Maize - Pigeon pea Intercrop Resource Use Under Semi-Arid Conditions of Kenya.
A field experiment was conducted at Jomo Kenyatta University of Agriculture and Technology between October 2001 and June 2002 to determine light, water and nitrogen use in maize-pigeonpea intercrop system. The experiment was laid out as a randomized complete block design (RCBD) replicated four times. Treatments included two pigeon pea maturity types; two long duration (erect - ICEAP 00053 and semi-erect - ICEAP 00040) and one medium duration (ICEAP 00557) type intercropped with maize (Katumani) or sole crop. Data on canopy light interception, soil water content changes, crop dry matter accumulation, plant total nitrogen and soil mineral N at key phenological stages were determined. Identification of a suitable reference crop to estimate the amount of N fixed by pigeonpea using the difference method was done in a greenhouse experiment. The experimental design was complete block design replicated three times. Maize (Hybrid 511 and Katumani), sorghum (MB30 and IS 25545) and cotton (Hart 89 M and Uka 591146), were evaluated as reference crops. Sorghum and cotton varieties were also included in the field experiment as reference crops. Maize and sorghum accumulated more shoot and root dry mass compared to pigeonpea both in the field and greenhouse experiment, hence they were unsuitable to be reference crops. Cotton had similar rooting characteristics and phenological development with pigeonpea. Cotton was a suitable reference crop for the long duration but not the medium duration pigeonpea in the greenhouse and in the field. Long duration cultivars had the highest plant N uptake in the field and contributed high amount of N through litter fall XIV and biological fixation compared to medium duration because of higher biomass production. Soil mineral N increased over time during the growing season, possibly due to N contribution through litter fall. Intercropping maize and pigeonpea showed a better use of light than in sole crop. There was a temporal separation in light use in the intercrop system because maize established faster than pigeonpea, hence utilized light early in the season. Pigeonpea intercepted more light when maize was harvested. Long duration pigeonpeas extracted more water than medium duration pigeonpea at the depth of 70-90 em late in the season and maize extracted at 30 -50 ern, possibly indicating that either the long duration pigeonpea had more roots at that depth or the roots were efficient in the extraction of the available soil water an example of spatial separation in water use. Sole maize grain yield in the two seasons were similar (3578 and 3419 kg/ha in season 1 and 2 respectively). Long duration erect pigeonpea had the highest total dry matter hence high yields than long duration semi-erect and medium duration. The average pigeonpea grain yield at the end of the season was 4560, 3203 and 2687 kg/ha for the long duration erect, long duration semi-erect and medium duration respectively. The land equivalent ratio (LER) was 1;23, 1.29 and 1.33 for the long duration erect, long· duration semi-erect and medium duration pigeonpea respectively. There was an increase total biomass, maize grain yield and total N uptake from plots that were previously intercropped than plots with continuous maize crop, which indicated the residual benefits of incorporating pigeonpea in the maize cropping systems. This benefit may be through litterfall decomposition and/or Nrecycling.