Optimum Crop Water Application as Affected by Uniformity of Water Infiltration¹

Abstract

Economic analyses of irrigated agriculture stress that yield levels which maximize profits can be attained with less water than maximum yields. A premise of such analyses is that irrigated soils have perfectly uniform rates of infiltration. A general method for evaluating the effects of nonuniform infiltration rates on optimal levels of water application is developed. Empirical analyses of the implications of non‐uniform infiltration rates on optimal levels of applied water, yields, and profits are reported for corn (Zea maysL.) and cotton (Gossypium hirsutumL.). The results are critically influenced by the nature of the water yield relationships postulated for these crops. For corn, where excessive water applications apparently have no effect on yield, nonuniform conditions reduce yield and profit. These outcomes can be offset by increasing water applications and optimal levels of applied water increase as the degree of uniformity declines. For cotton, nonuniformity leads to decreases in yields and profits that cannot be offset by increased water applications. This is attributable to the apparent sensitivity of cotton yields to excessive applications of water. For both crops, increases in the price of water provide little incentive to improve the uniformity of infiltration. The results demonstrate that conventional economic analyses which ignore infiltration uniformities, underestimate optimal levels of applied water, often substantially.

Uniformidade da lâmina de irrigação, da umidade do solo e da produção da cultura do feijoeiro, espacialmente referenciadas

“…Acima daquele nível, no entanto, isso não se verifica. Letey et al (1984) analisam conceitualmente essa relação. Segundo eles, em culturas pouco sensíveis ao encharcamento, quando as lâminas aplicadas são insuficientes, menor uniformidade leva a maiores retornos econômicos, uma vez que pelo menos parte da área receberia água suficiente, ao contrário do que ocorreria numa irrigação de alta uniformidade.…”

“…Segundo Libardi et al (1996), o desvio padrão é particularmente recomendável como estatística de avaliação da variabilidade, pois possui a unidade original dos dados. Porém, a utilização do desvio padrão para comparação de duas propriedades diferentes é inadequada, visto que as unidades são diferentes, necessitando-se, nesse caso, de uma medida relativa da variabilidade.…”

“…Libardi et al (1996) apresentam ferramentas para a análise de dados distribuídos no espaço, tais como o diagrama de ramos e folhas. Outra ferramenta muito útil é o gráfico "box-plot", conforme afirmam Isaaks e Srivastava (1989).…”

Quality and maximum profit of industrial tomato as affected by distribution uniformity of drip irrigation system

“…The interdependency between total yield and °Brix, and the decreasing quality of marketable fruits with high levels of applied water, will require the optimisation of tomato water application. Evaluations by Letey et al (1984) and Sammis & Wu (1985) of crop water application and the effects of optimal levels of applied water on profitability of irrigation suggest taking into account the distribution uniformity of the irrigation system.…”

“…Thus, field-level production functions may differ from those estimated assuming uniform irrigation. Letey et al (1984) presented a very flexible method to integrate crop-water production functions with a spatial variability of applied and infiltrated water. In this study we use the method to analyse the production of the industrial tomato, expanded to incorporate the analysis of the technological quality of the harvested product.…”