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We investigated under field and laboratory conditions the decomposition and nutrient release from mixed leaf litters of Faidherbia albida (Del) A. Chev. and Vitellaria paradoxa C.F. Gaertn. f. in the south-Sudanese zone of West Africa. Litterbags containing F. albida and V. paradoxa litters in varying proportions were placed on the soil surface and buried in plots receiving the following treatments: no fertilizer (control); nitrogen; phosphorus as Triple Superphosphate (TSP); and phosphorus as rock phosphate from Burkina Faso (BP). At each litterbags collection date, the undecomposed litter from each species was separated, and its remaining mass, nitrogen, phosphorus and potassium contents were determined. F. albida decomposed faster (k-values ranged from 0.060 to 0.171 week -1 ) than V. paradoxa (k-values ranged from 0.020 to 0.056 week -1 ) and released more nutrient than V. paradoxa. Mixing litters accelerated the decomposition rate of both F. albida and V. paradoxa litter. Decomposition was faster in the nitrogen and TSP plots than in the control and BP plots, and buried litter decomposed more rapidly than surface litter Also under laboratory conditions, F. albida litter decomposed more rapidly than V. paradoxa litter as the microbial specific growth rate were 0.135 h -1 and 0.069 h -1 , respectively. Results indicated that mixing litters of contrasting qualities may be a promising option to regulating decomposition/mineralization rates from organic material.

Stochastic dominance was used to determine the risk characteristics of phosphate fertilization of millet, sorghum and maize with commercial NPK fertilizer, rock phosphate and partially acidulated rock phosphate in Burkina Faso. On‐farm‐trial data from 1989, 1990 and 1991 in three rainfall zones was used. The analysis shows that among the four treatments tested, commercial NPK fertilizer has the most desirable risk characteristics. It is acceptable to risk averse decision makers for all three crops in all rainfall zones. The no‐fertilizer control is dominated by the fertilizer treatments. The rock phosphate treatments have higher yields and in certain cases higher returns than the no fertilizer control, but those benefits are less sure than for the soluble commercial fertilizer. The distributions of cash returns to rock phosphate treatments are rarely significantly different from those of the control. Rock phosphate treatments never dominate the commercial fertilizer treatment. If farmers have a choice between commercial fertilizer, rock phosphate and partially acidulated rock phosphate, at current prices most of those who use fertilizer would choose the soluble commercial product. If the availability of commercial fertilizer were limited (e.g. by lack of hard currency), some farmers would use rock phosphate—especially the partially acidulated product. Stochastic dominance permitted a timely and detailed analysis of risk inherent in phosphate fertilizer alternatives. Because on‐farm‐trails involve a modest number of alternatives, pairwise stochastic dominance comparisons are feasible. The stochastic dominance analysis permits researchers to communicate to extension staff and policymakers not only the degree of risk, but also something about the characteristics of the crop response that contribute to risk. The key to effective use of stochastic dominance is careful study of the distributions and understanding why a technology is dominated or is potentially acceptable to risk averse decisionmakers.

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