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

Mateus Possebon Bortoluzzi,Roberto Trentin,Astor Henrique Nied,Paulo Ivonir Gubiani,Arno Bernardo Heldwein,Jocélia Rosa Da Silva,Alencar Junior Zanon

doi:10.4136/ambi-agua.2614

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.

Highlights

High demand for vegetable protein and favorable economic condition enables the expansion of soybean cultivation in areas that were not traditionally cultivated, i.e., the lowland areas in southern Brazil (Rocha et al, 2017; Sartori et al, 2016), entailing 1/3 of the area traditionally sown with irrigated rice (IRGA, 2019)
The sequential water balance (SWB) modeling strategy that estimated the number of excess water (EXC) days closest to the number of EXC days observed in the field (38 days) was MACPM, with 35 days of EXC (Table 1)
The strategies that used effective precipitation (EP) calculated by the U.S Soil Conservation Service methodology as an estimate of soil water infiltration underestimated the number of days with EXC

Summary

Introduction

High demand for vegetable protein and favorable economic condition enables the expansion of soybean cultivation in areas that were not traditionally cultivated, i.e., the lowland areas in southern Brazil (Rocha et al, 2017; Sartori et al, 2016), entailing 1/3 of the area traditionally sown with irrigated rice (IRGA, 2019). In areas cultivated with irrigated rice, the superficial layers undergo disruption and compaction due to mechanized operations used for rice cultivation, which usually take place under soaked soil conditions and reduce the water infiltration rate (Sartori et al, 2016). Excess water is one of the main risk factors for soybean grown in lowland areas (Bortoluzzi et al, 2017; Gubiani et al, 2018). Prediction of risks due to excess water requires modeling the water balance throughout the crop cycle. Bortoluzzi et al (2017) carried out a risk analysis of excess water for soybean cultivation in lowlands in the central region of Rio Grande do Sul (RS) by adapting the calculation of the daily sequential water balance (SWB) of Thornthwaite and Mather (1955). Another assumption was that after soil saturation two days of drainage were required for water content to decrease to field capacity

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Conclusion