JIA-2019-11

2477 ZHANG He et al. Journal of Integrative Agriculture 2019, 18(11): 2472–2482 45 60 75 90 105 0 0.5 1.0 1.5 2.0 2.5 EC 1:5 =0.03×SRWC–1.01×SRWC R 2 =0.54 ** n =360 df =358 EC 1:5 (dS m –1 ) SRWC (%) Fig. 4 Relationships between the conductivity with the 1:5 distilled water/soil dilution (EC 1:5 ) and soil relative moisture content (SRMC). ** , significant difference at P <0.01 probability level. with high salinity (groundwater depth at 0.6 m), standard soil moisture with high salinity (1.0 and 1.4 m), standard soil moisture with medium salinity (1.8 m), and slight drought with low salinity (2.2 and 2.6 m) (Table 3). 3.3. The combined effect of soil moisture and salinity on wheat growth and yield The LA values, SPAD readings, P n , the total aboveground biomass, grain yield, yield components, and flour quality (protein and starch content) at some of the growth stages were the maximal under the groundwater depths of 1.9 and 2.3 m in Y1, and under 1.8 and 2.2 m in Y2 were the minimal under the groundwater depth of 0.7 m in Y1, and under 0.6 m in Y2 (Tables 4 and 5, Figs. 5–7). It is clear from CV that the decrease in grain yield in 2013–2014 and 2014– 2015 were caused mainly by the reduction of productive spikes per pot, secondly the reduced 1 000-grain weight (Table 5). The groundwater depth and grain yield were highly correlated (Fig. 8), and the estimated optimal groundwater depth was 2.0 m in Y1 and 2.1 m in Y2. The regression equations indicated that the most sensitive stage of wheat response to the groundwater depth (combined soil moisture and salinity) was the booting stage for the LA values for the five stages, SPAD readings, and P n at jointing, booting, and filling stages in Y1 and Y2 (Table 6). 4. Discussion 4.1. Groundwater depth affecting soil moisture and salinity Our results showed that the SRMC for S2 were higher than that of S1, and the EC 1:5 for S2 were lower than that of S1 (Fig. 3). However, Malash et al . (2008) conducted an experiment on drip and furrow irrigation to tomato using salty water. They found that the soil moisture contents were higher in top 20 cm soil layer than that of root system (S2) after irrigation; the salt contents were lower at surface layer (0–15 cm) than that of 30 and 60 cm soil layers (Malash et al . 2008). The results of soil moisture and salinity in different layers were different from that of Malash et al . (2008). At the top soil layer, the saline water is provided with drip or furrow irrigation, and the salinity moves to deeper layers. From the seedling to the ripening period, the groundwater depth showed a negative relationship with SRMC and EC 1:5 Table 3 The means of five growth stages for soil relative moisture content (SRMC) and conductivity with the 1:5 distilled water/ soil dilution (EC 1:5 ) of 0–20 cm and 20–40 cm depths and their means 1) Groundwater depth (m) SRMC (%) EC 1:5 (dS m –1 ) 0–20 (cm) 20–40 (cm) Average (cm) 0–20 (cm) 20–40 (cm) Average (cm) 2013–2014 0.7 90.25 91.43 90.84 1.73 1.66 1.70 1.1 79.54 84.63 82.09 1.52 1.36 1.44 1.5 74.83 82.94 78.89 1.36 1.14 1.25 1.9 63.07 72.66 67.87 1.01 0.77 0.89 2.3 58.67 65.51 62.09 0.86 0.63 0.75 2.7 56.94 61.12 59.03 0.56 0.48 0.52 2014–2015 0.6 92.28 94.23 93.25 1.53 1.43 1.48 1.0 81.95 86.83 84.39 1.37 1.21 1.29 1.4 77.70 84.31 81.01 1.24 0.98 1.11 1.8 66.70 74.72 70.71 0.93 0.63 0.78 2.2 63.09 69.75 66.42 0.57 0.40 0.48 2.6 61.44 64.25 62.84 0.40 0.33 0.37 Values in the second, third, fifth and sixth columns are means for five growth stages; values in the fourth and seventh columns are means for 0–20 cm and 20–40 cm soil depths.