Light, water, and nitrogen use in low input maize-pigeonpea intercrop in subhumid Kenya

Abstract

A field experiment was conducted to investigate light, water and nitrogen use in a low input maize-pigeonpea intercrop system in sub-humid conditions at the University of Nairobi, Kabete Field Station. Treatments were three pigeonpea (Cajanus cajan) varieties; a medium duration (ICEAP 00557) and two long duration types, semi-erect (ICEAP 00040) or erect (ICEAP 00053), planted alone or intercropped with maize (Zea mays)(HSll). Two cotton (Gossypium hirsutum) varieties (Hart 89 M and UKA 59/146) were used as reference crops to determine amount of N fixed by pigeonpea using the N difference method. The experiment was laid out in a randomized complete block design (RCBD) replicated six times. Data on canopy light interception, changes in soil water, crop dry matter accumulation, grain yield, plant total nitrogen and soil mineral N at key phenological stages was determined. There were two maize cropping seasons; April-September 2001 and October- April 2002 as seasons 1 and 2 respectively, but one season of pigeonpea crop. Peak photosynthetically active radiation (PAR) interception in intercropped pigeonpea occurred after maize was harvested in both seasons. The long duration .yarieties intercepted more PAR than medium duration variety. The long dura.tion pigeonpea intercrop extracted more soil water than either of the component sole crops. Long duration pigeonpea had a larger canopy and extracted more soil water than the medium duration pigeonpea Sole maize had highest water use efficiency while sole pigeonpea had the least. Maize average grain yield was 4339 kg ha" and that of pigeonpea was 1400 kg ha". Long duration pigeonpea had significantly higher yield (1600 kg ha') than medium duration pigeonpea (935 kg ha"). The land equivalent ratio (LER) was 1.0,0.96, and 0.84 for maize intercropped with the ICEAP 00040, ICEAP 00053 or ICEAP 00557, respectively, indicating lack of pigeonpea - maize-intercropping advantage. There was better N use in the intercrop than in the sole cropped pigeonpea system The long duration pigeonpea :fixed more nitrogen than the medium duration one early in the season. It was difficult to estimate the amount ofN fixed by pigeonpea later in the season because cotton, the reference crop, accumulated more biomass than pigeonpea. Pigeonpea litter fall N contribution ranged from 58 kg ha" to 92 kg ha-l in intercropped medium and long duration pigeonpea, respectively. The average grain yield of maize obtained from plots previously planted with the sole of the long duration pigeonpea erect was higher (3940 kg ha") than from the plots that were previously intercropped with pigeonpea (3521 kg ha" ) or those that were continuously planted with maize (1833 kg ha"). This may be an indication of increased nutrient supply from decomposed litter. Intercropping of maize with long duration pigeonpea improved light, water and nitrogen use in the system more than the medium duration pigeonpea.