Enhancing Soil Fertility through Intercropping, Inoculation and Fertilizer

Grass and Legumes Intercropping for Soil Fertility

Abstract

The present study was conducted to investigate the effects of intercropping grass (Panicum
maximum) and legumes (Vicia sativa and cowpeas) alone or coupled with inoculation or fertilizer on soil
fertility. The study comprised of two field experiments conducted under rain fed conditions for two years
(June, 2005 to September, 2007) at National Agriculture Research Centre, Islamabad, Pakistan. In one
experiment intercropping (33, 50 and 67%) of grass and legumes alone as well as coupled with seed
inoculation were studied while, same set of treatments was combined with fertilizer application at the rates
of 25, 75 and 50 kg/ha (N, P2O5 and K2O) in the second experiment. Total soil N increased by 0.008% due
to symbiotic fixation in addition to plant uptake under best treatment when compared with grass alone
while, soil organic matter increased by 0.19%. After crop harvest soil N content was determined to be
higher in all the treatments of the experiment compared with growing grass alone. Legumes caused rhizobial
N fixation that caused an increase in soil N. Similarly, intercropping and inoculation increased this soil
characteristic that was found to be non-significant in the first crop but later on became significant, especially
when intercropping of grass with legumes after seed inoculation was investigated or fertilizer was
supplemented to the crops. Thus, not only grass used the symbiotically fixed N by companion legumes
but also enhanced the soil N content. The effect of fertilizer was not measurable statistically in case of soil
organic matter. This parameter, in general, was not affected significantly when assessed after first crop
harvest. Nevertheless, legumes alone or intercropped within grass increased this important soil constituent.
Inoculation proved further beneficial in this regard but combination of intercropping (especially 67%)
either with seed inoculation or application of fertilizer was found as the best technique for increasing soil
organic matter.