Improved production systems for common bean in south-central Uganda: I. Liddugavu soil, II. Limyufumyufu soil

Common bean (Phaseolus vulgaris L.) is the most important source of dietary protein in Uganda but current grain yields are extremely low. Beans are produced on a variety of soils in south-central Uganda but the two most important soils for bean production are the highly weathered Limyufumyufu (Ferralsol) and the relatively fertile Liddugavu (Phaeozem) soils. These two soils vary in level of pH and fertility and therefore must be managed appropriately. Beans managed under conventional systems have a yield gap of about 75% due to poor agronomic practices, soil infertility, lack of seed from improved cultivars, moisture stress, weed competition, and damage caused by pests and diseases. The objective of this study was to compare the productivity and net profitability of four bean cultivars grown under three management systems on Limyufumyufu and Liddugavu soils in Masaka District, Uganda. The experiment was designed as a randomized complete block in a split-plot arrangement. Management system was the whole-plot factor and included the Conventional Farmer (CFS), Improved Farmer (IFS), and High Input systems (HIS). Management systems differed for seed fungicide treatment (no vs. yes), seeding density (10 vs. 20 seed m-2), plant configuration (scatter vs. rows), fertilizer applications (P, K, Ca, Mg, Zn, and S), rhizobium inoculation (no vs. yes), pesticide applications (no vs. yes), and frequency and timing of weeding. Subplots were four bush type common bean cultivars that differed for resistance to foliar pathogens. Increasing management level, independent of rainy season, and planting bean cultivars tolerant to common bean diseases improved bean grain yield.\nOn the Limyufumyufu soil, there were only grain yield differences between cultivars in the 2015A season; NABE 14 had the greatest grain yield (772 kg ha-1), 168% greater than NABE 15 (288 kg ha-1). The HIS with NABE 14 (1274 kg ha-1), the HIS with NABE 4 (1225 kg ha-1), and the IFS with NABE 14 (1025 kg ha-1) were the best management system × cultivar combinations for grain yield. The increased yields for these management system × cultivar combinations were likely due to the cultivars' greater host plant resistance to several bean diseases and tolerance to low soil fertility. The economic return to labor and management was only profitable for the CFS ($40 ha-1), and no differences were observed between cultivars. Additionally, both rainy seasons resulted in a net loss.\nOn the Liddugavu soil, mean grain yield was greater in the HIS (1275 kg ha-1) than in the IFS (818 kg ha-1) and the CFS (593 kg ha-1). Across management systems, disease resistant NABE 14 had greater grain yield (1212 kg ha-1) than NABE 15 (668 kg ha-1), K132 (803 kg ha-1), and NABE 4 (899 kg ha-1). The HIS with NABE 14 had the greatest grain yield (1772 kg ha-1). The increase in yield for NABE 14 was likely due to its greater host plant resistance to several bean diseases including angular leaf spot, bean common mosaic virus, and root rots. The economic return to labor and management resulted in many net losses in the 2015A season, except when planting NABE 14. Over both seasons, the greatest management system × cultivar combination was the HIS with NABE 14 ($559 ha-1).\nAll inputs and seed of bean cultivars used were obtained locally, except the rhizobia, suggesting that increased yields are obtainable by farmers under both soils, especially when utilizing NABE 14 under improved management practices with increased inputs. However, increased profits are only obtainable under the Liddugavu. The greater level of infertility and need for higher rates of nutrients for enhanced bean production on Limyufumyufu resulted in poor yields and poor economic returns to labor and management. The need for inputs was too great for Limyufumyufu and the value of bean was too low to recover the investment for all improved management system combinations.