| Wheat and maize are important grain crops grown worldwide. In China, these crops are mostly grown in north china plains (NCP). The water and nutrient content in the soil are two main factors that affect crop yield and quality. Nitrogen is the main elemental component of nutrient management for crop production; its injudicious use is widely reported in wheat-maize cropping system of NCP. Due to conversion of nitrogen in different forms when it is applied beyond to absorption capacity by plants, it evaporates in to atmosphere or, leaches down into the soil. This results not only economic losses but also pollutes air and adversely affect the underground water quality. Nitrogen losses are further enhanced by warming and infrequent rainfall conditions of this area. So, judicious use of N and water is prerequisite for improving their use efficiencies to sustain high yields of wheat and maize under changing climatic conditions.A two-year field study was conducted in randomized complete block design on sandy loam soil at the experimental farm of Chinese Academy of Agricultural Sciences (39°60’27"N,116°60’09"E) at Lang fang in the growing seasons of2011-12and2012-13. The main objectives of current study were to determine the effect of N fertilization and water levels on growth, dry matter and yield production of wheat and maize and to investigate the N accumulation in the soil and various parts of plants under changing climatic conditions. Four rates of fertilizers (F0=NO P0K0, F1=N120P84K120, F2=N240P168K240, F3=N360P254K360kg ha-1) and five water level (W1, W2, W3, W4and W5) were applied to both crops. Irrigation water treatments for wheat were W1(250.00mm), W2(316.67mm), W3(383.33mm) and W4(483.33mm) and for maize were W1(233.33mm), W2(333.33mm), W3(466.67mm) and W4(616.67mm). These irrigated treatments (W1, W2, W3, and W4) were protected from rainfall with moveable shelter, while rainfall water treatment (W5) was placed in open zone to intercept rain water for both wheat and maize.The results showed that leaf dry matter of wheat at anthesis stage was significantly increased at increasing water and nitrogen levels in both growing seasons (2011-2012and2012-2013). During2012-13spike dry matter was significantly varied at all water levels and nitrogen treatments. However, W4at Fl produced higher yield. The similar trend was observed for stem and root dry matter production. In the first growing season2011-12all water and fertilizers combination levels showed non-significant response. However, in second growing season2012-13, W4at F3level revealed maximum stem and root dry matter production. Generally a trend of dry matter accumulation at wheat anthesis was found in the order of stem>spike>leaf>root. Moreover, same water and fertilizer combination significantly influenced dry matter yield of all investigated parts of wheat crop at harvesting stage during both the growing seasons. Highest grain dry matter was recorded in W4at F3level during2011-12followed by F2of W4and F2of W3, respectively, whereas, it was higher in F2of W3during2012-13. In both growing seasons, W4at F3level produced significantly higher values for chaff dry matter. For stem dry matter production, F3at W4level, showed maximum values in2012-13. Combination of F3and F4at W4level during2011-12proved best for the production of root dry matter. At wheat harvest the order of dry matter accumulation was grain>stem>chaff>root>Leaf.1000kernel weight was higher in all treatments during2011-12compared to2012-13but there was non-significant response among treatments. In maize, at silking stage, maximum leaf and cob dry matter was recorded in W5at F2, followed by F3and F1during2012. Similarly, higher dry matter of root was also measured in W5at F3level. Grain dry matter of maize was observed higher in F3and F2of W5, which also was higher in F2of W3, F2, Fl and F3of W4, respectively during2012than or compare to other water and fertilizers combination levels. Dry matter accumulated in the order of stem>leaf>root>cob at maize silking stage and at harvesting stage order of dry matter accumulation was grain>stem>cob straw>leaf>root. There was non-significant effect of N and water levels on plant height; however, higher grain yield was recorded at increasing level of water and N rate.N uptake and accumulation in various parts of wheat and maize were investigated at anthesis/silking and harvesting stages. In addition, nitrogen translocation (NT), nitrogen translocation efficiency (NTE), contribution of pre-anthesis/silking nitrogen to grain nitrogen (CNS) and nitrogen harvest index (NHI) were also measured. On average, total N uptake and accumulation were increased by irrigation and N fertilization in the second growing season2012-13in both crops. In wheat, most fertilizer N was taken up from at anthesis; then it either stabilized or slightly declined, while soil N contributed further to plant N uptake. At wheat anthesis order of nitrogen accumulation was stem>leaf>spike>root and at wheat harvest nitrogen accumulated in the order of grain>stem>chaff>root>leaf. In maize, N uptake was stabilized both in silking and harvesting stage. At maize silking order of N accumulation was leaf>stem>cob>root and N accumulated in order of grain>leaf>stem>root>cob straw at maize harvest. Compared to rain-fed conditions, more soil and fertilizer N was utilized by the irrigated crop under the irrigation treatments, particularly in2012-13. N parameters including NT, NTE, CNS, and NHI were significantly affected by water and N fertilizers levels. The higher values for these parameters were obtained at increasing N fertilizers levels under all water levels. These results indicated that nitrogen fertilization and irrigation affected the uptake and translocation of nitrogen. Thus, supplemental irrigation, applied at a sensitive growth stage, would be a valuable management practice for improving water-use efficiency and crop N uptake under the dry conditions. Moreover, both factors (water and N fertilization) greatly affect their efficiencies, hence efficient use of these factors will help to reduce the excess use of water and nitrogen input and increases the sufficient net income.Nitrogen content in the soil was calculated; results showed that the highest concentrations of ammonium N were accumulated in0-20cm surface layer of soil profile regardless of water and fertilizer levels, type of crop and year. The water and fertilizer combination of W5F4showed highest accumulations after the harvest of wheat2012and wheat2013, whereas W5F3and W3F4revealed maximum accumulation of NH4-N after the harvest of maize2012and maize2013respectively. Nitrate N accumulations in all depths increased with increasing rate of N in each fertilizer dose despite of crop and year. Fertilizer treatments had the significant effect on nitrate content of soil. The unfertilized plots showed the lowest and the fertilizer N treated plots revealed the highest nitrate concentration with irrigation water. Mineral N content more or less followed the trend of nitrate N accumulation in soil layers as nitrate contributed major proportion of mineral nitrogen.Soil water content before sowing of each crop varied significantly due to irrigation levels and rainfall. The most economical N rates and irrigation levels were lower than the maximum N rates and irrigation levels required for maximum yield. Nitrogen application rate of225-328kg ha-1and475-638mm water were found to be better combination for getting economical yield4849-8837kg ha-1of wheat. Maize produced better yield9466-11462kg ha-1by utilizing economical nitrogen amout of248-345kg ha-1and834-1163mm water. In both years, crop water use (evapotranspiration) was linearly related to the amount of irrigation. The WUE decreased with increasing irrigation application rates. The low irrigation treatment had higher WUE than that of high irrigation treatment. In both years, the WUE increased significantly with nitrogen application rates up to rate of240kg ha-1. The N240treatment had the highest WUE among the various N treatments. Nitrogen use efficiency increased with increasing water application and decreased with increased nitrogen application levels. In all crop seasons lowest values of nitrogen use efficiency were noted in highest fertilizer (F3) and lowest water (W1) treatment combination.In conclusion, the present study provided evidence that proper N fertilization and irrigation management are important strategies to offset climate change effects and to get reasonable yield of wheat and maize with improved WUE and NUE. |
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