Water and nutrient, especially nitrogen nutrition, are the two key restriction factors in improving crop productivity in the Loess Plateau. Therefore, study the law of the water use, nitrogen accumulation and productivity of winter wheat under different water and fertilizer treatments are important to rational fertilization and yield improvement of winter wheat.
According to the characteristics of less and uneven seasonal distribution of precipitation and soil nitrogen shortage in the Loess Tableland, the experiment of supplemental irrigation and different nitrogen and phosphorus rates treated winter wheat was designed and simultaneously the long-term fertilization experiments were carried out. The combined method of field experiment and simulation of DSSAT model (Decision Support System for Agrotechnology Transfer) was applied to the field experiment and model simulation of crop productivity and water and nitrogen balance process of winter wheat. The main conclusions were drawn as follows:
(1) Supplemental irrigation and different fertilization had significant effects on the process of soil water balance of winter wheat, soil water content of different treatment decreased with the increasing of fertilization level. The treatment of mixed use of nitrogen and phosphorus fertilizer (NP), and mixed use of nitrogen, phosphorus and manure treatment (NPM) significantly decreased soil water content, soil water content decreased with the increasing of fertilization level. The depth of rainfall infiltration decreased with the increasing of nitrogen and phosphorus rates. Infiltration depths of CK, N, NP and NPM treatments were 220cm，200cm，180cm，160cm respectively.
Supplemental irrigation and different fertilization had significant effects on water consumption and water supply amount of soil. Water consumption and water supply amount of soil of different treatment were in the order of NPM>NP>N>CK. Different fertilization increased water consumption from 13.0 to 40.7mm than CK, NP and NPM treatment had significant difference than CK. Supplemental irrigation increased water consumption from 51.7 to143.5mm. Water consumption increased with the increasing of nitrogen and phosphorus rates, water consumption of the treatment of rain-fed and supplemental irrigation increased from 61.9 to 112.5mm and 112.1 to 183.8mm respectively.
(2)Nitrogen rates had significant influence on chlorophyll relative value (leaf SPAD values), which can increase leaf SPAD values as well as high leaf SPAD values duration. Nitrogen accumulation and nitrogen use efficiency increased with increased level of nitrogen rates and supplemental irrigation and supplemental irrigation, nitrogen rates had significant correlation between nitrogen accumulation, and nitrogen accumulation of different nitrogen rates treated wheat increased from 83.2% to 204.3% than CK, nitrogen accumulation of supplemental irrigation treatment increased 1.3% to 12.1% than rain-fed treatment.
(3) CK and N treatments both had lower crop yields, crop yields of mixed use of nitrogen and phosphorus fertilizer treatment was 168.9% higher than CK, and M，NM and NPM increase crop production more than 260%.Crop yields increased with the increasing of nitrogen and phosphorus rates, crop yields of the treatment of rain-fed and supplemental irrigation increased from 2530 to 3717 kg·hm-2 and from 2528 to 4533 kg·hm-2 respectively, however, supplemental irrigation increased crop yields from 2 to 1188 kg·hm-2 than CK. Variance analysis showed that nitrogen rates had significant effect on crop yields, however, supplemental irrigation and phosphorus rates didn’t have significant effect.
Water use efficiency (WUE) of winter wheat increased with increased level of fertilization. Water use efficiency of N, NP and NPM treatment were 42.5%，104.4% and 109.8% higher than CK respectively, NP and NPM treatment were significantly higher than CK and N treatment. Water use efficiency of winter wheat increased with increased level of nitrogen and phosphorus fertilization, from 2007 to 2008, WUE of different nitrogen and phosphorus rates were 4.2 to 7.6 kg·mm-1·hm-2 higher than CK, supplemental irrigation treatment decreased WUE from 0.2 to 2.3kg·mm-1·hm-2 than the rain-fed treatments from 2007 to 2008, which were higher than the rain-fed treatments from 2008 to 2009. Plant height, leaf area and biomass of different treatment had the same change tendency with crop yields, which increased with the increased level of fertilization level. LAI had no significant correlation with crop yields during jointing stage, during the other growth stages, plant height, leaf area and biomass had significant correlation with crop yields.
(4) The databases of weather, soil and crop growth parameter of DSSAT model in the Loess Tableland were created and used to calibrate and validate the DSSAT model. The results showed that DSSAT model was reliable in predicting wheat growth stages and crop yields.
Soil water content, nitrogen uptake dynamic and wheat production potential were simulated with DSSAT model. The results showed that soil water content, simulation results had the high degree of coincidence with measured results. The result can reflect soil water content dynamic at different soil depths and the differences between the different treatments. The seed’s nitrogen content had the best simulation result of different wheat organs, whereas the leaf nitrogen content was relatively poor. Photo-temperature productivity and climatic potential productivity were 5547~10920 kg·hm-2 and 3193~6443 kg·hm-2, respectively, and the water requirement ratio was 0.513~0.782 from 1985 to 2009, which indicates that the productivity of wheat has more promotion space on Loss Tableland.
Keywords: Loess Tableland; Water use efficiency; Nitrogen accumulation; Crop productivity; DSSAT model