Quantifying the compensatory effect of increased soil temperature under plastic film mulching on crop growing degree days in a wheatmaize rotation system

Plastic film mulching (PM) has a compensatory effect on crop growing degree days by increasing soil temperature. However, only few studies addressed the question whether a terminal time for the compensatory effect window exists and if it exists how it can be quantified. The objective of this study was to use the logistic equation to describe the cumulative crop plant height and to quantify the compensatory effect. Crop apical meristem emergence was used as the reference for the terminal time of the compensatory effect window. A three-year field experiment (2013-2016), conducted under continuous PM in a typical winter wheat (Triticum aestivum L.) and summer maize (Zea mays L.) rotation on the Loess Plateau, Northwest China, indicated that the logistic equation performed well in representing and quantifying the compensatory effect of PM. The compensatory effect of PM reached a plateau during winter wheat growing seasons due to the lack of increased soil temperature during regreening stage, and during summer maize growing seasons due to unfavorably delayed senescence. The terminal time can be estimated during winter wheat and summer maize growing seasons from thermal time nodes at the maximum slope (t2) and second inflection point (t3), respectively. The compensatory coefficients could be estimated by thermal time intervals of (0, t1) and (t1, t2) in winter wheat growing seasons and thermal time internals (0, t1), (t1, t2), and (t2, t3) in summer maize growing seasons, respectively. Compensatory coefficients tended to increase with maize plant development. The minimum data requirement using a logistic equation to calculate compensatory coefficients includes data for staged plant height and mean daily air temperature.