Benefits of direct planting in the development of soybean crops

The Direct Planting System (SPD) is based on the concept that, with the addition of residues from cover crops, it is possible to contribute more carbon to the system, greater vegetation coverage and minimal soil mobilization, providing and maintaining the physical quality of the soil and consequently a greater benefit to the environmental revitalization of a given agroecosystem. With the development of the direct seeding system, mobilization restricted to the seeding line and the conservation of the surface covered by previous crop residues reduce the action of erosion. Soil erosion is a process that also accounts for the reduction in soil organic matter levels. The loss of soil and nutrients through water erosion is a determining factor in soil impoverishment and reduced productivity of most crops (Alves, et al.

In view of conservation management practices, crop rotation provides physical, chemical and biological benefits for the soil and improves the productivity of large crops, favoring net gains for the producer and sustainability. Grass treatments favor increased soil aggregation, reduced density, increased porosity and increased humification according to the N dose.

This work was installed in Capão Bonito, in the experimental area located at the Agronomic Institute of Campinas IAC/Apta/SAA. The average altitude is 600 meters, the slope is 6,5% and the relief is gently undulating. The soil is classified as a dystrophic Red Oxisol and the climate is subtropical (type Cfa). The experimental design used was randomized blocks, comprising five treatments and four replications. Each plot measures 200m² in area (20m long and 10m wide). The cover crops for autumn-winter and spring were: white oat (IAC-7) and lupine (The white wolf). Soybean productivity was evaluated in the direct seeding cultivation system, as well as the application of nitrogen in cover crops in autumn/winter cover crops with five treatments. During the autumn/winter period, the cover crops received 30kg/ha of N (T2) and 60kg/ha of N (T3). Another treatment without N (T1), legumes (T4), and fallow (T5) was evaluated as a control.

At the end of October, the cover crops were dried for planting the summer crop, that is, transgenic soybeans using Round UP Ready 7908 (RR) technology adapted to the Campinas region. After harvest, plant height and productivity of the soybean crop were measured. In the experimental plots, mini-trenches were opened to collect composite soil samples from the stratified surface layers 0m – 0,025m, 0,025m – 0,05m, 0,05m – 0,10m and 0,10m – 0,20m, being six subsamples to form a composite sample. After collection, the samples were air-dried and sieved through a 2mm mesh sieve to obtain the air-dried fine earth fraction (TFSA).

For detailed studies of lability and humification of soil organic matter, samples were prepared through physical fractionation by granulometry using the Sonifier-Branson ultrasound (Feller et al, 1947), to disperse soil fractions into different particle sizes such as sand (>53 microns). After sonication, the sample was removed and its contents were sent to a 53 micron sieve, where the sample was washed with distilled water and the particle with labile carbon linked to the sand fraction obtained. This fraction was subjected to oven drying at 45 degrees Celsius in 400ml beakers. After drying, the sand samples were ground in a mortar and sieved through a 100 mesh sieve, one gram of the sand fraction that passed through the sieve was stored in tubes of eppendorf for reading the CNHS. The remainder of the sample (clay and silt particles) was taken to 2.000ml beakers for fractionation by sedimentation.

The tubes eppendorfs containing soil fractions were analyzed in the Fertility Sector, belonging to the IAC Soil Center. To read the C (carbon), N (nitrogen) and S (sulfur) of the samples, they were weighed with approximately 100mg of the fraction and mixed with the same amount of tungsten oxide substance. This mixture was compartmentalized into tablets where they were sent for reading on a CNHS elemental analyzer, Elementar brand, model Vario Macro. Since the characterization of the experimental area, there has been an increase in soil density values ​​in Campinas, even with the continued addition of residues. Due to higher temperatures in summer and dry winters, the adoption of cover crops may not be efficient in improving soil structure and reducing compaction, however, the increase in carbon content may contribute to the sustainability of the system. .

In Capão Bonito it is possible to allocate five plants in two agricultural years, contributing to the addition of phytomass in coverage and faster cycling within the agroecosystem, even with a good distribution of rainfall throughout the year. The greater the addition of N, the greater the contribution of the more humified fractions, initially, and this aspect can be reversed in the soil, depending on the rotation system adopted.

Conclusions

Particulate organic matter (> 53 microns) in Capão Bonito is always higher with the use of cover crops. However, in a subtropical climate, the supply of phytomass is facilitated depending on the climate.

Through the particle size fractions evaluated, greater or lesser humification can be inferred, depending on the C/N ratio, mainly for fractions 53 microns to verify the lability of the carbon.

This article was published in issue 184 of Cultivar Grandes Culturas magazine. Click here to read the edition.