Sources and Rates of Phosphorus in a Cultivation System Integrating Crop and Pasture Production in the State of Parana

The integration of crop and pasture production (ICP) within the same area, using no-tillage cultivation systems, is becoming popular in Brazil due to its agronomic advantages. Phosphorus is a key nutrient in these systems and soils in the state of Parana are generally low to medium in bioavailable P. The main purpose of this research is to evaluate the effects of P rates and sources (water-soluble and water-insoluble) on soil quality, plant mineral nutrition, forage, grain, and meat yields in an integrated crop-livestock system under no-till. The site has been under no-till for five years. Treatments include three sources of P [triple superphosphate (TSP), magnesium thermophosphate (MTP), and Arad reactive rock phosphate (RP)] and three rates of P (60, 120, and 180 kg total P₂O₅/ha), with all sources applied prior to seeding the winter crop. The trial also included a control, with no P applied, and three treatments supplying each source at 90 kg P₂O₅/ha applied prior to seeding the spring-summer crop.

The results for winter black oats (winter crop) showed response to P, in terms of dry-matter yield, when TSP and MTP were applied, although TSP had an advantage. No response to RP was observed, most likely due to its low initial solubility. For the following corn crop there were responses in P leaf concentration for all P sources applied prior to seeding the winter crop (i.e,, linear responses for TSP and MTP, and a quadratic response for RP). However, no response was observed in terms of corn crop yield (average of 11,716 kg/ha). This lack of yield response, even in a soil with medium P status, is most likely related to: 1) high water availability for corn in this cropping season, which favored P diffusion to the plant roots; 2) high soil organic matter leading to lower amounts of soil P fixation; and 3) high P cycling in ICP systems resulting in more bioavailable P for the summer crop (in this case corn). This is a long-term experiment and new results will be available over time. Brazil-55