Exploring legacy P with cover crops in long-term: change in grain yield, P dynamics and soil enzymatic stoichiometry

Author(s)

João Henrique Silva da Luz

• Document type: Master's Dissertation
• Press: Piracicaba.
• Institution: Universidade de São Paulo (USP). Escola Superior de Agricultura Luiz de Queiroz (ESALA/BC)
• Defense date: 2023-05-10

Examining board members

Paulo Sergio Pavinato; Leônidas Carrijo Azevedo Melo; Tales Tiecher

• Advisor: Paulo Sergio Pavinato

Abstract

The frequent use of phosphate fertilizers may result in the accumulation of P in soils (also known as legacy P) in organic (Po) and inorganic (Pi) forms. However, most of these forms of P are not available for absorption by cash crops. The cultivation of cover crops, in the off-season, can increase the availability of P for commercial crops because they have different P acquisition strategies that can access the soil legacy P. The objective was to investigate the effect of cover crops associated with phosphate sources on grain yield, nutrient cycling, chemical attributes, P dynamics and soil enzymatic stoichiometry in the long-term, with seven crops under phosphate fertilization and five crops exploring legacy P. The treatments were composed of five winter cover crops and one fallow, associated with two phosphate sources (simple superphosphate (SSP) and rock phosphate (RP)) and without the P inputs (Nil-P). The cover crops boosted the responses in grain yield in years with and without P application. However, it was superior in exploring legacy P. In the latter, white lupin with rock phosphate increased grain yield by 25%. The highest p uptake by the cover crops occurred with fodder radish and black oat, for N, it was white-lupin, fodder radish and black oat. However, in general, K depended on the biomass production of the cover crops. The cover crops reduced soil P-resin and K+, especially with rock phosphate, but this did not directly reflect grain yield losses. The cover crops increased agricultural sustainability by promoting increasing grain yields (soybean or corn) with or without P inputs in the system, in addition to having increased nutrient cycling and exploiting the legacy P. On average, the labile P pools were 83, 69, and 52% by labile Po for Nil-P, SSP, and RP, respectively. In labile Po there was a difference of cover plants only in Nil-P (12 years exploring legacy P), common vetch, ryegrass, and white lupin were lower than 24, 17, and 14% to the fallow. In the activity of acid phosphatase, white lupin was superior to the other cover plants and stood out in the SSP source, with 46% higher than fallow. Phosphate sources mainly modulated the effect of the cover crops on P dynamics due to differences in the total P applied. Fodder radish and black oat were the species that most exhausted these fractions of P loss labile. The cover crops regulated the microbial homeostasis predicted by enzyme stoichiometry in legacy P scenarios, and this response may be flawed according to the applied model. There has always been C limitation by the microbiota, although fodder radish, black oats, and rye have reduced this limitation. Even on high available P content, common vetch maintained N/P homeostasis and white lupin always favored P limitation, with stimuli to Pacquisition enzymatic activity. This did not occur for grasses, where the available P gradient favored N limitation, similar to fallows. (AU)

• FAPESP's process: 21/08396-7 - Phosphorus dynamics, organic matter fractions, and soil microbial activity under phosphate sources and cover crops
• Grantee: João Henrique Silva da Luz
• Support Opportunities: Scholarships in Brazil - Master