Maize (Zea mays L.) is an important smallholder crop in Uganda. Yields are low because of low soil fertility and little fertilizer use. Yield response to nutrient application and economically optimal rates (EOxR, where x = N, P, or K) and N use efficiency (NUE) were evaluated. Twenty‐two trials were conducted in four agroecological zones. Yield was consistently increased with N application. Mean maize yield with no N applied (N0) was 1.79 Mg ha−1 and increased by 120% with N application. Mean EONRs were 45 to 24 kg ha−1 N with fertilizer use cost to grain price ratios (CPs) of 10 to 30. With N applied, the mean increase in yield due to P application was 0.28 Mg ha−1 and mean EOPRs were 9 to 1 kg ha−1 P with CPs of 10 to 50. Yield was not increased with K application. Profitability was greater for N than P application. Mean aboveground biomass N with 0 and 150 kg ha−1 N applied was 46.3 and 94.3 kg ha−1, respectively. Mean N concentration and N harvest index at the EONR were 1.60 and 63.8%, respectively, and higher than for N0. Mean recovery efficiency, partial factor productivity, and agronomic efficiency declined with increasing N rate and were 66%, 86 kg kg−1, and 41 kg kg−1, respectively, at the EONR. Fertilizer N use can be very profitable, with high NUE, for smallholder maize production in Uganda, and the financial capacity of smallholders to use fertilizer will increase with reduced CP.

16This paper reports on a Participatory Learning and Action Research (PLAR) process that 17 was initiated in three villages in Eastern Uganda in September 1999 to enable small-scale farm-18 ers to reverse nutrient depletion of their soils profitably by increasing their capacity to develop, 19 adapt and use integrated natural resource management strategies. The PLAR process was also 20 used to improve the participatory skills and tools of research and extension personnel to sup-21 port this process. The farming systems of the area were characterised for socio-economic and 22 biophysical conditions that included social organisations, wealth categories, gender, crop, soil, 23 agro forestry and livestock production. Farmers identified soil fertility constraints, their indi-24 cators, and causes of soil fertility decline, and suggested strategies to address the problem of 25 soil fertility decline. Soil fertility management diversity among households indicated that most 26 farmers were not carrying out any improved soil fertility management practices, despite pre-27 vious research and dissemination in the area. Following the diagnosis stage and exposure visits 0308-521X/$ -see front matter Ó

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Sorghum [Sorghum bicolor (L.) Moench] is important for smallholder production in semiarid parts of Uganda. Grain yields are low because of low soil fertility. Little fertilizer is used. Yield response to N, P, and K application, economically optimal rates for N, P, and K (EONR, EOPR, and EOKR, respectively), and N use efficiency (NUE) were evaluated at 11 site‐seasons. Mean sorghum yield with no N applied (N0) was 0.69 Mg ha−1 and was consistently increased by a mean of 230% with N application. Mean EONRs were 34 to 18 kg ha−1 N with fertilizer use cost to grain price ratios (CPs) of 10 to 30, respectively. Mean EOPRs were 11 to 2 kg ha−1 P with CPs of 10 to 50, respectively. Sorghum did not respond to K application. Net economic returns were greater for N than P application. Mean aboveground biomass N with 0 and 90 kg ha−1 N applied was 31.3 and 75.9 kg ha−1, respectively. Grain N concentration, N harvest index, and internal NUE at the EONR were 1.67%, 53.2%, and 31.8 kg kg−1, respectively, and higher than for N0. Mean recovery efficiency, partial factor productivity, and agronomic efficiency declined with increased N rate and were 135%, 79 kg kg−1, and 52 kg kg−1, respectively, at the EONR. The profit potential of fertilizer N use is high for smallholder sorghum production in Uganda. Policy interventions to reduce fertilizer cost and improve grain marketing efficiency will enable smallholders to increase fertilizer use for substantial increases in sorghum production.

Grain sorghum [Sorghum bicolor (L.) Moench] is an important food crop of semiarid sub‐Saharan Africa. Crop yields are generally low, partly due to low soil fertility. Research was conducted with farmers to evaluate, soil fertility management practices in sorghum‐based cropping systems including: mucuna [Mucuna pruriens (L.) DC.] fallow; cowpea [Vigna unguiculata (L.) Walp.] rotation with sorghum; animal manure application; N and P fertilizer application; and reduced tillage. Four studies, comprised of 142 on‐farm trials, were conducted at three locations over 3 yr in drought‐prone parts of eastern Uganda. Mucuna on average produced 7 Mg ha−1 of aboveground dry matter containing 160 kg N ha−1 across the three locations. Application of 2.5 Mg ha−1 of manure and of 30 kg N plus 10 kg P ha−1 increased grain yield by 1.05 and 1.30 Mg ha−1, respectively. A combination of 2.5 Mg ha−1 manure with 30 kg N ha−1 increased grain yield by 1.50 Mg ha−1 above the control (1.1 Mg ha−1). The increase in sorghum grain yield in response to 30 kg N ha−1 alone, to a mucuna fallow, and to a rotation with cowpea was 1.15, 1.55, and 0.82 Mg ha−1, respectively. These soil fertility management practices, as well as reduced tillage, were found to be cost effective in increasing sorghum yield in the predominantly smallholder agriculture where inorganic fertilizer was not used much. On‐farm profitability and food security for sorghum production systems can be improved by use of inorganic fertilizers, manure, mucuna fallow, sorghum–cowpea rotation, and reduced tillage.