Economic and agronomic evaluation of a common bean experiment Uberaba, Minas Gerais

Com a finalidade de estudar as possibilidades de aproveitamento dos cerrados da região para o cultivo do feijão, foi analisada a influência, na produção, de cinco níveis de N e P2O5 utilizando-se um fatorial 5X5 completo. A partir dêsse esquema experimental comparou-se a eficiência de quatro outros delineamentos. Um esquema central composto mais os extremos teve eficiência equivalente ao do fatorial 5x5 completo e foi utilizado na interpretação econômica. Determinou-se a superfície da resposta dos insumos e produção e as combinações de nutrientes que resultaram nos lucros máximos. Finalmente, na última parte do trabalho foram feitas considerações sobre procedimentos alternativos do uso dos insumos face a variações dos preços do produto dos insumos.An economic and agronomic evaluation of the possibilities to produce common beans in poor "cerrado" in central Brazil was made by the use of five levels of N and P2O5. The experimental portion of the paper deals with a comparison of several types of "treatment designs", some of which are specific for estimating response surfaces. The results from one of the latter designs were used to demonstrate the general principles of agronomic economics analysis. .The results have shown that central composite plus extremes design provided information equivalent to the standard 5x5 factorial with the use of fewer resources and, therefore, was used in the economic phase of the paper. The other designs studied were small and large 3x3 factorials and central composite. To evaluate the use of N and P2O5 in the production of beans, estimates were made of the economically relevant portions of the plant nutrient input-output surface. A graphic illustration of three curves of a family of isoquants for the production of beans was made. Points of equal marginal rate or substitution of successively higher isoquants were marked by the line called isocline. Output maximization and cost minimization were determined as well as profit maximization. The return per hectare after deducting costs of applied N and P2O5 vary with the price of beans per kg. In general, optimal quantities of inputs and residual return fall as factor prices increase. However, a greater percentage of decrease occurs in residual return per hectare and in yield per hectare, as the price of P2O5 increases (with the price of N held constant). It was shown that the proper anticipation of the price of beans is important to the farmer to obtain maximum returns. He will use the most profitable combination of inputs