Cover Crops Affecting Soil Water Storage Under No-Till.

We have evaluated the water storage on a clayey Rhodic Hapludox as a function of cropping systems under long-term no-till, in Botucatu, São Paulo, Brazil, a region with typically dry winters. The plots planted in the fall/winter were Congo grass (Brachiaria ruziziensis), grain sorghum (Sorghum bicolor) and a mix of both. In the spring, pear millet (Pennisetum glaucum), forage sorghum (Sorghum bicolor) and indian hemp (Crotalaria juncea) were planted in the sub-plots. Soybean (Glycine max (L.) Merril) was the summer crop. Readings of volumetric water content were taken throughout the last spring cultivation by a capacitance probe (model Diviner 2000) and soil water storage (SWS) was calculated to a depth of 0.8 m. The variation of the water storage showed a well-defined pattern, so that differences among the systems were maintained throughout the spring cultivation. Most of the results may be explained by direct effect of spring crops and of straw left by fall/winter crops. In the Congo grass plots, SWS was lower in indian hemp subplots. Congo grass was the fall/winter crop that left the greatest amount of straw, and for that, probably consumed more water. However, that was not a limiting factor, and all spring crops produced more dry matter when grown after Congo grass. Since the spring crops did not differ in the production of dry matter, we may suppose that the indian hemp was less efficient in storing water in the soil, either by using more or allowing greater loss. The least amount of fall/winter straw was left by grain sorghum, which resulted in the lower dry matter production of spring crops. In that case, the lowest SWS occurred at the pear millet subplots, which indicates pear millet water storing efficiency decreases as its dry matter production decreases. Forage sorghum, which produced the same amount of dry matter as indian hemp and pear millet, did not show the lower SWS in any of the systems, which may indicate it is an efficient crop in water usage and storage.