Interaction effects between Nitrogen and Zinc Fertilizer Applications on growth, Yield and Zinc Homeostasis in rice

Abstract

Zinc (Zn) is an essential element involved in human metabolism, which can be supplied by an appropriate diet. However, Zn deficiencies are common among rice consumers because of low Zn concentration in rice grain and Zn-rich foods such as animal products are expensive. Enhancing Zn enrichment in rice grains through agronomic biofortification is advocated as an immediate and effective approach to combat Zn malnutrition in humans. A better understanding of the physiological basis of Zn uptake, its translocation, the maintenance of Zn homeostasis, Zn partitioning within and between different plant parts and within rice grain, internal allocation, re-allocation, remobilization, and efficient loading into grain is essential for biofortification of rice, but a complete knowledge of these processes in rice is still lacking. In particular, controlling the homeostasis of Zn in rice plants for high productivity and grain Zn concentration is a challenging task, as it is governed by complex genetic and management factors during plant growth. As soil properties are changed with water management, which is affect Zn solubility and plant availability and should be considered combining Zn fertilizer management in rice. The responses in grain yield and Zn concentration of the wetland and upland rice varieties to Zn fertilizer application and different growing conditions was evaluated. The wetland (Chainat 1; CNT1) and upland (Kum Hom CMU; KH CMU) rice varieties were grown under waterlogged and well-drained soil conditions with or without Zn fertilizer application. Zinc fertilizer (ZnSO4) was applied at 0 and 60 kg/ha in three stages at tillering, booting, and flowering. In the wetland variety, CNT1, grain yield decreased by 18.0% in the well-drained soil compared to the waterlogged conditions, but there was an 8.9% decrease in grain yield in the waterlogged soil compared to the well-drained soil in the upland variety, KH CMU. Applying Zn fertilizer affected yields differently between the varieties, decreasing grain yield by 11.9% in CNT1 while having no effect in KH CMU. For grain Zn concentrations in brown rice, applying Zn fertilizer increased Zn concentration by 16.5 – 23.1% in CNT1 and KH CMU under both water conditions. In the well-drained soil, applying Zn fertilizer increased straw Zn concentration by 51.6% in CNT1 and by 43.4% in KH CMU compared with the waterlogged conditions. These results indicated that the wetland and upland rice varieties responded differently to Zn fertilizer application when grown in different conditions. Applying Zn fertilizer in the appropriate rice variety and growing conditions would help farmers to improve both the desirable grain yield and Zn concentration in rice. The combined fertilizer of N-P-K-Zn applications not only achieved higher and more stable rice yields than conventional, applications of Zn fertilizer or N-P-K fertilizer or control conditions but also substantially improved the Zn concentration in rice grains of wetland and upland rice varieties. The effects of foliar and soil applications of N, P, K and Zn fertilizers on yield and Zn accumulation in the wetland (CNT1) and upland (KH CMU) rice varieties were evaluated. The seven fertilizer treatments of (1) control, (2) foliar Zn, (3) foliar N-P-K, (4) foliar N-P-K-Zn, (5) soil Zn, (6) soil N-P-K, and (7) soil N-P-K-Zn were as 0.5% at the rate of 700 L/ha. Both soil and foliar fertilizer applications were applied at the tillering, booting and flowering stages. At maturity, plants were harvested to determine yield and the samples of brown rice were analyzed for Zn concentration. The result showed that the grain yield of the wetland rice variety was the highest increase up to 63.5% by soil application of N-P-K-Zn when compared with the control. Soil applications of Zn, N-P-K and N-P-K-Zn increased 22.0 – 30.2% grain yield in the upland rice variety which was higher than the control. Foliar Zn application had the highest grain Zn concentration of 26.9 mg/kg in CNT1. In KH CMU, foliar N-P-K-Zn application had the highest grain Zn concentration at 39.8 mg/kg. The result showed a positive correlation between grain yield and straw yield in CNT1 (r = 0.77, P < 0.001), but such a correlation was not found in KH CMU. In addition, there is a significant positive correlation between grain Zn and straw yield in KH CMU (r = 0.46, P < 0.05). This experiment indicated that the wetland and upland rice varieties responded differently to Zn fertilizer management for grain yield and Zn accumulation. Higher yields and Zn grain content in wetland and upland rice varieties can also be achieved through soil applications of N-P-K-Zn fertilizer. The results from this study would be useful for the selection of appropriate fertilizer management for increasing grain yield and Zn accumulation in rice cultivation which would be beneficial for both farmers and consumers Combined N and Zn fertilizers are confirmed to be the best combination among micro and macronutrients in several experiments for improving yield and Zn biofortification. Three experiments were performed to evaluate the effect of N and Zn fertilizer management on seed germination, seedling growth, yield, and grain Zn accumulation in a modern improved rice variety (SPT1). A preliminary laboratory study showed that priming seeds with N0.15Zn+ led to a higher germination rate and growth performance. Seedling Zn concentration increased linearly along with the dry weights of root and coleoptile during germination. A second experiment in the field showed that simultaneously priming seeds with 0.15% urea and 0.07% ZnSO4 (N+Zn+) resulted in the highest coleoptile length and seedling dry weight. The highest seedling Zn concentration was observed when priming seeds with N0Zn+ followed by N+Zn+, but the effect disappeared at the later growth stages. A third experiment in the field demonstrated that the highest grain yield increases were achieved by foliar application of N+Zn0 (28.5%) and N+Zn+ (32.5%) compared with controls (N0Zn0). Grain Zn concentration was the highest under foliar N+Zn+, with a 37.9% increase compared to N0Zn0. This study confirmed that seedling growth performance can be enhanced by initially priming seeds with N and Zn solution, while grain yield and Zn concentration can be improved by foliar application of N and Zn fertilizer. Foliar application of N and Zn at different growth stages affects both grain yield and Zn concentration differently. The effects of foliar N and Zn applied at the flowering and milky stages of brown rice plants with and without soil Zn application was evaluated. A glasshouse pot experiment was conducted using a completely randomized design with four replicates. Soil Zn in the form of ZnSO4 was applied at 0 and 50 kg/ha. Foliar fertilizer of 1% urea along with 0.5% ZnSO4 was applied and assigned as (1) nil foliar N and Zn (N0Zn0), (2) foliar N with nil Zn (N+Zn0), (3) nil foliar N with foliar Zn (N0Zn+), and (4) foliar N and Zn (N+Zn+) at flowering and milky stages. Foliar application of N and Zn increased grain yield and yield components in both soil Zn conditions. Grain Zn concentration in brown rice was the highest when foliar N and Zn were applied under nil soil Zn conditions; however, grain N concentration decreased by 13.1 – 28.5% with foliar application at flowering and 18.8 – 28.5% with application at the milky stage. The grain Zn content was increased by foliar application of N0Zn+ and N+Zn+ at flowering and milky stages. Applying foliar N and Zn at flowering or milky stages tended to increase the grain N content when Zn was applied to the soil, while nil soil Zn decreased the N content by 26.8% at flowering and milky stages under N0Zn+. The results suggest that the milky stage is the most suitable for foliar application of Zn for increasing (i) grain yield and (ii) N and Zn concentrations in brown rice without having a dilution effect. The effectiveness of foliar combination between N+Zn at ten different growth stages on grain yield and Zn concentration rice was examined. The wetland rice variety SPT1 (San Pa Tong 1) was grown under the waterlogged conditions. Foliar N+Zn was applied at totaling 10 different applications: (1) nil N and Zn applied (control), (2) maximum tillering (TIL), (3) panicle initiation (PI), (4) booting (BO), (5) flowering (FLO), (6) panicle initiation + 1 week after flowering (PI+1WAF), (7) 1 week after flowering (1WAF), (8) 2 weeks after flowering (2WAF), (9) 1 + 2 weeks after flowering (1+2WAF), and (10) maximum tillering + panicle initiation + booting + flowering (TIL+PI+BO+FLO). Foliar N and Zn were applied using 1% urea and 0.5% ZnSO4 at the rate of 1,000 L/ha. Foliar N+Zn increased grain yield varied by 20 – 51% among the foliar treatments compared with the control. The largest increase of 65% grain Zn concentration from the control was demonstrated when foliar N+Zn was applied at one + two weeks after the flowering stage. Grain yield was positively correlated to grain Zn concentration in brown rice. This study suggests that the foliar application of the combine N+Zn should be carried after flowering stage to effectively enhance (i) yield and yield component and (ii) grain Zn and N concentrations in rice. Grain Zn accumulation is a function of the plethora of processes governed by genes encoding Zn transporter proteins. Several genes responsible for Zn transport and sequestration have been identified in rice. Characterization of expression of Zn homeostasis-related genes in rice plant tissues and analysis of any correlation between the levels of expression of genes in tissue with grain N and Zn accumulation will help identify the role of candidate genes in Zn uptake, transport and accumulation in rice grains. The grain yield was increased after the foliar application of N+Zn+ at the tillering stage at 62.01% compared to N0Zn0 application. The foliar application with N0Zn+ and N+Zn+ at panicle initiation resulted in a significant increase in the Zn concentration in brown rice by 26.04 and 34.20%, respectively from N0Zn0. Expression of 10 rice genes was analyzed in leaves, stem, node and panicle tissue of indica rice variety at tillering and panicle initiation stages by quantitative RT-PCR analysis. Differential levels of expression were recorded for the 10 candidate genes among the different tissue types and stages. The genes were differentially expressed in response to the different foliar applications of N and Zn fertilizers at different growth stages. Seven days after foliar spraying, we found that the relative genes in the expression of OsZIP3, OsZIP4 and OsZIP9 were the greatest in leaves under the foliar application of N+Zn+ at the tillering stage, resulting in the highest grain yield. At the panicle initiation stage, the gene expression levels of OsZIP4, OsZIP7, OsZIP9, OsHAM2, OsDUR3, OsAAP1, OsGS1;1 and OsFd-GOGAT in node were higher in the N+Zn0 than N0Zn+ and N+Zn+ applications. Rice plants grown under the foliar application of N+Zn+ at the tillering stage increase grain yield and yield components and enhance gene expression of OsZIP3, OsZIP4, OsZIP5, OsZIP9, OsHAM2, OsDUR3 and OsGS1;1. On the other hand, the foliar application of N+Zn+ at the panicle initiation stage increases the expression of OsZIP4, OsZIP9, OsHAM2, OsDUR3 and OsFd-GOGAT genes together with the higher accumulation of grain Zn and N concentrations in rice. In conclusion, water management with a different ecotype of rice varieties had a negative impact on grain yield in both wetland and upland varieties. Zn fertilizer application proved more efficient in waterlogged conditions than in well-drained ones. Rice varieties exhibited varied responses to foliar and soil applications. Soil application was more effective than foliar application in enhancing grain yield in both wetland and upland rice. Concerning grain Zn concentrations, the upland rice variety (KH CMU) displayed a more positive response to Zn, N-P-K, and N-P-K-Zn fertilizer management compared to the wetland rice variety (CNT1). Priming seeds with N+Zn+ solution proved suitable for effectively improving the germination rate and seedling growth in the early stages of both modern and traditional improved rice varieties. Foliar application of N+Zn at different growth stages had varying effects on both grain yield and Zn concentration. Furthermore, foliar application of N+Zn could enhance the gene expression of OsZIPs transporter, urea transporter, heavy metal ATPases, ferredoxin-dependent glutamate synthase and glutamine synthetase. The results from this study would be useful information for rice crop cultivation among farmers to stabilize grain yield and increased grain Zn accumulation for the benefit of consumers.