Changes in some physical properties of a typic haplorthox in southern Brazil under no-tillage crop rotation systems

The assessment of the impacts of different crop rotations on soil physical properties is needed to identify those with the potential to improve such properties which enhance crops´ responses to soil nutrients. The effects of eight crop rotations on physical properties of a Rhodic Ferralsol (Typic Haplorthox) were assessed in Palmital, Svo Paulo, Brazil, using a randomized complete block design with three replications of each treatment. The study lasted for five years (1985 –1990). The crop rotations, planted during the winter from 1985 to 1987, were mucuna, pigeon pea, rye, oat, pisum, wheat, crotalaria and black oat. In 1988 wheat was planted on all plots and from 1989 to 1990, lathyrus, lupin, rye, oat, lupin + black oat, wheat, crotalaria and black oat were planted. The summer crops were maize and soybean. In all treatments and taking the average of all the soil horizons, lupin+black oat and lathyrus produced the lowest bulk density in both maize and soybean plots. When the ranking of the performance of these crop rotations was performed, the order in the maize plots was lupin+black oat > rye > lathyrus > lupin/wheat > oat > crotalaria/black oat. On soybean plots the order was lathyrus > lupin > lupin+black oat > rye > oat > crotalaria > black oat > wheat. It is evident that for the summer crops, lupin+black oat, rye, lathyrus and lupin were consistent in improving these soil physical properties and are therefore, better than the rest of the rotation crops in moderating these properties. Even though there was low improvement in OM content of the soil, OM moderated very significantly bulk density (r =0.602**) and saturated hydraulic conductivity (Ksat) (r = 0.674**) under soybean plots. However, macro-porosity (Pe) had positive improvement in Ksat (r = 0.684**) under maize of all the physical properties measured. Longer lasting crop rotations may produce more positive influences of OM on these soil physical properties. Keywords: Water holding capacity; Aggregate stability; Saturated hydraulic conductivity; Bulk density; Organic matter; Maize; Soybean. Agro-Science Vol. 3 (2) 2006: pp. 1-1