Abstract
ABSTRACT Irrigation management aimed at optimal production has been based only on the water factor. However, in addition to the water potential of the soil, factors such as soil penetration resistance and soil O2 diffusion rate also affect plant growth and interfere with water absorption, even if moisture is within the available water range. This study aimed at quantifying the least limiting water range and demonstrating its potential in soil and water management in irrigated agriculture. In order to determine the least limiting water range, soil water retention curves and soil resistance to penetration were determined from undisturbed soil samples. The sequential water balance and the reference, crop and real evapotranspiration were determined for a soybean crop season. Soil aeration was the least limiting water range upper limit for soils with bulk density greater than 1.33 Mg m-3, whereas soil resistance to penetration was the lower limit for bulk density higher than 1.43 Mg m-3. The bulk density of the soil studied was 1.35 Mg m-3, indicating 0.37 m3 m-3 of water availability, based on the least limiting water range, which is sufficient to supply the crop evapotranspiration. Irrigation management based on the least limiting water range is more efficient and complete than that based only on available water.
Highlights
Soybean requires water availability of 450-850 mm cycle-1 to keep yield (Embrapa 2003)
The soil water retention and soil resistance to penetration curve equations are shown in equations 8 and 9: θ = exp. (-0.92 - 0.06Bd ) ψ -0.04 R2 = 0.83 [8]
Estimated coefficients of the model of soil resistance to penetration indicate that Bd positively influenced the penetration resistance, being negatively influenced by the soil water content
Summary
Soybean requires water availability of 450-850 mm cycle-1 to keep yield (Embrapa 2003). The best soybean yield and development potential may be limited by water stress during critical development stages, especially at the germination-emergence and flowering-grain filling stages. The effect of stress due to water deficit and/or surplus is complex and depends on the cultivar, development stage and its duration (Maehler et al 2003, Fante et al 2010). Water surplus stress alters the root system cellular metabolism, inhibiting symbiotic fixation and absorption of nitrogen and other minerals, leading to root growth reduction and nodulation, probably due to the oxygen demand in the fixation process (Amarante & Sodek 2006). Water deficit reduces plant photosynthetic rate, mainly by inducing stomatal closure and reducing leaf expansion, which limits CO2 assimilation (Taiz & Zeiger 2009). Drought causes reduction of soybean growth rate and, lower grain yield (Almeida et al 2003)
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