Fig 1.
The semiarid area of northern China (the filled area) and the distribution of the thirty-eight meteorological stations including Wuchuan and Guyuan in the semiarid area of northern China.
Fig 2.
Temporal changes in average temperature (a, °C), minimum temperature (b, °C), maximum temperature (c, °C), precipitation (d, mm), Palmer Drought Severity Index (e), and the fertilization (f, kg ha-1) during 1980–2010 in semiarid area of northern China (SAC).
The inset in f illustrates differences of fertilizer in spring wheat, naked oat, potato and maize in Wuchuan (W) and Guyuan (G) in stage I and stage II. Columns labeled with the different letter are significantly different (P<0.05). P<0.01 represents the 1% level of significance; P<0.05 represents the 5% level of significance.
Table 1.
Changes in temperature, precipitation, and fertilizer application crop growth period during 1980–2010.
Fig 3.
Changes of WUEs of spring wheat (W, black), naked oat (N, red), potato (P, blue), and maize (M, yellow) in Wuchuan and Guyuan from 1983 to 2010, respectively.
P<0.01 represents the 1% level of significance; P<0.05 represents the 5% level of significance. A and B refer to the change trend of crop WUE from 1983–2010 at Wuchuan and Guyuan, respectively; C and D refer to the discrete level of WUE at Wuchuan and Guyuan, respectively. In the Fig C and D, “Minimum value”, “1/4 percentile value”, “Median (spot)”, “3/4 percentile value”, “Maximum value” are presented from bottom to top, which is the same case throughout this study. Numbers above box plots are coefficient of variation (CV) of WUE of different crop during the 1980s, the 1990s and the 2000s. I means the period of 1983–1999; II means the period of 2000–2010.
Fig 4.
Crop resilience of spring wheat, naked oat, potato, and maize in warm-wet environment (black dot) and warm-dry environment (red dot).
A, C and E is spring wheat, naked oat and potato in Wuchuan, respectively. B, D and F is spring wheat, potato and maize in Guyuan, respectively. Minimum (WUEmin) and maximum (WUEmax) (slope of the Yield/ET) in the wetter and drier years, respectively, are based on all crops for multi-year study periods. The insets illustrate the differences in WUEmin and WUEmax with mean Tmax, Tmin, PDSI, and fertilizer for each study periods. Columns labeled with the different letter are significantly different (P<0.05).
Table 2.
Correlation coefficients of water use efficiency of spring wheat, naked oat, potato, and maize with weather factors and fertilizer in the semi-arid area of northern China during 1983–2010 periods.
Fig 5.
Relationship of crop WUE and Tmax, Tmin, precipitation, and fertilizer during 1983–2010 in the SAC.
A, C and E is the relationship of WUE and Tmax, precipitation and fertilizer in Wuchuan, respectively. B, D and Fis the relationship of WUE and Tmin, precipitation, and fertilizer in Guyuan, respectively. The insets illustrate the change of WUE with elevated temperature and fertilizer usage (within the threshold). P<0.01 represents the 1% level of significance; P<0.05 represents the 5% level of significance.
Fig 6.
Crop yield changes of spring wheat, naked oat, potato, and maize by two panel regression models (PRM) for 1°C increase in temperature (A) and 10% decrease in precipitation (B) during crop growing season in Wuchuan and Guyuan from 1983–2010.
Table 3.
Impact of the warming-drying trend (WDT) and the amount of fertilizer on water use efficiency in wetter and drier years in different periods in semiarid area of northern China (SAC).
Table 4.
The difference of water use efficiency (millet, rape, and potato) in rotation and continuous cropping during 2008–2010.
Fig 7.
A conceptual model of crop resilience.
WUEmin represents the native WUE in the warm-wet environment (black solid line). WUEmax represents WUE affected by warm-dry environment with the same level of fertilization (dash line). WUEmin and WUEmax limited primarily by climate factors and agronomic measures with the arbitrary distinction made here at the most appropriate crop evapotranspiration for illustration only. A refers to crop wilting point of crop.