Effects of Phosphorus and Cassava-Soybean Intercrop on Soybean Nodulation and Cassava Yield in South-Kivu, Democratic Republic of Congo

Abstract

Declining land productivity and land fragmentation/scarcity associated with war and conflicts are major problems facing the small-holder farmers in Eastern Democratic Republic of Congo. The soils have low and declining soil fertility and the situation is further exacerbated by the civil war which causes displacement leading to concentration of the population in small pieces of land. Of the soil fertility related nutrients, low available phosphorus has been identified as one of the most limiting macro-nutrients to agricultural production. In Eastern Democratic Republic of Congo, cassava is priority food and cash crop and is usually intercropped with other crops. However, due to low technological know-how of the smallholder subsistence farmers on appropriate agronomic practices and soil fertility input use, agricultural productivity low. Hence, the major objective of this study was to evaluate the effect of phosphorus application on cassava intercropped with soybean productivity. The study was carried out in two locations of Eastern DR Congo, Kabare and Uvira The field experiment was laid out in a full factorial design. The factors were: cropping system at three levels (sole cassava, sole soybean and cassava-soybean intercrop) and phosphorus (P2O5) application at three levels (0, 45.8 and 91.6 Kg P ha-1). 91.6 Kg P ha-1 application significantly (p<0.05) increased soybean grain and cassava root yields; in Kabare cassava root yield increased by 50.58% in the pure stand and 70.11% in the intercropping while in Uvira, by 43,11% in the pure stand and 55,82% in the intercropping. Soybean grains yield increased by 50.34% (Kabare long rain), 64.89 (Kabare short rain), 39.16% (Uvira long rain), 56.16% (Uvira short rain) in pure stand compared to 24.42% (Kabare long rain), 19.23% (Kabare short rain), 18.36% (Uvira long rain), 30.17% (Uvira short rain) t ha-1 in intercropping. Yield decreased in the intercropped soybean by 23.8 % in Kabare short rain and 39.55 % compared to sole soybean productivity in Uvira short rain, probably as a result of the competition with cassava. Soybean contributed less to the total land equivalent ratio (LER) (0.73 in Kabare long rain, 0.66 in Kabare short rain, 0.72 in Uvira long rain and 0.77 in Uvira short rain) than cassava 0.74 in Kabare long rain, 0.80 in Kabare short rain, 0.76 in Uvira long rain and 0.93 in Uvira short rain), this means that the beneficial effect of soybean on cassava was greater than the beneficial effect of cassava on soybean. Aggressivity values of soybean were negative (-0.18 in Kabare long rain, -0.20 in Kabare short rain, -0.17 in Uvira long rain and -0.18 in Uvira short rain) indicating that soybean was dominated by cassava in both locations However soybean intercropping with cassava Benefit Cost Ratio value was high than the pure soybean in both locations (2.18 in Kabare and 1.72 in Uvira). The results showed that soybean intercropped with cassava is therefore recommended in the land constraint areas to maximize land profitability and protein production.