Effects of water stress on evapotranspiration of soybean

Міжвідомчий тематичний науковий збірник "Меліорація і водне господарство" Pub Date : 2021-05-07 DOI:10.31073/mivg202101-266

O. Zhuravlov, A. Shatkovskyi, V. Vasiuta

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Abstract

Based on the results of observations, it was specified that when decreasing soil moisture there is a disproportionate decrease in the average daily evapotranspiration (ET). Thus, in the range of soil moisture of 94-80% minimum moisture-holding capacity (MMHC) ET was 9,76 mm a day, and in the range of 70-62% MMHC - its value decreased by 3 times. When the soil moisture reached 58,5% MMHC, the value of ET did not exceed 0,5 mm a day, which is 20 times less than the initial one. It was determined that the decrease in soil moisture by 10% in the range of 90 - 70% MMHC occurs during 3 days, and from 70 to 60% MMHC and from 60 to 58% MMHC - during 8 days. When soil moisture is 70% MMHC and below, the actual evapotranspiration is less than ETo that proves the effect of water stress on soybeans ET. When calculating water stress coefficient (Ks), a mathematical model based on the dependence of Ks on soil moisture as a percentage of MMHC was obtained. The average absolute percentage error (MAPE) is 8,6%, which corresponds to the high accuracy of the obtained dependence. In the range of soil moisture from 58 to 80% MMHC, the water stress coefficient is calculated by the formula Ks =-0.0011·FC²+0.1925·FC-7,4541. When having soil moisture as 80% MMHC and above, Ks = 1. A comprehensive comparative assessment of existing methods for calculating waster stress coefficient Ks was taken and it was found out that the actual values of Ks when having soil moisture as 80-70 and 60-65% MMHC by 8-14 % and 72-32 %, respectively, less than Ks FAO 56, and by 35-40 % larger than those determined by Saxton method. It was proved the need of taking into account the reduction in evapotranspiration when calculating water balance under water stress of plants. The calculation of evapotranspiration (ETs) by the Penman-Monteith method, without taking into account the water stress coefficient, showed that the value of the actual and calculated water balance coincides only when soil moisture does not exceed 62% MMHC. With a further decrease in soil moisture, the estimated soil moisture was 20% less than the actual, which led to the errors in determining soil moisture after irrigation, because its actual value was almost 100% MMHC, and the estimated one was only 60% MMHC. It was proved that the determination of water balance by calculation methods without taking into account the water stress coefficient leads to significant errors.

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水分胁迫对大豆蒸散的影响

根据观测结果，明确了当土壤水分减少时，平均日蒸散量(ET)会不成比例地减少。因此，在土壤湿度为94 ~ 80%的范围内，最小持湿量ET为9.76 mm / d，在土壤湿度为70 ~ 62%的范围内，其值减少了3倍。当土壤湿度达到58.5% MMHC时，ET值不超过0.5 mm / d，比初始值减少了20倍。结果表明，在90 ~ 70% MMHC范围内，土壤湿度在3 d内下降10%，在70 ~ 60%和60 ~ 58% MMHC范围内下降8 d。当土壤湿度为70% MMHC及以下时，实际蒸散量小于ETo，证明水分胁迫对大豆蒸散量的影响。在计算水分胁迫系数(Ks)时，得到了基于Ks与土壤湿度占MMHC百分比关系的数学模型。平均绝对百分比误差(MAPE)为8.6%，对应于获得的相关性具有较高的准确性。在土壤湿度为58 ~ 80% MMHC范围内，水分胁迫系数的计算公式为Ks =-0.0011·FC²+0.1925·FC-7,4541。当土壤含水量为80%及以上时，Ks = 1。对现有的土壤应力系数计算方法进行了综合比较评价，发现土壤含水量为80-70和60-65% MMHC时的实际值分别比kfao 56小8- 14%和72- 32%，比Saxton法计算的结果大35- 40%。结果表明，在计算植物水分平衡时，需要考虑植物蒸散量的减少。在不考虑水分胁迫系数的情况下，Penman-Monteith法计算蒸散发(ETs)的结果表明，只有当土壤湿度不超过62% MMHC时，实际水量平衡值与计算水量平衡值才吻合。随着土壤湿度的进一步降低，土壤湿度估计值比实际值低20%，导致灌溉后土壤湿度的测定存在误差，因为其实际值几乎为100% MMHC，而估计值仅为60% MMHC。结果表明，采用不考虑水分胁迫系数的计算方法确定水量平衡存在较大误差。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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Міжвідомчий тематичний науковий збірник "Меліорація і водне господарство"

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