Effects of tillage and cropping systems on yield and nitrogen fixation of cowpea intercropped with maize in northern Guinea savanna zone of Ghana

English

Published information is scanty on the response of crops in mixed cropping systems to the various tillage systems practised by farmers in the northern savanna zone of Ghana. A field experiment assessed the yield and nitrogen (N) fixation of cowpea (Vigna unguiculata (L.) Walp) intercropped with maize (Zea mays L.) on four different tillage systems at Nyankpala in the Northern Region of Ghana. The experiment was laid in a split-plot design with four replications. The main factor was tillage systems comprising conventional (Con), bullock plough (BP), hand hoe (HH) and zero tillage (ZT). The sub-factor was cropping systems (CRPSYT) which consisted of sole maize, sole cowpea, maize/cowpea inter-row cropping system, and bare fallow in 2000. The last-named was replaced by maize/cowpea intra-row cropping system in 2001. The results showed that Con and BP, which produced over 10 cm plough depth, significantly reduced soil bulk density that favoured significant (P<0.05) increases in the number of nodules per plant and nodule weight. However, ZT with the highest bulk density significantly (P<0.05) reduced the N content in both crops, but phosphorous (P) and potassium (K) contents were unaffected by tillage systems. Percent N fixed by cowpea at 8 weeks after planting (WAP) was not different between Con and BP, but both were significantly lower (P<0.05) than in the HH and ZT treatments. Grain yields of maize and cowpea on Con and BP were similar but significantly higher (P<0.05) than on HH and ZT, which were also not different. Cropping systems had no significant effects on nodule number per plant, nodule weight, and N, P and K contents in both crops; but N, P and K yields and also percent N fixed by cowpea were significantly higher (P<0.05) in the sole than in the intercrops. Grain yields of both crops were also significantly higher (P<0.05) in the sole than in inter- or intra-row cropping systems. The land equivalent ratios (LERs) of both mixtures were not significantly different, but each was greater than one (LER>1). The LERs ranged from 1.43 to 1.79 in 2000, and from 1.23 to 1.24 in 2001 for Con and ZT, respectively. These indicate 33 and 52 per cent mean increases in productivity of cowpea and maize, respectively, over their pure stands across the 2 years. However, grain yields of both crops from the inter- and intra-row cropping systems were not different.

Kombiok, J. M.; Safo, E. Y.; Quansah, C.