Effects of planting density and weeding regimes on forage and grain yield of maize
Maize is a major food and forage crop in Kenya and planting density and weeding regime influence yield. The effects of weeding regimes and maize planting density on maize forage, grain yield and quality were evaluated during the 200112 short rains and long rains of2002 at Kenya Agricultural Research lnsitute, Muguga in Central Kenya. Weeding regimes were weed free (WI), weedy (W2), herbicide (W3) and hand weeding twice (W4). Maize densities were 9 (01) and 18 plants m-2 (02) intercropped with beans. Maize was thinned at 98 OAE at tasseling stage and assessed for forage yield and quality. Stover and edible weeds biomass yield and quality were also assessed. Soil moisture content down the profile, PAR interception, weed density, maize height and rate of tasseling was determined gradually over the season. Maize yield and bean biomass was also determined. The collected data was anaJysed using GENST AT software and their means separated with LSD at P = 0.05. Percent interception of photosynthetically active radiation (PAR) was significantly higher in 02 than in OJ before thinning time but was significantly higher in 01 than in 02 after thinning in both seasons. Interception of PAR was significantly higher in W2 compared to WI, W3 and W4, which were similar in both experiments. Soil moisture content was significantly lower in W2 but similar in WI, W3 and W4. 02 had significantly lower soil moisture content than Dl in season two through out the season. Thinnings biomass was higher where weeds were controlled and least in the weedy regime in both seasons. Thinnings biomass was significantly higher in 02 than 01 in both seasons and 01 had significantly higher maize grain yield than 02 in both seasons. Stover biomass was significantly higher in 0 J than 02 in season one but was similar in season two. Total forage biomass from Dl was same as in D2 in season one whereas in season two was significantly higher in D2 than Dl. Beans performed poorly due to low planting density and shading effects due to maize in both seasons. The tasseling rate was significantly lower in D2 than DI while W2 had significantly lowest tasseling rate as compared to WI, W3 and W4, which had similar tasseling rate in both seasons. Maize plants were significantly short in W2 compared to WI, W3 and W4, which were similar. They were also shorter in D2 than in DI in both seasons. Total weed biomass at 126 DAE was significantly higher in W4 than in W3 and in DI than in D2 in both seasons. The cattle-edible weed biomass at the end of the two seasons was at least 55 % of the total. Thinnings had significantly higher digestibility (76 %) and crude protein (7 %) than stover. Two times hand weeding (W4) was two to three times more expensive than using herbicide (W3). Weeds competed for light and water leading to reduced thinnings, stover and grain yield but increased weed biomass, which was significantly lower than maize biomass in the weeded plots. High maize density increased intraspecific-competition (of maize in the hills) for water and light before thinning time (98 DAE) and significantly reduced plant height, tasseling rate and grain yield. Hand weeding is labour intensive and thus led to increased expenses than herbicide use. Planting maize at high density significantly increased forage quality and quantity, and overall light capture especially before thinning, but reduced weed biomass and grain yield.