Patterns in phosphorus and corn root distribution and yield in long-term tillage systems with fertilizer application.

摘要

The distribution of phosphorus in the soil profile as a function of soil tillage, fertilizer management system and cultivation time is strongly related to root distribution. As the dynamics of this process are not well understood, long-term experiments are useful to clarify the cumulative effect through time. The study evaluated an 18-year-old experiment carried out on Rhodic Paleudult soil, located in Rio Grande do Sul state - Brazil, with cover crops (black oat and vetch) in the winter and corn in the summer. In the 0- to 20-cm layer, the amounts of clay, silt and sand were 22, 14, and 64 g kg-1, respectively. This layer had a mean slope of 3%. The mean local annual rainfall is 1440 mm. The climate is subtropical with a warm humid summer (Cfa), according to the Koeppen classification. The treatments consisted of three soil managements (conventional tillage, no tillage and strip tillage) and three application modes (broadcast, row and strip) for triple superphosphate and potassium chloride fertilizers. Data for phosphorus and root distribution in the soil from the 1989/90, 1999/00 and 2006/07 growing seasons were used. Phosphorus stratification occurred through time, irrespective of soil and fertilizer management, mainly in the 0- to 5-cm layer. The tillage and fertilization systems promoted significant differences in the Pi and Pt fractions up to a depth of 20 cm. For the Po fraction, significant differences were found only in the 0- to 5- and 15- to 20-cm layers. Inorganic phosphorus accumulated in the fertilized zone (0-10 cm), with higher intensity in the no-tillage system under row fertilization with values around 150 mg dm-3. Root distribution presented a strong positive relationship with phosphorus distribution, exhibiting redistribution in the soil profile through time. This redistribution was accompanied by increases in organic phosphorus and total organic carbon content. Corn grain yield was not affected by long-term tillage systems.