What role can planted fallows play in the humid and sub-humid zone of West and Central Africa? |
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Authors: | Stefan Hauser Christian Nolte Robert J Carsky |
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Affiliation: | 1. International Institute of Tropical Agriculture, Humid Forest Ecoregional Centre, Mbalmayo, Yaoundé, Cameroon 3. L.W. Lambourn & Co, Carolyn House, 26 Dingwall Road, CR9 3EE, Croydon, UK 2. Africa Rice Center (WARDA), Bouaké, C?te d’Ivoire
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Abstract: | Crop management without fertilizer input, which is commonly practiced by most farmers in the humid forest zone of West and
Central Africa, requires soil fertility replenishment during a fallow period. Hypothetical relationships between fallow length
and crop yields assume, that after the cropping phase replenishment starts with high annual increments, leading to an early
recovery of most soil fertility, then slowly approaching a maximum level. The few available empirical data, however, indicate
that this assumption is wrong. Within the first 8 years of fallow, biomass and nutrient accumulation is either progressive
(low initial increments) or linear. Planted fallows are supposed to replenish soil fertility faster or to higher levels than
natural regrowth and should thus lead to higher crop yields. Two major types of planted fallow are distinguished: tree-based
and herbaceous fallows. Data from West and Central Africa do not confirm that tree based fallows are generally capable of
attaining higher crop yields than natural regrowth or other planted fallows. The majority of experiments with tree-based fallows
showed no differences to the control (60.0%). Crop yield declines were found in 15.7% of cases, and only 24.3% resulted in
significant yield increases. Changes in soil properties were more frequently positive (34.3%) than negative (9.8%), yet, most
often (55.9%), there was no effect. Herbaceous fallow had dominantly positive effects on crop yields (52.5% of cases), with
only 3% of cases in which significant reductions were observed. Positive features of some herbaceous fallows, such as easy
establishment, rapid weed suppression, and labor efficient slash-and-burn crop establishment make the technology more likely
to be accepted and adopted by farmers. It appears that fallows have to be specifically designed for responsive crops, i.e.
maize. It is unlikely that one type of fallow can serve the multitude of crops and intercrops grown in the region. Depending
on the major constraints to crop production or income generation, planted fallows have to be specifically designed to address
these constraints. This may require de-emphasizing the soil fertility aspect and focusing on marketable fallow by-products,
weed and pest suppression and reduced labor requirements. Thus, future impact through research on planted fallows will depend
on exact targeting of specific fallow types and species to the most responsive crops and to explicit farmer circumstances. |
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Keywords: | Crop yield response Herbaceous Leguminous fallow Soil fertility replenishment Tree-based |
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