Rotational effects of grain legumes on maize performance in the Rift Valley Highlands of Kenya

Abstract

High fertiliser costs and declining soil fertility are'among the key factors contributing to low crop yields in Kenya. The contribution of five legumes grown in the short-rains season to soil nitrogen status and performance of a succeeding maize (Zea mays L.) was studied in an experiment at Njoro and Rongai within the Rift Valley Highlands of Kenya, from 1997 to 1999. Treatments included a weedy fallow, five grain legumes and maize (H513) grown during short-rains season followed by maize in the April-August long-rains season. The legumes were chickpea (Cicer arietinum L.), field bean (Phaseolus vulgaris L.), soybean [Glycine max(L.) Merril], garden pea (Pisum sativum L.), dolichos [Lablab purpureus (L.) Sweet]. The crop residues and vegetation of the weedy fallow were incorporated in the soil during seedbed preparation for the long rains season. The maize test crop was supplied with three levels of nitrogen, 0,30, and 60 kg ha-' as main factor whilst fallow management options were allocated as sub-factors in a split-plot treatment arrangement of a randomised complete block design replicated three times. Results show improved soil N status following legumes, with dolichos giving highest available N. Grain yield in maize succeeding legumes was 2468% higher than maize succeeding weed fallow. In the absence of N fertiliser input, maize succeeding dolichos gave 20-40% higher yield than maize after weed fallow treated with recommended 60 kg N ha-' fertiliser rate. The study has demonstrated that the use of grain legumes, particularly dolichos in rotation with maize, is a viable and preferable option to weedy fallows and maize-maize sequences.

Lablab effect on soil properties and subsequent maize-cowpea intercrop

“…This finding did not however support earlier reports (Cheruiyot et al, 2001;Ewansiha et al, 2008). This may be due to the short fallow period of one year used in the present study compared with the two-year fallow reported by Ewansiha et al (2008).…”

“…In addition, the fodder yield of lablab was low compared to those earlier reported (Ewansiha et al, 2008). The soil improvement potential of lablab is related to the biomass (Cheruiyot et al, 2001).…”

“…This finding is in agreement with previously reported values of 4-18 % for legumes in northern Nigeria (Carsky et al, 1999). Among several legumes studied, Cheruiyot et al (2001) reported highest increase in soil N in lablab plots, which was due to high residue quality. Ewansiha et al (2007) reported up to 184 kg N ha -1 for lablab shoot.…”

“…Ewansiha et al (2008) reported that amount of rainfall can improve or adversely affect lablab performance depending on whether lablab is early or late maturing. According to Cheruiyot et al (2001), maize is produced with high rainfall (300-600 mm) whereas lablab and cowpea are produced with the low rainfall (250 -400 mm) in Kenya.…”

“…One strategy that may help in improving the productivity of maize-cowpea intercrop under low soil fertility is to combine the use of residual nitrogen from nitrogen fixing legumes and inorganic fertilizer. Previous studies (Cheruiyot et al, 2001;Ewansiha et al, 2008) showed that soil N status and yield of maize improved following the growing and incorporation of lablab residues. Adding N fertilizer to plots formerly grown to lablab enhanced the productivity of subsequent maize.…”