Responses Of Grain Yield And Phosphorus Efficiency Of Wheat Cultivars Released In Different Decades To Soil Fertility Levels In Guanzhong Plain, Shaanxi

Wheat cultivars replacement is one of the im portant factors to increase wheat yield, but how phosphorus efficiency responses to wheat cultivars replacement is rarely rep orted. In order to understand the responses of yield and phosphorus efficiency of winter wheat cultivar improvement to various soil fertility levels, we investigated grain yield, yield components and phosphorus physiological efficiency of winter wheat cultivars released in 1980 s, 1990 s and recent years under different soil fertility leve ls,which have been built up in a lon g-term fertilization experiment on manural loess soil in Guanzhong Plain, Shaanxi province, China. The long-term experiment included nine treatments, i.e. control(CK, no nutrient input), two doses of manure am endment(M1,M2),two doses of chemical fertilizers of nitrogen and phosphorus((N1P1,N2P2) and the in tegrated application of m anure and chemical fertilizers of nitrogen(N) and phosphorus(P), both at two doses(M1N1P1, M1N2P2, M2N1P1, and M2N2P2). The tested winter wheat cultivars were named as Xiaoyan 6(extensively grown variety in 1980s), Xiaoyan 22(extensively grown variety in 1990s) and Xinong 979(variety in recent years).The main results obtained were as follows:1) With the sam e seedling am ount, the population sizes o f winter wheat cu ltivar at different growth stages were not significant different, while the spike number of Xinong 979 was the highest at m aturity; In addition, population and spike num ber of wheat on MNP treatments are sign ificantly higher than oth er treatments. During c ultivar development process, at lower soil fertility conditions spike number per unit area was higher for Cultivar Xiaoyan 6 than for Cultivar Xiaoy an 22, but the curren t cultivar Xinong 979 yielded the highest spike num ber; under high soil fertilit y, however, the spike number per unit area tended to be increased with cultivar im provement. In addition, grain num ber per spike showed the inconsistent trends with cultivar development at low soil f ertility levels, but the general increasing trend was dete cted at high soil fertility levels. The 1000 grains weight showed an increasing trend with improvement of cultivars at all te sted fertilizer treatments. Similar to grain yield, increases in soil fertility or nutrients input also enhanced the spike number per unit area, grain num ber per spike and the weight of 1000 grains, respectively, regardless of cultivars. Wheat yield generally showed a tendency of progressive increase with the improvement of cultivar, it also be significantly enhanced with increasing soil fertility regardless of cultivars. Nevertheless, pronounced yield increases due to cultivar improvement were only observed on soils with high fertility such as MNP treatments, while yield benefit was minor on low fertility soils(e.g. CK, M or NP treatments).2) Winter wheat cultivar development had no significant ef fects on phosphorus concentrations of winter wheat plant a nd phosphorus uptake of above ground biom ass at different growth stages. Phosphorus concentr ations of wheat plant decreased with the development of wheat growth, while phosphor us uptake amount increased. The phosphorus concentrations of wheat plant and phosphorus uptake on M and MNP treatments were higher than those of CK and NP treatments. There is no sign ificant effects of wheat cultivar development on pre-anthesis and post-anthesis P accumulation under different soil fertility levels. Regardless of variety, pre-anthesis P accumulation increased significantly with the increase of nutrient inputs or soil f ertility, while post-an thesis P accumulation was not obvious. Ratio between pre-and po st-anthesis P accumulant increased with wheat cultivar development under MNP, but no obvious trend wa s detected in other treatments. With the increase of the fertility ratio between pre-and post-anthesis P accumulant increased regardless of cultivars. Therefore, the cultivar or f ertility improvement promoted pre- anthesis phosphorus uptake of wheat.3) The variation of phosphorus physiologi cal efficiency was 128~341 kg/kg, and the phosphorus balance index was 65~314 % under tested condition. With winter wheat cultivar development, phosphorus physiological ef ficiency and balance index showed in order Xiaoyan 22> Xinong 979> Xiaoyan 6. Phosphorus physiological ef ficiency is higher, phosphorus balance index is lower on NP treatments; phosphorus physiological efficiency is lower, phosphorus balance index is higher on M treatments; the phosphorus physiological efficiency was higher and the balance index was close to 1 on MNP treatments.4) Winter wheat cultivar development did not affect the soil P balance significantly. All varieties in M or MN1P1 treatm ents shown nagetive balance, and NP or MN2P2 treatm ent shown positive or neutral balance. In term s of the annual soil phosphorus balan ce in th e experiment, M2N2P2 treatment almost kept the P balance.On the whole, pronounced yield increase s due to cultivar im provement were only observed on soils with high fertility such as MNP treatments, which m anifested by the increase in the weight of 1000 grains and spike number per unit area for cultivar Xinong 979 and grain num ber per spike and weight of 1000 grains fo r cultivar Xiaoyan 22. The phosphorus physiological ef ficiency and phos phorus balance index were im proved with wheat cultivars improvement and with th e increase of soil f ertility and nutrient inputs. In addition, winter wheat cultiv ar improvement did not affect the Soil P balance significantly. Hence, the synergistic increases in yield and P efficiency as a result of cultivar improvement can be achieved only on soils of high fertility, but not on low fertility soils. It is neces sary to improve soil fertility to m atch the featur e of current w heat cultivar on the one hand, meanwhile wheat breeding should take the adaptation of new cultivars to the low soil fertility into consideration to fully explore yield potential of the given cultiv ar on the other hand in the region. Although som e conclusions on whe at yield and P efficiency obtained from this test related to wheat cultivars development at different soil fertility gradient, further research is needed to fully understand the mechanism s to serve for developing the new variety and reasonable and efficient fertilization.