Surface application of lime and fertilization with phosphorus and sulfur in a wheat-soybean cropping system under no-till

Abstract

Brazil plays a pivotal role in global food production and food security as the world's largest producer of soybean, which contributes to the global protein production. In Southern Brazil, wheat is a crop of significant importance in the wheat-soybean rotation, cultivated during the

fall-winter season. Despite Brazil's large agricultural production, which is largely based on no- till systems, there is potential to increase crop yield through more appropriate management

practices. Brazil, as it is located in regions with a tropical and subtropical climate, has highly weathered soils characterized by high acidity, low levels of exchangeable bases (Calcium (Ca), magnesium (Mg), and potassium (K)), high phosphorus (P) fixation by iron and aluminum hydroxide-oxides, and low levels of sulfur (S) mainly due to the frequent use of fertilizers without S. In no-till systems, the correcting soil acidity in subsurface layers can be challenging due to the low solubility and slow reaction of lime in the soil. Surface application of lime and fertilization with P and S in a wheat-soybean cropping system under no-till were studied in this thesis in four chapters. In the first two chapters, alternatives to improve the reaction of lime applied to the soil surface and the plant nutrition and grain yields of wheat and soybean in a no-till farming system were analyzed. In chapter 1, the effects of surface lime (SL) combined with the use of monoammonium phosphate (MAP) and elemental sulfur (ES) were investigated on soil acidity, root growth, nutrition, and grain yield of a wheat-soybean rotation under a no-till farming system. Fertilization with MAP and MAP + ES in combination with SL did not improve the response of surface liming in correcting soil acidity in the soil profile and showed similar effects compared to SL alone. The improvement of soil fertility with SL favored wheat root growth more than soybean, although it increased the grain yield of both crops. Lime resulted in an average increase in wheat grain yield of about 40% when applied alone and 74% when combined with MAP + ES. The average soybean grain yield increased by 36% with SL, regardless of the use of MAP, and MAP + ES. In chapter 2, it was investigated whether combining SL with application of single superphosphate (SSP) in broadcast (SSPB) and in-furrow (SSPF) or phosphogypsum (PG) could improve the action of lime in alleviating acidity in the soil profile, plant nutrition and grain yield of wheat and soybean under a no-till system. In this study, it was found that SL under a no-till system effectively increased soil pH, Ca and Mg contents, and base saturation, and reduced Al content and Al saturation in the soil profile up to 1 m deep in the short- and -medium term. However, SL alone was superior or equivalent to the treatments with SL + SSPB, SL + SSPF, and SL + PG. The application of SSPB, SSPF, and PG in combination with liming increased P content in the soil surface layer (0–0.10 m), with a more pronounced increase observed with the SSPB application. In the short term, 1 year after liming, the addition of PG combined with SL increased the SO4-S content in the subsoil layers (from 0.10 m to 1 m), while at 3 and 5 years after liming, there was an increase in SO4-S content with both SSP (SSPB and SSPF) and PG use, with a more pronounced effect observed with SSPB application. The cumulative wheat grain yield from five harvests increased by 40% with SL, 54% with SL + SSPF, and 70% with SL + SSPB and PG. Meanwhile, the cumulative soybean grain yield from five harvests increased by 36% with SL, regardless of the addition of SSPB, SSPF, and PG. In chapter 3, questions related to the mode of application (broadcast or in the sowing furrow) of phosphate fertilizers (MAP and SSP) in maintaining P content in the soil and responses of wheat and soybean in a no-till system were addressed. The hypothesis to be tested was that in soil with a high P level, the mode of application of phosphate fertilizers does not affect the availability of P in the soil as well as the P-leaf content and grain yields of wheat and soybean crops. The results showed that the P content in the soil surface decreased over time in plots without P addition. The annual application of phosphate fertilizers at 100 kg P2O5 ha-1

in the wheat crop, regardless of the mode and source of application, was sufficient to maintain a high level of P in the soil after 5 years, similar to the initial level. This resulted in high P-leaf content and high grain yields in a wheat-soybean crops sequence.

Furthermore, the results indicated that the application of phosphate fertilizers in the sowing furrow or by broadcast in wheat, using MAP or SSP as sources, is a strategy that should be encouraged to minimize P fixation on soil particles, improve P-leaf content, and increase wheat and soybean grain yields in highly weathered soils under no-till systems. In chapter 4, the focus was on analyzing the efficiency of various S sources (SSP, PG, and ES) in increasing wheat and soybean grain yields and maintaining an adequate level of S in the soil. The results showed that the SO4-S content in the soil profile increased with the applied S sources (SSP, PG, and ES). Additionally, the S-leaf content of wheat increased with ES and PG applications, and the S-leaf content of soybean increased with PG application. Although a trend was observed for S sources to increase cumulative wheat grain yield by 2% to 13%, there was no significant influence of the application of S-fertilizers on wheat and soybean grain yields. The results also indicated that a soil SO4-S level of 13 mg dm-3

in the 0–0.20 m depth was sufficient to supply the demand for S by a wheat-soybean succession under no-till. Overall, the chapters highlight the importance of proper management practices, such as surface liming, and P and S fertilization in improving soil fertility, crop nutrition, and grain yields under a no-till farming in Southern Brazil. The findings have important implications for the success of sustainable agriculture for food production in Brazil and other regions with similar climatic and soil conditions.