Assessment of weed infestation and economic returns of maize/cowpea intercrop under different tillage systems in northern Ghana

The cost of crop production is mostly attributed to soil tillage and weed control. Against this background,. a field experiment was conducted at Nyankpala in the northern Ghanaian savanna ecology in 2000 and 2001 to assess the ~ffects of tillage and cropping systems (CRPSYT) on ,"eed infestation and economic returns of maize (Zea .nays L) intercropped with cowpea (Vigna unguiculata L Walp). The results showed that the tractor-ploughed conventional tillage system (Con) and bullock plough (BP) with tillage depths more than 12 cm significantly (P<0.05) increased grain yields of both crops and also significantly reduced weed score, weed count, and the subsequent weed dry matter, probably through deep burying of weed seeds as compared to hand hoe (HH) and zero tillage (ZT) practices. Tillage systems did not influence weed flora, but cropping systems increased the grass composition in maize to about 70 per cent and significantly decreased the broad leaf weeds. The reverse situation was observed in the cowpea and the maize/cowpea intercrop. The predominant grass weed species found on the field were Eleusine iirdica and Digitaria spp. , while the broad leaf weeds were Amaranthus spinosis and Tridax procumbens. The highest cost was incurred under ZT due to high cost of herbicides and labour for spraying while the least was in HH, but the highest net benefits and the highest benefit-cost ratio (BCR) were recorded under BP. The maize component yielded higher BCRs in the sole and the intercrops. However, poor rainfall distribution had negative impact on the yield of both crops, resulting in negative BCRs in the inter-row cropping systems in both years. ~ RESUME KOMBIOK, J. M. , SAFO, E. Y. , QUANSAH, C. & IBANA, S. : Evaluation de l'infestation de mauvaises herbe et les rentabilites economiques de mai"s/do/ique en /ignes alternantes sous les differents systemes de labour au nord du Ghana. Une part importante du cout de production de culture est attribuee au labour du sol et au desherbage. Dans ce contexte, une experience au terrain s'est deroulee IINyankpala dans I'ecologie de la savane au nord du Ghana en 2000 et 2001 pour evaluer les effects de labour et les systemes de culture (SYTCUL) sur I'infestation de mauvaise herbe et les rentabilites economiques de mars (Zea mays L) seme en lignes alternantes de dolique (Vigna unguiculata L. Walp). Les systemes de labour se composaient de labour de tracteur comme systeme de labour conventionnel (Con), labour II breufs (LB), houe II main (HM), et labourage zero (LZ); alors que les systemes de culture consistaient de mais seul, dolique seule, systeme de culture de mais/dolique inter-ligne et une jachere en 2000 avec la jachere etant remplace par la systeme de culture de mars/dolique intra-ligne en 2001. Les resultats revelaient que Con et LB avec les profondeurs de labour de plus que 12 cm augmentaient considerablement (P < 0.05) les rendements de grain des deux cultures et egalement reduisaient considerablement nombre de mauvaise herbe, Ie compte de mauvaise herbe et la matiere seche suivante de mauvaise herbe probablement II cause de I'enterrement profond de graines de mauvaise herbe comparee aux pratiques de labourage de HM et LZ. Les systemes de labour n' ont pas influence la flore de mauvaise herbe mais les systemes de culture augmentaient la composition des graminees en mais II 70 % alors qu'ils diminuaient considerablement les mauvaises herbes II feuille large. La situation inverse etait observee en dolique et en mars/dolique en lignes alternantes. Les especes des graminees herbeuses prMominantes rencontrees sur Ie terrain etaient Eleusine indica et Digitaria spp. alors que Provisional communication. Received 30 Sep 02; revised II Feb 03.