Effects Of Application Of Phosphorus Combined With Nitrogen Fertilizer On Grain Yield And Quality In Wheat And The Physiological Basis

In order to explore effects of application of P combined with N fertilization on yield and quality of wheat and their physiological bases, studies on absorption and transportation of N, protein formation, production and transportation of photosynthetic products and starch formation of strong-gluten Gaocheng8901(GC8901) and weak-gluten Shannong1391(SN1391) were conducted on low-fertility soil. A field fertilization experiment included treatments of P2O5 0 kg/hm2 ( P0 ), P2O5 120 kg/hm2 ( P120 ) and P2O5 240 kg/hm2 ( P240 ) respectively under N 0 kg/hm2 ( N0 ) and N 225 kg/hm2 ( N225 ). Crop growth and development, physiological biochemistry and some key enzymes were analysed. The main results were as follows:1 Effect of application of phosphorus combined with nitrogen fertilization on grain yield and its components of wheatThe number of ears per unit area increased with increasing fertilization amount of phosphorus. However, the order of the number of grains per ear and 1000-grain weight was P120 > P240 > P0. Grain yield per unit area increased with increasing fertilization amount of phosphorus.The number of ears per unit area, the number of grains per ear and 1000-grain weight of N225 were all higher than those of N0. Yield of N225 was significantly higher than that of N0. Analyses showed the significant effects of nitrogen, phosphorus, variety and its interaction on yield.2 Effect of application of phosphorus combined with nitrogen fertilization on quality of wheat2.1 Protein and their components Contents of albumen and globulin increased gradually with increasing fertilization amount of phosphorus. For GC8901 under N225, contents of gliadin, glutenin, and the total protein increased at first and then decreased with increasing fertilization amount of phosphorus. For GC8901 under N0 and SN1391 under N0 and N225, contents of gliadin, glutenin, and the total protein decreased gradually with increasing fertilization amount of phosphorus. Contents of total protein and its components of N225 were higher than those of N0 except GC8901 under P0. For GC8901 under N225, the ratio of albumen and globulin decreased at first and then increased with increasing fertilization amount of phosphorus, and the proportion of gliadin and glutenin increased at first and then declined. For GC8901 under N0 and SN1391 under N0 and N225, the ratio of albumen and globulin increased gradually, and the ratio of gliadin and glutenin decreased gradually.2.2 Farinograph parametersFor GCg8901 under N225, the mixing tolerance index reduced, and the water absorption percentage, dough development time, stability time and evaluation value increased with increasing fertilization amount of phosphorus. For GC8901 under N0 and SN1391 under N0 and N225, the mixing tolerance index increased, and the water absorption percentage, dough development time, stability time and evaluation value reduced with increasing fertilization amount of phosphorus. Values of the water absorption percentage, development time, stability time and evaluation value of N225 were higher than those of N0, and the mechanical tolerance index was lower than that of N0, not including GC8901 under P0. 2.3 Extensograph parametersFor GC8901 under N225, gluten strength increased with increasing fertilization amount of phosphorus, which was helpful to improve extension ability to a certain extent. For GC8901 under N0 and SN1391 under N0 and N225, stretch area, stretch resistance and stretch ratio diminished by degrees with increasing fertilization amount of phosphorus. Gluten strength and extension ability of N225 was better than that of N0. Gluten strength of GC8901 increased more, and extension degree of SN1391got better.2.4 Starch and its componentsThe order of contents of amylose, amylopectin and total starch was P120 > P240 > P0 with increasing fertilization amount of P. Under N0, the ratio of amylase to amylopectin rose with increasing fertilization amount of P. The ratio GC8901 under N225 was P120P240>P0 with increasing fertilization amount of P. Peak viscosity, trough viscosity, breakdown, final viscosity and set back of N225 were higher than those of N0 except GC8901 under P0.3 Effects of application of P combined with N fertilization on nitrogen metabolism and protein formation3.1 Effects on accumulation, distribution and transportation of nitrogenN content of plant: For GC8901 under N225, total N content of flag leaf and nutritive body of ear in GC8901 order with P120>P240>P0 during the period of early fiilling stage. For GC8901 under N0 and SN1391 under N0 and N225 total N content of all organs decreased. A significant positive correlation between N content of flag leaf and grain protein content was found at anthesis.Plant nitrogen accumulation and transportation: For GC8901 under N225 N-accumula- tion amount, amount of stored N translocation, rate of stored N translocation, amount of N assimilation after anthesis and contribution of assimilated N increased with increasing fertilization amount of P. For GC8901 under N0 and SN1391 under N0 and N225 P fertilization increased N-accumulation amount, amount of stored N translocation, rate of stored N translocation increasing, however amount of N assimilation after anthesis with less increasing. Under P120 and P240, rate and amount of stored N translocation of N225 was higher than those of N0, and amount of N assimilation and contribution of assimilated N increased after anthesis. Correlation analysis showed that an increase in grain protein content needed a coordinate increase in contribution of assimilated N before and after anthesis.3.2 Effect on nitrogen metabolism of plantFor GC8901 under N225, the order of key enzymes of N assimilation NR and GS, protein hydrolase enzymes endopeptidase and carboxypeptidase of flag leaf, and Free amino acid content of grain was P120 > P240 > P0. For GC8901 under N0 and SN1391 under N0 and N225, NR, GS, CP, EP of flag leaf, free amino acid content of grain and flag leaf decreased with increasing phosphorus amount. The results from this study showed that P fertilization under higher level of N fertilization could facilitate N metabolism to a certain extent for GC8901, that response of N metabolism of both the varieties to the ratio of N and P was different. For both the varieties, activities of key enzymes of N metabolism and free amino acid content of grain and flag leaf of N225 were higher than those of N0.3.3 Grain protein contentBefore mid grain filling, grain protein content of both the varieties at the two nitrogen levels increased with increasing fertilization amount of P. Then under N225 the content of Gaocheng 8901 of P240 increased by a smaller margin than that of P120. At harvest, the content of P120 was the greatest and that of P0 was the smallest. For Gaocheng 8901 under NO and Shannong 1391 under NO and N225, the content decreased by a big margin with increasing fertilization amount of P at mid grain filling, the content increased by a small margin at late stage, and finally the content decreased with increasing fertilization amount of P. For both the varieties under all the phosphorus amounts and at all the stages, grain protein content of P225 is higher than that of P0.P fertilization increased grain protein accumulation amount increasing. Grain protein accumulation amount of N225 was greater than that of N0.4 Effect of application of P combined with N fertilization on photosynthetic characteristics of flag leaf and formation of grain starch4.1 Photosynthetic rate and chlorophyll fluorescence parameters of flag leafP and N fertilization increased chlorophyll content, photosynthetic rate, Fv/Fm,ΦPSⅡof flag leaf and decreased NPQ with a clearer effect from P0 to P120. The effect of N225 was more significant than that of N0.4.2 Accumulation, distribution and transportation of dry matterAccumulation of dry matter per unit area increased with increasing the dosage of phosphorus. Amount of dry matter of N225 was bigger than that of N0. Amount of dry matter of flag leaf, other leaves, stem, sheathe and ear increased, their percentages was decreased, and grain weight and its percentage increased with increasing fertilization amount of P. Amount of dry matter of various organs of N225 was bigger than those of N0. For P0, the ratios of nutritive organs increased, but the proportion of seed decreased. However, For P120 and P240, the opposite was true.As compared with P0, P fertilizer increased amount of dry matter translocation before anthesis, decreased contribution of dry matter translocation before anthesis, increased amount of dry matter accumulation and contribution of dry matter accumulation translocation after anthesis, which indicated that p fertilization was more beneficial to increasing production of dry matter after anthesis and led to an increase in grain yield. N fertilization increased amount of dry matter translocation before anthesis, amount of dry matter accumulation after anthesis, contribution of dry matter accumulation after anthesis, but it decreased contribution of dry matter translocation before anthesis, which suggested the fact that N fertilization could facilitate an increase in grain yield.Interaction between nitrogen and phosphorus was found. In accumulation, distribution and transportation of dry matter, differences between various phosphorus treatments under N0 were smaller. However, differences in these ways between various phosphorus treatments under N225 were bigger.4.3 Starch content of grainUnder p fertilization, the order of starch content, its component content and its accumulation amount was P120>P240>P0, but differences in the contents between P120 and P240 were small. Differences in the contents between various phosphorus treatments under N0 were small, but the differences between various phosphorus treatments under N225 were big. Starch content and its accumulation amount of Shangnong1391 increased by a bigger margin than those of Haocheng8901. Under P0, Starch accumulation amount of N225 was less than that of N0. Under P120 and P 240, Starch accumulation amount of N225 was less than that of N0. The results from this study showed that N fertilization under sufficient phosphorus could facilitate starch accumulation of grain, but N fertilization under P-deficiency condition could decrease the accumulation.