Yield increases by fertilizer application impose higher crop water use, as biomass production is positively correlated with transpiration. To quantify effects of N fertilizer supply on evapotranspiration (ET) of winter wheat, a field experiment with three nitrogen rates (N0, N120 and N230) under non‐water‐limited conditions was performed during 2014 and 2015. Normalized difference vegetation index (NDVI) was used to derive crop coefficients which were used to calculate N effects on bare soil evaporation (E), transpiration, evapotranspiration (ET), grain yield and harvest index (HI). E during the early post‐winter growth period was measured with micro‐lysimeters and compared with model estimates. N fertilizer supply resulted in lower cumulative E, and increases in grain yield were higher than increases in ET, resulting in a higher agronomic water‐use efficiency (WUE_Y). HI of treatment N120 was higher than that of treatment N230 indicating that HI was not the main reason of higher WUE_Y of treatment N230. It is concluded that estimates of ET under variable N supply require consideration of N‐induced effects on canopy development which could be successfully monitored by NDVI measurements. N supply increases ET and WUE_Y potentially imposing a trade‐off between water conservation and efficiency of water use for crop production.

中文翻译：

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基于NDVI的冬小麦蒸发蒸腾量估算值表明，施用氮肥对农用水分利用率有积极影响

施肥增加了产量，增加了作物用水量，因为生物量的产生与蒸腾量成正相关。为了量化氮肥供应对冬小麦蒸发蒸腾（ET）的影响，在2014年和2015年进行了在非水限制条件下以三个氮含量（N0，N120和N230）进行的田间试验。归一化植被指数（NDVI） ）被用来得出作物系数，这些系数被用来计算N对裸土蒸发量（E），蒸腾作用，蒸散量（ET），谷物产量和收获指数（HI）的影响。冬季后早期的E用微型测微计测量，并与模型估计值进行比较。氮肥供应导致较低的累积E，而谷物产量的增加高于ET的增加，_Y）。N120处理的HI高于N230处理，表明HI不是N230处理的WUE _Y较高的主要原因。结论是，在可变氮供应下的ET估算需要考虑N对冠层发育的影响，这可以通过NDVI测量成功监测。氮供应增加了ET和WUE _Y，可能在节水和作物生产用水效率之间进行权衡。