Shift in agricultural phenophases and its implications for soil erosion in the Loess Plateau of China

Background/Question/Methods Loess soils are found on some of the most productive and widespread agricultural lands around the world, but the sustainability of these areas are increasingly threatened by soil erosion.  In the Loess Plateau of China, the conventional agricultural practice – winter wheat cropping – leaves the field in fallow for the summer when heavy rainstorms usually occur.  This has led to accelerated soil erosion that undermines the sustainability of the Loess Plateau (Wang et al., 2010). The longer the fallow period, the higher the erosion risks.  Previous studies in the region have focused mainly on vegetation responses to climate change, and little is known about how changes in the phenophases of agricultural plants are related to soil erosion risks. In this study, we examine the phonological records of crops (for more than 20 years) across the Loess Plateau to examine how the climate has influenced the timing and duration of different phonological events.  Trends are derived from linear regression, and the Mann-Kendall test is used for the test of statistical significance at the 95% confidence level.

Results/Conclusions During the period of 1981-2005, more than 85% of the sample sites showed a significant increasing trend in spring temperature over the Loess Plateau at the significant level of 0.05.  The rising temperature caused a significant shift in the timing of winter wheat.  Consequently, the sowing date of winter wheat was delayed by 4 days/decade (P<0.01) for the period of 1981-2005, while flowering and maturity dates became earlier by 5.0 and 5.6 days/decade (P<0.01), respectively.  The fallow period (from sowing to harvesting) was lengthened by 8.7 days/decade (P<0.01).  The number of fallow days was significantly correlated with spring temperature.  These changes in the phenophases of cropfields resulted in an increasingly longer summer fallow period, which may have been a major cause for the accelerated soil erosion in the region during the past several decades.