Effects of Plant Density and Delayed Bean Sowing on Yields, Economic and Nutritional Perfomances of Cassava-Maize-Bean Intercrops: A Case Study in Kirimiro and Mumirwa Agro-ecological zones, Burundi

Abstract

Cassava-maize-bean intercropping systems testing effects of spacing (plant density) and bean planting date were assessed under two major Burundi agroecological zones (AEZ), Mumirwa and Kirimiro. Evaluated spacing for all three tested crops were as follows: recommended spacing (RS), RS+20 % and RS + 40 %. Bean was planted either at the same time as other two crops or with a 3-week delay. Measured parameters were intercrops’ and total yields, nutrient value (energy, proteins) and economic benefits (gross monetary values, total costs, net returns and value/cost ratio -V/C). Overall measured parameters, beans contributed more in the Kirimiro AEZ, while cassava contributed more in the Mumirwa AEZ. In the Mumirwa AEZ, cassava represented 82 % of the total yields, while bean and maize represented only 11 and 7 %, respectively. In the Kirimiro AEZ, comparative figures were 54 % for cassava, 33 % for bean and 13 % for maize. Cassava represented 64 % of the total energy yields in the Mumirwa AEZ and 20% for maize and 16 % for bean. In the Kirimiro AEZ, similar figures were 34 % for cassava, 46 % for bean and 20 % for maize. Bean contributed 77 % of the total proteins when all three crops were installed at the same time, whereas maize brought in 10 % and cassava 13 % of proteins, respectively. Bean generated 23 % more money in the Kirimiro AEZ while cassava yielded three-times more money in the Mumirwa AEZ. Overall, revenues generated through the cassava + maize + bean intercropping was two times higher in the Mumirwa than in the Kirimiro AEZ. In the Kirimiro AEZ, bean contributed for 60 % of the total monetary values and only 27 % in the Mumirwa AEZ. A similar reflexion applied to cassava indicated that it contributed to the crop yield global monetary value for 67 % in the Mumirwa AEZ and only 30 % in the Kirimiro AEZ. Maize monetary contribution to the global monetary values was 10 % in the Kirimiro AEZ and 6 % in the Mumirwa AEZ. Maize contribution across AEZ was almost insignificant because of its low yields and practiced selling prices. With a V/C ratio of 2.42, the cassava + maize + bean intercropping system was more profitable in the conditions of the Mumirwa AEZ. In the Kirimiro AEZ bean production was 60 % higher when planted at the same time as other crops than when delayed for three-weeks. Similar tendancies were observed for returns (+ 72 %), V/C (+ 34 %), energy (+ 60 %) and proteins (+ 60 %) yields. On the opposite, bean 3-week delay favored maize yield (+ 42 %), energy and proteins yields (+ 42 %). The same trends in agronomic, economic and nutritional values was also observed in the Mumirwa AEZ with lower bean and maize productions but higher cassava yields. In conclusion, all in all, more returns (+ 36 %) were obtained when all three crops were sown/planted at the same time with a V/C ratio = 2.36. In parallel, effect of crop density/spacing indicated that recommended crop spacing increased by 20 % (RS + 20 %) was more economically profitable (V/C=2.39).