia to investigate nutrient depletion rate and changes in selected soil chemical properties. Treatments used include cultivated fallow, control, 80kgN ha<sub>-1</sub>, 80-80 kgNP ha<sub>-1</sub>, 80-80kgNKha<sub>-1</sub> and 80-80-80kgNPKha<sub>-1</sub> arranged in RCBD with four and six replications in Vertisols and Fluvisols, respectively. The cotton was grown as a test crop and the status of soil N, P, K, OC, pHe and ECe were periodically monitored every seasons. Seed cotton yield had shown significant response to treatments imposed after 10 and 3 years of continuous cotton mono-cropping, respectively, on Vertisols and Fluvisols, and consistently continued for further 3 consecutive periodical checking years. Then onwards, until the end of the experiment, seed cotton yield didn't showed consistent yield response. Combined analysis revealed highly significant (p < 0.01) yield response to N applications. Despite the long-term continuous mining of soil nutrients through seed cotton harvest and crop residue removal, soil analytical result revealed no indication of depletion in total nitrogen, available K and P. Soil pHe (in both soil types) and ECe only in Fluvisols tend show gradual increase.
Highlights
As a monocrop, cotton production, in the middle and lower Awash River basin, has been started late 1960's and continually been expanded by clearing more land this was previously under natural forest and grass ecology
Mean seed cotton yield values for the entire experimental durations of the long-term exhaustion trials are presented in Table 1 and 2 for Vertisols and Fluvisols, respectively
Even though total nitrogen depletion was not detected from soil test results, observed seed cotton yield response to sole application of N fertilizer with the advance in continuous cotton cropping could be an indication of gradual depletion in available form of soil nitrogen
Summary
Cotton production, in the middle and lower Awash River basin, has been started late 1960's and continually been expanded by clearing more land this was previously under natural forest and grass ecology. The introduction of cultivation to virgin lands leads to change, often deleterious, affecting its ecological balance (Setter et al, 2004; Farifteh et al, 2006; Elgharably et al, 2010). Under irrigated agriculture, this is much pronounced by negatively affecting the chemical, physical and biological properties of the soil (Rasool et al, 2007). The extent and rate of change, depends on inherent edaphic nature of the soil (parent fertility chemical behaviors, etc.), climatic condition and the level of management being practiced (Michael, 2012). It paves a way to look for a possible means that can help to predict the future trends so that corrective measures could be instituted in good time before some deleterious factors affect its potential productivity (Blaga et al, 1993; Muhammad, 2012)
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