Effects Of Nitrogen Application Rates On Water And Nitrogen Use And Their Physiological Basis In Wheat Under Supplemental Irrigation Based On Measuring Soil Moisture

The experiment was carried out from 2012 to 2014 under field conditions at the experimental farm of the Shandong Agricultural University. Two wheat cultivars were used including jimai20 and jimai22. Three irrigation regimes were designed for each cultivar: no irrigation(W0); 70% of soil relative water content in 0~140cm soil layers at jointing+70% at anthesis in the period from 2012 to 2013 and 70% at jointing and 65% at anthesis in the period from 2013 to 2014(W1); irrigation water of 60 mm at jointing and anthesis respectively(W2). Under different irrigation regime, four N application rates were designed: 0(N0), 180(N1), 210(N2) and 240(N3) kg N ha-1. The experiment utilized the split-plot design with 3 replications. In order to study effects of nitrogen application rates on water and nitrogen use and their physiological basis in wheat under supplemental irrigation based on measuring soil moisture, the main results as follow:1 Under supple mental irrigation based on measuring soil moisture, effect of different N application rates on water consumption characteristics and yield of wheat 1.1 Effect of different treatments on water consumption characteristics of wheat In the period from 2012 to 2013, under the W1 condition, the total supplemental irrigation(SI) amount of N2 was significantly greater than that of N0 and N1, but there was no significant difference between N2 and N3 in jimai20; the total SI amount of N3 was lower than that of N0, but greater than that of N1 and N2 in jimai22. Under the W0, W1 and W2 conditions, the soil water consumption and percentage of soil water consumption to total water consumption amounts in N2 was higher than those of N0, N1 and N3 in two wheat cultivars. Under the W0 condition, soil water consumption in N2 in 40 to 160 cm soil layers was significantly greater than that in N0 and N1, but there was no significant difference between N2 and N3 in two wheat cultivars; under the W1 and W2 conditions, soil water consumption in N2 in 60 to 140 cm soil layers was significantly greater than that in other treatments. The water consumption of N2 was higher than that of N0, N1 and N3 from jointing to maturity. It indicated that N2 treatment promoted the use of soil water in the 60~140 cm soil layers, with higher amounts of water consumed fom jointing to maturity. The N2 treatment also was beneficial for meeting the water demand after the jointing stage. In the period from 2013 to 2014, under the W1 condition, the total SI amount of N3 was significantly greater than that of N0 and N1, followed by N2 in jimai20, the total SI amount of N0 was significantly greater than that of N1 and N2, but there was no significant difference between N0 and N3 in jimai22. Under the W1 and W2 conditions, the soil water consumption and percentage of soil water consumption to total water consumption amounts in N2 was significantly higher than those of N0, N1 and N3 in two wheat cultivars; soil water consumption in N2 in 60 to 140 cm soil layers was significantly greater than that in other treatments. The water consumption of N2 was higher than that of other treatments from jointing to maturity. It indicated that N2 treatment promoted the use of soil water. 1.2 Effect of different treatments on carbon metabolism of wheat In the period from 2012 to 2013, under the W1 condition, the net photosynthesis rate, transpiration rate and stomatal conductance of flag leaves under the N2 treatment was greater than that of flag leaves under other treatments from 14 to 28 days after anthesis(DAA) in two wheat cultivars. The actual photochemical efficiency, electron transport rate and photochemistry quenching index of N2 were highest at 7 DAA and 14 DAA. The sucrose and SPS activity of N2 were significantly greater than those of N0 and N3 from 14 to 28 DAA in two wheat cultivars, which indicated that N2 treatment promoted the transformation of light energy into chemical energy and was benefit for the accumulation of carbohydrate. In the period from 2012 to 2013, under the W0 conditions, dry matter accumulation amounts and dry matter accumulation a mounts in grain at maturity of N2 was greater than those of N0 and N1, but there was no significant difference between N2 and N3 in two wheat cultivars; dry matter translocation amounts from vegetative organs to grain and its contribution to grain after anthesis in N2 were higher than those in other treatments in two wheat cultivars. Under the W1 and W2 conditions, dry matter translocation amounts from vegetative organs to grain and its contribution to grain after anthesis at maturity in N2 were significantly higher than those in other treatments in two wheat cultivars. In the period from 2013 to 2014, under the W1 and W2 conditions, dry matter accumulation amounts and dry matter accumulation amounts in grain were highest in N2 in two wheat cultivars, dry matter translocation amounts from vegetative organs to grain and its contribution to grain after anthesis in N2 were significantly higher than those in other treatments in two wheat cultivars. It indicated that N2 treatment promoted the translocation of dry matter accumulation in grain, which is conducive to increasing grain yield. 1.3 Effect of different treatments on nitrogen metabolism of wheat In the period from 2012 to 2013, under the W1 condition, the nitrogen accumulation amounts in grain at maturity of N2 was greater than that of N0 and N1, but there was no significant difference between N2 and N3 in two wheat cultivars; the nitrogen translocation amounts from vegetative organs to grain and its contribution to grain after anthesis in N3 was lower than those in N2, but higher than N0 and N1 treatments. It indicated that N2 treatment promoted the nitrogen accumulation at maturity and was benefit for the nitrogen translocation from vegetative organs to grain. In the period from 2013 to 2014, under the W1 condition, the nitrogen accumulation amounts in grain at maturity of N2 was significantly greater than that of N0 and N1, but there was no significant difference between N2 and N3 in two wheat cultivars. Under the W0 and W2 conditions, the nitrogen translocation amounts from vegetative organs to grain and its contribution to grain after anthesis in N2, followed by N3, was the highest; under the W1 condition, the nitrogen translocation amounts from vegetative organs to grain and its contribution to grain after anthesis in N2 was greater than those in N0 and N1, but there was no significant difference between N2 and N3 in jimai20, the nitrogen translocation amounts from vegetative organs to grain and its contribution to grain after anthesis in N2 was significantly greater than those in other treatments. It indicated that N2 treatment promoted the nitrogen translocation from vegetative organs to grain, and improved the nitrogen accumulation in grain. 1.4 Effect of different treatments on senescence of flag leaf and root activity In the both growing seasons, under the W1 condition, the activity of superoxide dismutate(SOD) and catalase(CAT) in N2 was higher than that of N0 from 0 DAA to 7 DAA, but there was no significant difference between N2 and N3. The activity of SOD and CAT inN2 was higher than that of N0 and N3 from 14 DAA to 28 DAA. The malondiadhyde content(MDA) in N0, followed by N3, was the highest; MDA of N2 was the lowest from 21 DAA to 28 DAA. The soluble protein concentration of N2 was higher than t hat of N0 and N3 from 7 DAA to 28 DAA. It indicated that N2 treatment increased the activity of SOD and CAT in flag leaf after anthesis and soluble protein concentration that i mproved the ability of scavenging reactive oxygen species of flag leaves and ability of osmotic regulation, which was benefit for reducing the damage of the cell membrane structure, and maintained a higher level of cell metabolism and delays the senescence of flag leaves. In the period from 2012 to 2013, under the W1 condition, the root activity of N2 was higher than that of N0 at anthesis in jimai20, but there was no significant difference between N2 and N3; the root activity of N2 was significantly higher than that of N0 and N3 at anthesis in jimai22. In the period from 2013 to 2014, under the W1 condition, the root activity of N2 was significantly higher than that of N0 and N3 at anthesis in two wheat cultivars, which indicated that N2 treatment increased the root activity at anthesis, and was benefit for the growth of wheat after anthesis. 1.5 Effect of different treatments on grain yield and water use efficiency In the period from 2012 to 2013, under the W0 and W2 conditions, the grain yield of N2 was greater than that of N0 and N1, but there was no significant difference between N2 and N3 in two wheat cultivars; there was no significant difference between N1, N2 and N3 in water use efficiency(WUE) in two wheat cultivars. Under the W1 condition, the grain yield and WUE of N2 were significantly greater than those of other treatments in two wheat cultivars. It indicated that N2 was the optimum treatment for obtaining higher grain yield and WUE. In the period from 2013 to 2014, under the W0 condition, the grain yield of N2, followed by N3, was the highest in two wheat cultivars; there was no significant difference between N1, N2 and N3 in WUE in two wheat cultivars. Under the W1 and W2 conditions, the grain yield of N2 was significantly greater than those of other treatments in two wheat cultivars; there was no significant difference between N1, N2 and N3 in WUE in jimai20, WUE of N2 was highest, which indicated that the optimal nitrogen application rate under the experimental conditions was 210 kg ha-1.2 Under the same N application rates, effect of water treatments on grain yield, water use efficiency and nitrogen productivity efficiency In the period from 2012 to 2013, under the N0 and N1 conditions, the grain yield and WUE of W1 were greater than those of W0 in two wheat cultivars, but there was no significant difference between W1 and W2. Under the N2 and N3 conditions, the grain yield and WUE of W1 were significantly greater than those of other treatments in two wheat cultivars. It indicated that W1 treatment was the optimum treatment for obtaining higher grain yield and WUE under the N2 and N3 conditions. In the period from 2013 to 2014, under the N0 and N1 conditions, the grain yield and WUE in W1, followed by W2, were highest in two wheat cultivars. Under the N2 conditions, the grain yield and WUE of W1 were significantly greater than those of other treatments in two wheat cultivars. Under the N3 conditions, the grain yield of W1 was highest in two wheat cultivars, the WUE of W2 was highest, but there was no significant difference between W1 and W2. It indicated that W1 treatment was the optimum treatment under the experimental conditions.3 Evaluation of water consumption and grain yield in two wheat cultivars 3.1 Water consumption characteristics in two wheat cultivars In the both growing seasons, under the N2W1 and N3W1 conditions, SI amount at anthesis and total SI amounts in jimai20 were significantly higher than those in jimai22; the soil water consumption amounts and the percentage of soil water consumption amounts to total water consumption amounts in jimai22 were higher than those in jimai20; total water consumption amounts from jointing to anthesis in jimai22 were significantly higher than that in jimai20. Under the N0W1 condition, the soil water consumption amounts from the 20 to 140 cm soil layers in jimai22 was significantly higher than that in jimai20. Under the N1W1, N2W1 and N3W1 conditions, the soil water consumption amounts from the 60 to 140 cm soil layers in jimai22 was significantly higher than that in jimai20. These results suggested that jimai22 was benefit for the use of soil water in the 60~140 cm soil layers and meeting the water demand after the jointing stage. 3.2 Carbon metabolism in two wheat cultivars In the period from 2012 to 2013, the dry matter accumulation at jointing, anthesis and maturity in jimai22 was significantly higher than those in jimai20. In the both growing seasons, under the N0W1, N2W1 and N3W1 conditions, dry matter translocation amounts from vegetative organs to grain and its contribution to grain after anthesis in jimai22 was significantly greater than those in jimai20; under the N1W1 condition, dry matter translocation amounts from vegetative organs to grain and its contribution to grain after anthesis in jimai22 was higher than those in jimai20, which indicated that jimai22 was benefit for improving dry matter accumulation amounts after jointing, whose dry matter translocation amounts from vegetative organs to grain and its contribution to grain after anthesis was higher. Jimai22 is conducive to obtaining higher gain yield. 3.3 Nitrogen translocation amounts from vegetative organs to grain in two wheat cultivars In the period from 2012 to 2013, under the N0W1 and N1W1 conditions, the nitrogen accumulation amounts in vegetative organs at maturity, the nitrogen translocation amounts from vegetative organs to grain and its contribution to grain after anthesis in jimai22 were significantly higher than those in jimai20. Under the N2W1 and N3W1 conditions, the nitrogen accumulation amounts in vegetative organs at maturity in jimai22 were significantly higher than those in jimai20; the nitrogen translocation amounts from vegetative organs to grain and its contribution to grain after anthesis in jimai22 were greater than those in jimai20. It indicated that jimai22 is conducive to the nitrogen translocation from vegetative organs to grain and its contribution to grain after anthesis, whose the nitrogen accumulation amounts in grain was higher. 3.4 Grain yield and water use efficiency in two wheat cultivars In the both growing seasons, under the N0W1 conditions, the grain yield in jimai22 was greater than that in jimai20; there was no significant difference in WUE between jimai20 and jimai22. Under the N1W1, N2W1 and N3W1 conditions, the grain yield and WUE in jimai22 were significantly higher than those in jimai20, which indicated that jimai22 was wheat cultivar that for obtaining higher grain yield and WUE.