Baral Rudra, Lollato Romulo P, Bhandari Kamal, Min Doohong
Department of Agronomy, Kansas State University, Manhattan, KS, United States.
Department of Physics, Kansas State University, Manhattan, KS, United States.
Front Plant Sci. 2022 Jul 27;13:931403. doi: 10.3389/fpls.2022.931403. eCollection 2022.
The United States (US) is the largest alfalfa ( L.) producer in the world. More than 44% of the US alfalfa is produced under rainfed conditions, although it requires a relatively high amount of water compared to major field crops. Considering that yield and production of rainfed alfalfa have been relatively stagnant in the country for decades, there is a need to better understand the magnitude of yield loss due to water limitation and how far from yield potential current yields are. In this context, the main objective of this study was to estimate the current yield gap of rainfed alfalfa in the US. We collected 10 year (2009-2018) county-level government-reported yield and weather data from 393 counties within 12 major US rainfed alfalfa producing states and delineated alfalfa growing season using probabilistic approaches based on temperature thresholds for crop development. We then calculated county-level growing season rainfall (GSR), which was plotted against county-level yield to determine attainable yield (Ya) using frontier function analysis, and water-limited potential yield (Yw) using boundary function analysis. Average and potential water use efficiencies (WUE) were estimated, and associated yield gap referring to attainable (YGa) or water-limited yields (YGw) were calculated. Finally, we used conditional inference trees (CIT) to identify major weather-related yield-limiting factors to alfalfa forage yield. The frontier model predicted a mean Ya of 9.6 ± 1.5 Mg ha and an associated optimum GSR of 670 mm, resulting in a mean YGa of 34%. The boundary function suggested a mean Yw of 15.3 ± 3 Mg ha at the mean GSR of 672 ± 153 mm, resulting in a mean yield gap of 58%. The potential alfalfa WUE was 30 kg ha mm with associated minimum water losses of 24% of mean GSR, which was three times greater than the mean WUE of 10 kg ha mm. The CIT suggested that GSR and minimum temperature in the season were the main yield-limiting weather variables in rainfed alfalfa production in the US. Our study also revealed that alfalfa was only limited by water availability in 21% of the environments. Thus, future research on management practices to narrow yield gaps at current levels of water supply is necessary.
美国是世界上最大的苜蓿生产国。美国超过44%的苜蓿是在雨养条件下生产的，尽管与主要大田作物相比，苜蓿需要相对较多的水分。鉴于几十年来美国雨养苜蓿的产量和产量一直相对停滞不前，有必要更好地了解水分限制造成的产量损失程度以及当前产量与产量潜力的差距有多大。在此背景下，本研究的主要目的是估算美国雨养苜蓿目前的产量差距。我们收集了美国12个主要雨养苜蓿生产州内393个县的10年（2009 - 2018年）县级政府报告的产量和天气数据，并使用基于作物发育温度阈值的概率方法划定苜蓿生长季。然后，我们计算了县级生长季降雨量（GSR），将其与县级产量作图，使用前沿函数分析确定可实现产量（Ya），并使用边界函数分析确定水分限制潜在产量（Yw）。估算了平均和潜在水分利用效率（WUE），并计算了与可实现产量（YGa）或水分限制产量（YGw）相关的产量差距。最后，我们使用条件推断树（CIT）来识别与天气相关的苜蓿饲草产量主要限制因素。前沿模型预测平均Ya为9.6±1.5 Mg ha，相关的最佳GSR为670毫米，平均YGa为34%。边界函数表明，在平均GSR为672±153毫米时，平均Yw为15.3±3 Mg ha，平均产量差距为58%。苜蓿潜在WUE为30 kg ha mm，相关的最小水分损失为平均GSR的24%，这是平均WUE 10 kg ha mm的三倍。CIT表明，GSR和该季节的最低温度是美国雨养苜蓿生产中主要的产量限制天气变量。我们的研究还表明，在21%的环境中苜蓿仅受水分供应的限制。因此，有必要开展关于管理措施的未来研究，以在当前供水水平下缩小产量差距。
