Water balance for determination of excess water in soybean cultivated in lowland soils

Abstract

The aim of this study was to derive a methodology for calculating a sequential water balance that accurately estimates the occurrence of excess water in soybeans cultivated in lowlands. We tested four calculation strategies of water balance associated with the simulation of soybean development, which differed on the calculation of rainfall and time of water drainage from the soil macropores. Data of volumetric moisture monitored in three soil layers throughout the soybean cycle in the 2014/15 agricultural year were used as a reference. Microporosity was used as a lower limit for the occurrence of excess water in the area. Excess water was considered to be whenever the daily volumetric soil moisture in the 0-100 mm layer was greater than 0.39 mm3 mm-3. Over the 111 days of measurement, soil moisture indicated the presence of excess water in 38 days. The traditional calculation strategy of water balance underestimated the occurrence of excess water, as well as the other strategies that considered effective precipitation in their formulas. The calculation strategy that considers that all the rainfall infiltrates in the soil and that the water from macropores is removed only by crop evapotranspiration exhibited good performance and indicated 35 days of excess water, being the most appropriate and recommended for determining excess water in lowland soybeans.

Tolerance of soybean cultivars to flooding stress in vegetative growth stages

“…Therefore, in lowlands, soybean producers must invest in drainage systems to reduce the risks associated with excess soil water, especially at the VE-V4 initial stages, considered the most susceptible. Although all plants survived after emergence in the present study, under field conditions, the cracking of the epidermis due to aerenchyma formation contributes to soil-fungi infection, which is responsible for plant death in the crop rotation system with soybean and flooded irrigated rice (Irga, 2018;Goulart et al, 2020;Bortoluzzi et al, 2021a). From the V4 stage onwards, even though soybean showed a higher tolerance to flooding stress, significant losses in yield potential were caused by the anaerobic environment, which induced the plant to adopt a metabolism with a lower energy gain (Taiz et al, 2017).…”

“…Therefore, to apply the results obtained in the rice-soybean rotation system, farmers must take into account meteorological broadcasts and the possibility of soil flooding, avoiding sowing during periods of excess rain because, regardless of the crop year, there will be problems related to soybean germination and emergence in anaerobic environments (Bortoluzzi et al, 2021a).…”