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LEGUMES

Do Mixed-Species Legume Fallows Provide Long-Term Maize Yield Benefit Compared with Monoculture Legume Fallows?

^a Kenya Forestry Research Institute (KEFRI), P.O. Box 20412-00200, Nairobi, Kenya
^b MacArthur Agro-Ecology Research Centre, 300 Buck Island Ranch Rd., Lake Placid, FL 33852
^c Institute of Crop Science and Resource Conservation (INRES), Dep. of Plant Nutrition, Univ. of Bonn, Karlrobert-Kreiten-Strasse 13 53115, Bonn, Germany
^d Plant Production Systems, Dep. of Plant Science, Wageningen Univ., P.O. Box 430, 6700 AK, Wageningen, the Netherlands
^e Inst. of Plant Production and Agroecology, Univ. of Hohenheim, 70593 Stuttgart, Germany. The reported research was conducted both at KEFRI and at Imperial College, University of London, UK

^* Corresponding author (jndufa{at}africaonline.co.ke).

The deliberate planting of fast-growing N₂–fixing legume monoculture species in rotation with cereal crops can be an important source of N for soil fertility replenishment. We hypothesized that mixed-species fallows have a higher potential of giving long-term residual benefits in terms of biomass, nutrients, and quality of residuals leading to long-term nutrient supply to postfallow maize (Zea mays L.) crops. To test these hypotheses, two experiments were established in farmers' fields on very fine Kandiudalfic Eutrudox soils with monoculture and mixed-species fallows. Treatments included: sesbania [Sesbania sesban (L.) Merr.], crotalaria (Crotalaria grahamiana Wight and Arn.), pigeonpea [Cajanus cajan (L.) Millsp.], siratro [Macroptilium atropurpureum (DC.) Urb.], and calliandra (Calliandra calothyrsus Meissn.) as monoculture-species fallow and mixture fallows of sesbania + crotalaria, sesbania + pigeonpea, sesbania + siratro, or sesbania + calliandra compared with continuous maize cropping with or without N fertilizer, and natural weed fallow. Total aboveground biomass ranged from 4.1 to 20.5 Mg ha^–1 for monoculture and 7.8 to 23.3 Mg ha^–1 for mixed-species fallows. Recyclable fallow biomass N ranged from 70 to 313 kg ha^–1 and there was a positive interaction in some mixtures leading to increased N accumulation. Postfallow maize yields for fallows over five cropping seasons were 161–272% or 61–103% higher when compared with continuous maize without or with N fertilizer, respectively. Long-term postfallow effects on maize yield were linearly related to the amount of recycled fallow N yield. Thus, choice of fallow species to mix should be primarily driven by a better risk management strategy and an increased basket of multiple products and services.

Abbreviations: ADF, acid detergent fiber • LR, long rainy season • SR, short rainy season

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Received for publication November 25, 2008.