Doses and Application Seasons of Potassium in the Soybean-Corn Succession in Soil With Improved Fertility in the Southwest of Goiás

Soils with improved fertility indicate opportunities for more rational use of fertilizers. The objective of this study was to evaluate the management of potassium fertilization in the succession of soybean-corn in soil with improved fertility, in the southwestern region of the state, Goiás. The experiment was set in 5×3 factorial scheme, arranged in randomized blocks with four repetitions. The treatments consisted of the combination of potassium doses (0, 40, 80, 120 and 160 kg ha-1 of K2O) and seasons of application (100% of the dose in pre-planting, 100% of the dose in coverage and in installments with 50% of the dose in pre-planting + 50% in coverage). The best performance of soybean, considering grain yield, was obtained with the parceled application of 80 kg ha-1 of K2O, with production of 3.6 Mg ha-1. The highest corn production was obtained with the anticipated application of 160 kg ha-1 of K2O in soybean. In the management of potassium fertilization in improved fertility soil in the soybean-corn succession, the parceled application of 120 kg ha-1 of K2O kept the available K reserve in the soil constant when compared to its initial content.

A critical survey of investigations on the “wilting coefficient” of soils

The experiments of Briggs & Shantz led them to conclude that the “wilting coefficient” is a soil “constant” which is (a) independent of the kind of plant used as indicator, (b) independent of the conditions under which the plant was grown, and (c) directly related to several other soil constants.Subsequent research as well as an examination of their own results has shown that (c) is untrue, while (a) and (b) are substantially correct for hygrophytes and mesophytes. Earlier writers have been led to wrong conclusions regarding (a) and (b) through assuming (c) to be correct and through disregarding the particular nature of “permanent wilting” as defined by Briggs & Shantz.The fact that considerable variation is to be found between the osmotic pressure found in different plants, in different parts of the same plant and in the same part under different conditions is not at variance with conclusions (a) and (b) when properly understood.An important factor making for the substantial constancy of the “wilting coefficient” for a given soil is the extreme steepness of the curve connecting suction pressure and soil moisture content, in consequence of which differences of suction pressure of unquestionable significance from the standpoint of plant physiology give rise to differences in soil moisture content that are too small to be detected.

‘Single value’ soil properties: a study of the significance of certain soil constants: II. Studies on Natal soils

In the first paper of this series (10)1, Keen and the present writer discussed work by earlier authors on the approximate specification of the nature of a soil by a single soil constant, in place of a detailed analysis, and described experimental work designed to show the significance of a number of simple physical measurements. The chief objects of the present paper are to describe the results obtained with such measurements as applied to a number of Natal soils, and to discuss the value of some other easily obtained physical data as a means of specifying the nature of a soil. Work of this type was discussed at the International Congress of Soil Science at Washington in 1927, and it was resolved that co-operative work on an international basis should be undertaken.