Gonçalves Ivo Z, Neale Christopher M U, Suyker Andy, Marin Fábio R
Daugherty Water for Food Global Institute, University of Nebraska, Lincoln, NE, USA.
Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE, USA.
Int J Biometeorol. 2023 Nov;67(11):1869-1879. doi: 10.1007/s00484-023-02547-8. Epub 2023 Sep 6.
Irrigation water requirements are commonly estimated based on the estimated crop evapotranspiration (ET) as determined by the reference evapotranspiration (ETr) and crop coefficient (K). Recent studies show that, at high evaporative demand (high ETr), K tends to decrease, creating an inverse ETr-K relationship. The focus of this long-term study is to, if at high atmosphere demand, there is the same inverse ETr-K relationship in Nebraska, USA, one of the most intensely irrigated regions in the world, and as a result, propose an adjustment to the Kc-ETr approach. The study was carried out in eastern Nebraska for maize-soybean rotation fields for the period 2002-2012. The Kc was estimated based on energy balance data from eddy covariance flux towers installed in the field and a nearby automated weather station throughout the growing seasons. We found that average Kc values varied depending on the year under high ETr; measured ETc agreed reasonably well with the FAO-56 manual predicted values, but in years with high ETr such as 2012 and 2002 affecting ETc values over the growing season. It was observed that Kc decreased as ETr increased, mainly when ETr reaches values greater than 6 mm d (P values < 0.001). This most likely was due to internal plant stomatal resistance to vapor release from the leaves diffusing to the atmosphere at high atmospheric demands. So, the time-based Kc curves described by FAO 56 manual should be adjusted for the analyzed crops considering different ranges of ETr to improve the required irrigation depth and irrigation management.
灌溉需水量通常根据参考作物蒸散量（ETr）和作物系数（K）确定的作物蒸散量（ET）估算得出。最近的研究表明，在蒸发需求较高（ETr较高）时，K往往会降低，从而形成ETr - K的反比关系。这项长期研究的重点是，在美国内布拉斯加州（世界上灌溉最密集的地区之一），在高大气需求情况下是否存在相同的ETr - K反比关系，并据此对Kc - ETr方法提出调整建议。该研究于2002年至2012年期间在内布拉斯加州东部的玉米 - 大豆轮作田进行。Kc是根据整个生长季节安装在田间和附近自动气象站的涡度相关通量塔的能量平衡数据估算得出的。我们发现，在高ETr情况下，平均Kc值因年份而异；实测的ETc与粮农组织 - 56手册预测值相当吻合，但在2012年和2002年等ETr较高的年份，其影响了整个生长季节的ETc值。观察到随着ETr增加，Kc降低，主要是当ETr达到大于6毫米/天的值时（P值<0.001）。这很可能是由于在高大气需求下，植物内部气孔对叶片向大气扩散释放水汽存在阻力。因此，对于所分析的作物，应根据不同的ETr范围对粮农组织56手册描述的基于时间的Kc曲线进行调整，以改善所需的灌溉深度和灌溉管理。
