|Other Abstract||Nutrient management plays a very important role in wheat production. Crop straw is not only an important source of soil organic carbon, but also an important source of agricultural nitrogen. Phosphorus fertilizer is the main source of agricultural phosphorus, and its effectiveness is low. Mineralization of organic phosphorus has become an important source of phosphorus uptake by plants (Zhao S H et al., 2004). However, the availability of straw nitrogen and organic phosphorus to crops may vary with different genotypes, which depends on the interaction between the important underground organ root and soil. At present, there is a lack of research on root organic nutrient uptake efficiency of spring wheat varieties.
This paper studies on the effect of different varieties on root N and Puptake in spring wheat. The pot experiment had a two-factorial design: 2 N addition levels (with and without urea) ×6 wheat cultivars (wheat was grown in soils with 15N-labeled maize straw added);3 P addition levels (with KH2PO4, with Phytate-Na, without P fertilization) ×6 wheat cultivars. The three spring wheat cultivars of Jinbaoyin (JBY), Heshangtou (HST) and Dingxi-24(DX-24) are referred to as ‘‘old cultivars’’and the other three cultivars Longchun-30(LG-30), Nabuq-6(N-6) and Ganchun-27(GC-27) as ‘‘modern cultivars’’. The distribution of photosynthetic products, root characteristics and absorption of nitrogen and phosphorus were measured at anthesis and maturity. The main results are as follows:
1. Three modern varieties (Longchun-30, Nabuq-6, Ganchun-27) and one old variety (Heshangtou) had high harvest index, small root ratio and better grain yield, which was attributed to the more preferential distribution of photosynthetic products from vegetative organs to grains. Breeding work increased the allocation of biomass from roots to aboveground parts.
2. The root biomass, root length density and root specific surface area of modern varieties(Longchun-30, Nabuq-6, Ganchun-27) were smaller than those of old varieties(Jinbaoyin, Heshangtou and Dingxi-24) at anthesis and maturity stages. The root mean diameter of modern varieties was basically the same as that of old varieties at anthesis stage, and the root mean diameter of modern varieties was larger than that of old varieties at maturity stage. The root biomass, root length density, root mean diameter and root specific surface area at mature stage were all lower than those at anthesis stage.
3. There were differences in N uptake between maize straw and other nitrogen sources (soil and fertilizer). However, there was no correlation between these differences and the root parameters measured among the six varieties. The total N uptake efficiency (total N uptake per unit root weight or root length) of modern varieties was higher than that of old varieties under different N fertilization levels at anthesis stage. At maturity stage, the root N uptake efficiency of three modern varieties was 292-336 mg N g-1, 3.2-4.0 mg N m-1, while that of three old varieties was 132-213 mg N g-1, 0.93-1.6 mg N m-1. The N uptake efficiency (unit of root weight or root length) of modern varieties was higher than that of old varieties, and had nothing to do with urea fertilization. Urea application increased soil nitrogen availability, significantly increased the nitrogen uptake of maize straw, but had little effect on the total N auptake efficiency among varieties.
4. The nitrogen transfer amount, nitrogen transfer efficiency and contribution rate of nitrogen transfer to grain nitrogen of different varieties were significantly improved with increasing urea application. Without urea, the modern varieties (Longchun-30, Nabuq-6, Ganchun-27) significantly higher than old varieties (Jinbaoyin, Heshangtou, Dingxi-24). With urea, the differences among varieties were disparity decreases, but the performance of modern varieties (Longchun-30, Nabuq-6, Ganchun-27) and Heshangtou were still higher than Jinbaoyin and Dingxi-24.
5. The grain yield of Dingxi-24 was the lowest under KH2PO4 and Phytate-Na treatments, and its harvest index was also lower than other varieties;the aboveground biomass and phosphate fertilizer utilization efficiency of Heshangtou were significantly higher than other varieties. Phosphorus application increased grain yield, and the difference was significant due to different genotypes. There was a positive correlation between harvest index and nitrogen and phosphorus harvest index. The P harvest index of modern varieties and Heshangtou were higher than that of old varieties. In low available phosphorus production area, high harvest index is the guarantee of grain yield.
6. There were no significant differences in root biomass, root shoot ratio, root length density and root specific surface area between cultivars at anthesis stage and KH2PO4 application. The results showed that the root biomass, root length density and root specific surface area of modern varieties were smaller than those of old varieties under the treatment of Phytate-Na fertilizer at anthesis stage and phosphorus application at maturity stage. The average root diameter of modern varieties and old varieties were basically the same at anthesis and maturity. P application reduced the root shoot ratio of wheat, and the effect of KH2PO4 and Phytate-Na was the same.
7. There were significant differences in phosphorus concentrations in stems, leaves and grains due to different phosphorus sources and varieties. Phosphorus application increased the contents of nitrogen and phosphorus in grains, and the differences among varieties were significant. Dingxi-24 had the highest concentration of nitrogen and phosphorus, but the N, P of grain lowest. There was a significant negative correlation between nitrogen concentration and yield, and the contradiction between yield and quality was prominent. Phosphorus application increased the nitrogen and phosphorus contents of aboveground plants, which showed that the nitrogen and phosphorus contents of modern varieties and Heshangtou were more than the other old varieties.
8. There was no significant difference in nitrogen and phosphorus uptake efficiency among cultivars at anthesis stage. On average cultivar, the root N and P uptake efficiency of KH2PO4 was significantly higher than that of the other two treatments. At maturity, the root N and P uptake efficiency of Longchun-30 was significantly higher than that of other varieties. Phosphorus application, especially inorganic phosphorus, increased the availability of soil phosphorus, and significantly improved the root N and P uptake efficiency of various varieties.
In conclusion, the effects of nitrogen and phosphorus on grain yield, root biomass and root characteristics of wheat are different with different varieties. Breeding is a process of increasing grain yield, reducing root biomass, root length density and root specific surface area, and improving root nutrient uptake efficiency. This provides a reliable theoretical support for the breeding of varieties with different demands in specific agricultural systems.|