Alvadi Antonio Balbinot Junior

Soil structure can mitigate both mechanical impedance and water stress, thereby modulating root elongation and access to deep soil water. Although process-based root growth models represent soil–root interactions, they rarely account explicitly for structural conditions and their consequences for the combined effects of water and mechanical stresses on root growth. We quantify how soil structure under no-tillage influences soybean root elongation, effective rooting depth, and water-deficit mitigation, and we parameterize these effects in a biophysical root-growth model. A long-term field experiment established in 2016 compared three cropping systems preceding soybean (Glycine max): ruzigrass (Urochloa ruziziensis), maize (Zea mays), and fallow. Soybean root length density and soil physical attributes were measured in nine layers down to 210 cm. Effective rooting depth was defined as the depth containing 95% of total root length. Plant-available water was computed from soil water retention between −60 and −15,000 hPa, and readily available water was assumed as 50% of plant-available water within the rooted zone. Grain yield was determined at harvest. In addition, soybean root elongation rate was measured in the laboratory using core from field and repacked samples across gradients of degree of saturation and soil penetration resistance. The structural effect was incorporated as a parameter in a biophysical model that combines water and mechanical limitations to root elongation. Increasing soil penetration resistance from 1.0 to 3.5 MPa reduced relative root elongation by 46% in preserved structure, whereas reductions reached 76% in repacked soil. At 0.5 MPa and 60% degree of saturation, elongation in repacked soil was 29% higher than in preserved structure, but both structural conditions converged as soil penetration resistance increased to 1.0 MPa. Under 90% degree of saturation, elongation in preserved structure was nearly threefold that in repacked soil. In the field, effective soybean rooting depth (in a trench of 210 cm depth) differed among previous cropping systems, with ruzigrass promoting substantially deeper roots (154.7 cm at 95% cumulative distribution) compared with maize (127.9 cm) and fallow (121.0 cm). Root length density in the 0 to 10 cm layer was highest after ruzigrass (4.72 cm cm-3), followed by maize (3.33 cm cm-3) and fallow (2.48 cm cm-3). Cumulative root length in the soil profile from 0 to 210 cm reached 202.2 cm cm-2 after ruzigrass, compared with 128.4 cm cm-2 after maize and 94.3 cm cm-2 after fallow. Soybean yield was 2.9 (after ruzigrass), 2.6 (after maize), and 2.1 Mg ha-1 (after fallow). Plant-available water in the soybean root zone was 175 mm after ruzigrass, compared with 145 mm after maize and 140 mm after fallow, indicating a 25% increase relative to fallow. Assuming evapotranspiration of 7 mm d-1, this represents approximately 15 days of water supply after ruzigrass versus 12 days after fallow. Preserved soil structure improved soybean root performance under strong physical constraints and increased deep water access. Explicitly representing soil structural conditions in simulation models can improve predictions of rooting depth and drought mitigation under no-tillage.Acknowledgements: AGRISUS Foundation [PA 3534/23], CNPq [409621/2023-4] and FAPESP [23/10427-3 and 23/11945-8].

Continuous use of the traditional soybean-maize off-season double cropping system in warm areas of southern Brazil has a negative effect on agricultural land owing to reduced straw cover on the soil, soil compaction under no-tillage and weed infestation. The aim of the work was to evaluate crop yield and profitability of alternative cropping systems to the soybean-maize off-season in southern Brazil. The experimental design consisted of randomized blocks with four replications, and involved eight cropping systems with various levels of diversification and intensification. Considering all three cultivation cycles, the average soybean yield was 12% higher in soybean-maize off-season intercropped with ruzigrass in comparison with the traditional soybean-maize off-season system. Moreover, compared with the traditional system, the yield of off-season maize increased by 4.4 and 8.2%, respectively, following the introduction of wheat or oat as a third crop between maize harvesting and soybean sowing. The profitabilities of soybean-maize off-season intercropped with ruzigrass and soybean-maize off-season with a third crop of oat or wheat were, respectively, 11.3, 10.2 and 6.6% higher than that of the traditional system. Under the conditions of the study, we identified three diversified crop rotation systems that present agronomic and economic advantages over the soybean-maize off-season double cropping system: soybean-maize off-season intercropped with ruzigrass; soybean-maize off-season with wheat as a third crop; and soybean-maize off-season with oats as a third crop.

Corn cultivated as a second-season crop (“safrinha”) is often subjected to water-deficit conditions, which exacerbate the negative effects of soil compaction, reduce nitrogen fertilization efficiency, and consequently decrease grain yield. The objective of this study was to evaluate the effects of subsoiling and topdressing nitrogen fertilization on the performance of second-season corn under water deficit. The experiment was carried out in Londrina, Paraná State, Brazil, during the 2023 and 2024 growing seasons, in a randomized complete block design with split plots. In the main plots, two levels of nitrogen topdressing were tested: absence of N and application of 80kgha⁻¹ of N. In the subplots, the presence or absence of subsoiling was evaluated. Two years after subsoiling, a reduction in soil penetration resistance was observed, mainly in the 0.15–0.30m layer, due to soil loosening. In both growing seasons, severe water deficit occurred during the crop cycle. No effect of nitrogen topdressing on grain yield was detected. In the 2023 season, the treatment without subsoiling showed a higher corn yield (6.2t ha⁻¹) compared to subsoiled plots (5.4tha⁻¹). In the 2024 season, subsoiling did not affect grain yield.

The objective of this work was to evaluate the effects of soil management on soybean grain yield and grain protein and oil concentrations, in long-term experiments. Data from three long-term experiments conducted in Londrina, in the state of Paraná, Brazil, were analyzed in two growing seasons with different water availabilities. Grain yield was higher in the no-tillage system (NTS) compared with treatments with soil mobilization (3,972 kg ha-1 vs 3,421 kg ha-1 in the 2022/2023 season and 2,468 kg ha-1 vs 2,043 kg ha-1 in the 2023/2024). Grain protein concentration was also higher in treatments under NTS compared to treatments with soil mobilization (382 g kg-1 vs 370 g kg-1 in the 2022/2023 season and 382 g kg-1 vs 371 g kg-1 in the 2023/2024). Grain oil concentration was lower in the treatments under NTS , when compared with those with soil mobilization (217 g kg-1 vs 222 g kg-1 in the 2022/2023 season and 215 g kg-1 vs 222 g kg-1 in the 2023/2024). NTS reconciles a greater soybean grain yield with a higher grain protein concentration.

Devido ao recente aumento no custo do germoplasma, royalties de biotecnologia e tratamentos de sementes, estudos vêm sendo realizados para analisar a capacidade das cultivares modernas de soja, de manter o rendimento de grãos sob densidades de semeadura (DS) reduzidas. Este estudo objetivou elucidar o efeito da redução da DS no índice de área foliar (IAF) e na interceptação de luz pelo dossel de cultivares de soja com potencial de ramificação contrastantes e identificou a associação dessas variáveis com o rendimento de grãos. Os experimentos de campo foram conduzidos em blocos casualizados, utilizando-se as cultivares BRS 1010IPRO (alta plasticidade) e NS 5959IPRO (média plasticidade), com cinco DS: 100, 80, 60, 40 e 20% da DS recomendada. A redução da DS não reduziu o rendimento de grãos até o ponto em que o IAF e a interceptação luminosa na fase reprodutiva foram semelhantes aos obtidos com a DS recomendada. Maior IAF e interceptação luminosa em cultivares com maior plasticidade de ramificação conferem maior potencial de redução da DS. A densidade de semeadura mínima ótima (DSMO) para IAF, Índice de Vegetação por Diferença Normalizada (NDVI) e radiação fotossinteticamente ativa interceptada (RFAI) acumulados, na fase reprodutiva foi mais próximo da DSMO para produção de grãos do que na fase vegetativa ou no ciclo total da cultura, indicando “crescimento de luxo” na fase vegetativa nas DS recomendadas. O IAF, o NDVI e a RFAI acumulados na fase reprodutiva tiveram maior correlação com o rendimento de grãos do que aqueles na fase vegetativa ou no ciclo total. O NDVI acumulado apresentou maior correlação com o rendimento de grãos do que o IAF e a RFAI acumulados.

Soybean [Glycine max (L.) Merr.] yield and profitability can be affected by plant‐to‐plant spatial uniformity and sowing rate. This study aimed to evaluate the agronomic and economic performance of soybean in relation to the spatial distribution of seeds in rows and seeding rates. A field experiment was conducted during the 2018–2019 and 2019–2020 growing seasons in Londrina, Paraná state, Brazil. We evaluated three coefficients of variation of seed distribution in rows (coefficient of variation of seeds distribution (VDS): 0%, 50%, and 100%) and four seeding rates (350,000, 262,500, 175,000, and 87,500 seeds ha⁻¹), which corresponded to 100%, 75%, 50%, and 25% of the recommended seeding rate of the cultivar BRS 1003 IPRO, respectively. Sowing was performed manually to ensure that seed distribution accurately adhered to the experimental setup. Soybean yield components, yield, and profitability were then evaluated. The lower VDS improved the yield by 374 kg ha⁻¹ compared to the higher VDS and increased the profitability by $334.7 ha⁻¹ in 2019–2020. A seeding rate of 262,500 seeds ha⁻¹ yielded the highest grain yield. The highest soybean profitability was achieved at a seeding rate 6.5% lower than that which produced the highest yield. Branching is essential in compensating for lower seeding rates and plants with uneven spatial distributions. The present study shows that equidistant distribution of seeds in rows optimizes grain yield.

A redução da densidade de semeadura tem sido estudada como uma estratégia para redução do custo de produção de soja, sem alterações na produtividade. Entretanto esta técnica pode impactar diretamente na produção e formação das sementes, pois altera a morfologia da planta e modifica a competição intraespecífica, a eficiência do uso da água e o microclima. O objetivo foi investigar se o cultivo de soja em densidades reduzidas, altera o potencial fisiológico das sementes, em diferentes posições da planta, em duas cultivares com potencial de ramificação discrepante. O delineamento foi inteiramente casualizado, com parcelas subdivididas considerando-se: cinco densidades de semeadura (100, 80, 60, 40 e 20% da densidade recomendada pelo obtentor), na parcela e três posições de sementes na planta (inferior, médio e superior), na subparcela. Utilizou-se as cultivares BRS 1010 IPRO e NS 5959 IPRO. Avaliou-se a germinação, primeira contagem da germinação, comprimento e massa seca de plântulas, condutividade elétrica, envelhecimento acelerado e emergência em areia. O potencial fisiológico das sementes é maior no estrato superior da planta em comparação com o inferior. A redução da densidade de semeadura para valores até 40% da densidade não provoca impactos significativos sobre o potencial fisiológico das sementes. A redução drástica da densidade de semeadura, para apenas 20% do recomendado, resulta em menor vigor de sementes. A germinação das sementes das cultivares NS 5959 IPRO e BRS 1010 IPRO é maior em densidades de semeadura variando entre 40 e 80% do recomendado pelos obtentores.