Study On Agronomic Regulation Factors And Their Mechanisms Of Rice Iron And Zinc Biofortification

Iron (Fe) and zinc (Zn) are essential micronutrient for all organisms; they play a significant role in metabolism both for plant and animals. However, Fe and Zn deficiency is wide spread all over the world. Malnutrition of Fe and Zn afflicts billions of people and their development, especially in developing countries. A major etiologic factor is the low concentration of Fe and Zn from diets based on the staple cereals.In recent decades, because of the growing increase in population in China and other countries, demand for rice is expected to keep increasing. Rice consumes about90%of total irrigation water and is the largest irrigated crop in the world with low water use efficiency. Since fresh water is becoming increasingly scarce, water-saving rice cultivation must be sought to increase the development of sustainable agriculture.Agronomic regulation factors such as variety selection, foliar fertilizers, cultivation methods, N fertilizer amounts, N fertilizer forms and rice straw incorporation could affect Fe and Zn accumulation. In those potential approaches discussed and possessed to increase Fe and Zn concentrations of rice grains, the fertilizations via foliar applications could still be a sustainable, low cost-effective and high efficient strategy. Until now, most of foliar Fe and Zn applications were used on common rice cultivars and genotypes, few studies were conducted on iron-rich cultivars.Compared with conventional flooded rice cultivation, plastic film mulching cultivation under non-flooded condition (PFMC) arose and prevails in China. Many reports said that PFMC had a striking efficiency in maintenance of soil moisture, increase of soil temperature in the early season and improvement of nutrient transformations and availability. Water use efficiency, rice grain yield, rice quality such as protein and amino acids concentrations were significantly improved. Part of reports proved that PFMC had some negative effect on rice cooking and eating quality. The results were not the same. There were a few reports on rice Fe and Zn nutrition with PFMC. Study on PFMC and its effects on rice quality will make big influence. So in this paper, the development of a new high efficient Fe and Zn foliar fertilizer and its role on Fe and Zn biofortification in rice grains were discussed. On the other hand, we studied the effects of PFMC on rice Fe and Zn accumulations; including various N fertilizers rates, different N fertilizer forms and rice straw incorporation under PFMC. The main results are summarized as follows:(1) Foliar applications of Fe-AA significantly improved Fe concentrations in Fe-rich rice cultivars; a1%nicotianamine (NA) was added to Fe-AA (FeNAl), Fe and Zn in brown rice were greatly enhanced. Compared to the control (CK), average Fe concentration was increased by9.1%and37.9%under Fe-AA and/or FeNAl, respectively. Compared to Fe-AA, Fe and Zn were significantly improved by26.4%and10.6%with FeNAl, respectively.(2) A0.5%ZnSO4·7H2O (FeZnl) was added to Fe-AA, a significant improvement was observed on rice Fe, Zn, protein and amino acids concentrations with four Fe-rich cultivars. Compared to the control (CK), average Fe, Zn, protein and amino acids concentrations of the four cultivars were increased by42.4%,77.6%,6.9%and7.1%separately under treatment FeZnl. Compared to Fe-AA, Fe and Zn were significantly improved by30.6%and55.1%with FeZnl, respectively.(3) Under PFMC, when nitrogen fertilizer rates less than135kg ha-1, rice grain yield as well as protein and amino acids concentrations in polished rice increased with increasing nitrogen fertilizer rates. Rice straw incorporation significantly improved rice grain yield, Fe and Zn concentrations in brown rice; soil qualities were also enhanced. Compared with treatment with rice straw incorporation (M2) to treatment without rice straw incorporation (M1) from2008to2010, average Fe was improved by6.6%,5.1%and5.2%; average Zn was improved by9.4%,7.9%and7.3%; average soil organic matter amount was improved by6.4%,7.6%and12.2%; average soil NH4OAc-extractable K was improved by28.2%,64.0%and52.9%. Amylose content (AC) was slightly affected by N fertilizer rates and rice straw incorporation; gel consistency (GC) and alkali spreading value (ASV) in polished rice had a decrease tendency with increasing N fertilizer rates and rice straw incorporation. GC decrease made rice soft which was good for eating. (4) Plastic film mulching cultivation (PFMC) under non-flooded condition has been considered as a new water-saving technique in rice production, while yield decline from continuous cropping of aerobic rice is a constraint to the widespread adoption of PFMC. Rice straw incorporation has been proposed to counter this negative effect in recent decades. This study examined the effects of three cultivation methods and rice straw incorporation on rice grain yield and quality using "Liangyoupeijiu"(an indica hybrid cultivar). The three cultivation treatments were: conventional flooding cultivation (CFC); non-flooded plastic film mulching cultivation (PFMC); no mulching cultivation in non-flooded condition (NMC). Compared with that under CFC, average rice grain yield under PFMC from2008to2010was significantly improved by8.0%, while total amino acids content was decreased by3.5%, no obvious effect was observed on rice protein, Fe and Zn concentrations in rice; under NMC, the reduction in yield, protein, total amino acids and Fe concentrations were5.1%,4.4%,9.3%and11.8%respectively. With rice straw incorporation, grain yield was improved by113.6kg ha-1,142.6kg ha-1and522.1kg ha-1under CFC, NMC and PFMC respectively. Average rice grain yield, Fe and Zn contents in brown rice were significantly improved by3.3%,3.1%and6.4%with rice straw incorporation. The results of the three years showed the same trend in rice grain yield and nutrition quality. The results indicated that PFMC could improve not only grain yield, but also part of rice nutrition quality. Rice straw incorporation could significantly improved rice grain yield as well as Fe and Zn concentrations in brown rice, which would be a good method to overcome grain yield decline under long term PFMC.(5) In order to assess changes of rice iron (Fe) and zinc (Zn) as affected by polyester resin coated urea (PCU) under conventional flooding cultivation (CFC) and plastic film mulching cultivation (PFMC), a three year field experiment was conducted in Central Zhejiang Province, E China, from2008to2010. Compared with treatment under CFC and/or PFMC, the annual and mean Fe under PFMC in brown rice was improved by9.3%,9.0%and16.2%; Zn was improved by21.8%,16.9%and12.9%, respectively, from2008to2010. Compared treatment applied PCU to treatment using prilled urea (PU), annual and average grain yield was improved by2.9%,8.4%and9.6%; the annual and mean Fe under PCU was improved by7.3%,10.1%and17.9%; Zn was improved by14.8%,11.3%and8.1%, respectively, from2008to2010. Rice production was greatly enhanced by PCU under PFMC and/or CFC. Treatment with PCU had a positive effect on soil alkali-hydrolyzable N compared to treatment with PU. Soil organic matter with PCU was a little lower than that under PU. Different fertilizer types have no obvious effect on soil Olsen P. Non-flooded PFMC made soil organic matter, soil N and K decreased compared to CFC, which suggested that long term PFMC will make soil quality maintenance difficult.(6) Our study proved that controlled release fertilizer (CRF) significantly improved rice production as well as Fe and Zn concentrations in brown rice under CFC and/or PFMC, however, the mechanism was still unknown. A pot experiment was conducted to examine the release rates of CRF within the release period; the results showed that CRF could significantly improve rice dry matter weight, plant N uptake amount. CRF provides better nitrogen nutrition in rice growing period could be some explanation for rice production as well as Fe and Zn concentrations improvement.