| Phosphorus (P) is vital to plant growth and it is found in every living plant cell, where it is involved in several key plant functions, including energy transfer, photosynthesis, transformation of sugars and starches, nutrient movement within the plant and transfer of genetic characteristics from one generation to the next. Phytic acid (myo-inositol-1,2,3,4,5,6-hexakisphosphate or Ins P6) is the main form of phosphorus stored in grain. Although nitrogen fertilizer application is important for yield increasing in rice production, its negative effect on accumulation of P and the other nutrient elements has simultaneously attracted increasing attention. Initially, a modified procedure which relies on the precipitation of phytate with ferric iron for phytic acid analysis in rice grains was developed. The main rice cultivars were then subjected to different nitrogen treatments and used to study the effect of N on grain phosphorus (P) accumulation and to explore its physiological foundation. From the findings, a fertilizer application regime that can improve both the yield and quality of rice was proposed. The summarized outline of this study is as follows:1. Six cultivars with contrasting agronomic traits were used, and three years (from2008to2010) of field experiments with seven N treatments and one year (in2010) of pot experiments with five N treatments were conducted to study the effect of N on grain phosphorus (P) and other mineral nutrients(K, Mg, Ca, Na, Fe, Zn, Cu and Mn) accumulation. Grain total P and phytate concentration showed a clearly increasing trend as N rate increased for both field and pot experiments. Fe and Mn increased with increasing N rate, but K, Mg, Zn and Cu showed a decreasing trend as the nitrogen rate increased. Accordingly, the depressing effect of N on grain P concentration on the significance for human nutrition and rice quality were discussed, both harvest index (HI) and phosphorus harvest index (PHI) increased with N rate, but PHI was consistently higher than HI, indicating the larger proportion of phosphorus translocation to grain than that of dry matter by N. Further, ratio of PHI/HI differed significantly among genotypes, but was stable across contrasting N treatment. The harvest indices of eight mineral nutrients were lower than harvest index (HI), indicating that there were enough nutrients deposited in vegetative organs like leaf, sheath and stem. Further more, although N increased the mineral absorption that had a little effect on the improvement of translocation of minerals.2. Wuyujing3and Wuyunjing7were used, and seven panicle N treatments in the field experiment were conducted to study the effect of N on grain yield, phosphorus (P) accumulation and the rice quality. The results indicated that fertilizer application for spikelet promotion significantly increased the number of panicles and grains per spike. The yield, total phosphorus and protein content under HN10-0were higher than the other treatments. Perfect rice rate decreased and rice with green and other undesirable colours increased leading to deterioration of the appearance quality of rice grain, In addition, white-core rice kernel rate and white-belly rice kernel rate decreased with increasing N levels. Perfect rice rate increased with application of spikelet promotion fertilizer treatments and the mineral contents under HN5-5were higher than in other treatments, indicating that the spikelet sustaining fertilizer improved the nutritional quality of rice.3. To investigate the effect of basal and spray fertilizer treatments on the grain phosphorus (P) accumulation, yield and quality parameters of rice, field experiments were conducted with two japonica rice namely, Wuyujing3and Wuyunjing7; and four basal fertilizer treatments of various nitrogen and phosphorus combinations and nine foliar fertilizer treatments. Perfect rice, green rice and others rate increased while white-core rice kernel and white-belly rice kernel rate decreased under combined application of nitrogen and phosphorus. Phytic acid and total phosphorus were increased under foliar fertilizer application, and the content varies with spraying time. The appearance quality and mineral nutrient were improved under LT2and LT3, though the yield decreased slightly. T1and T2were significantly the better time to spray.In general, the mechanism of nitrogen depressing P concentration through elevated P translocation was counteracted by increased biomass production especially grain yield. Earing stage fertilizers and foliar phosphorus fertilizer improved the content of phytic acid and total P, and alleviated negative impacts of nitrogen on the nutrition and appearance quality of rice. |
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