Effects of genotypes and zinc fertilizer management on grain yield and quality in rice

Abstract

Rice (Oryza sativa L.) is the major staple food and source of energy for more than half of the world’s population, but it is poor in essential micronutrients such as zinc (Zn), compared with the other cereal crops. Low Zn contents in rice grain not only impact human health but also affect plant growth and productivity. Agronomic biofortification by fertilizer application, plant breeding and genetic engineering are suggested as a means to increase the grain Zn content in rice. Agronomical management is practical and effective in farmer’s fields in many countries. However, there is limited information on the effects of rice variety and Zn fertilizer management, especially on those with different original grain Zn concentration and grain quality attributes, and also the confounding effects of yield under the influence of water and fertilizer management. This study aimed to evaluate the effects of genotypes and cultivation management on grain yield and quality in rice, in 4 experiments. The first study evaluated the effect of foliar Zn, applied as 0%, 0.1%, 0.2%, 0.3% and 0.4% ZnSO4.7H2O on two rice cultivars, Chai Nat 1 (CNT1) and Kam Doi Saket (KDK) grown as wetland rice in the field at the Faculty of Agriculture, Chiang Mai University, in 2016 and 2017 on yield, grain Zn and phytate concentrations as well as bioavailability of Zn in the rice grain, as indicated by the molar ratio between phytate:Zn. The effect of foliar Zn on Zn concentration of the unpolished and polished grain was different between the varieties and cropping years. Foliar Zn application did not affect grain yield, foliar Zn with 0.3% ZnSO4 had the highest unpolished grain Zn ranging 35.5 - 37.0 mg kg-1 in both cropping years, but had no effect in CNT1. In the polished grain Zn, increasing foliar Zn application rate at 0.2 - 0.3% ZnSO4 increased Zn concentration in both the varieties, ranging between 11.2% - 20% in CNT1 and 8.3 - 24.1% in KDK, respectively in both years. In addition, the application of 0.3% ZnSO4 decreased phytate concentration in unpolished rice of KDK (by 11.5 - 20.9%), while it was not affected in CNT1 in both cropping years. On the other hand, the phytate concentration in the polished rice in 2016, applied at 0.4% ZnSO4 decreased by 26.2% and 16.2% in KDK and CNT1, respectively while in KDK it was increased at 13.6% in 2017. However, foliar 0.3% ZnSO4 decreased molar ratio between phytate:Zn in the unpolished grain by 26.0 - 37.7% in KDK but it was not observed in CNT1 in both cropping years. Furthermore, foliar 0.1 - 0.4% ZnSO4 in both cropping years decreased polished grain by 32.0 - 38.5% in both varieties. These findings indicated that foliar Zn application improved grain Zn concentration as well as it’s bioavailability. However, the other cultivation management may also effect on grain yield and Zn concentration such as water managements. In the second experiment, effects of water management and method of Zn fertilizer application on grain yield and Zn concentration was investigated in a wetland rice cv. Chai Nat 1 (CNT1) and an upland rice cv. Kam Hom Morchor (KH CMU), grown in two different water regimes of waterlogged and well-drain conditions with three Zn fertilizer managements (nil Zn, soil Zn and foliar Zn). The fertilizer was foliar applied with 0.5% ZnSO4.7H2O and soil Zn application was applied at 50 kg ha-1 as ZnSO4.7H2O. Grain yield was significantly affected by an interaction between rice variety and water condition, not by the Zn fertilizer treatment. In CNT1, the wetland rice grown under well-drained condition was found to have 16.0% lower grain yield lower than when grown in waterlogged soil, while the grain yield of KH CMU was not significantly different between the two water conditions. The concentration of Zn in unpolished rice was not affected by water regime but it was affected by Zn application methods. In CNT1, grain Zn was increased by 19.5% and 32.6% in soil and foliar Zn application, respectively. The interaction effect between water regime and Zn application was found in KH CMU. Applying Zn fertilizer through soil and foliar under waterlogged condition had the highest grain Zn concentration of 40.0 - 42.8 mg kg-1, while the highest grain Zn at 41.4 mg kg-1 was found in foliar Zn application under well-drained condition compared with 29.6 mg kg-1 and 36.1 mg kg-1 in no Zn application of well-drained and waterlogged condition. Therefore, applying Zn fertilizer would be an effective way to improve Zn deficiency in both plant and human but it should be carried under an appropriate management of growing condition such as water regime and rice varieties. In addition, the effect of other fertilizer application in rice cultivation should also be evaluated. The third study examined how N fertilizer affect Zn and N concentrations while having different effects on grain yield, in five rice varieties, Chai Nat 1 (CNT1), RD21, Khao Dawk Mali 105 (KDML105), Khao Pong Krai (KPK) and Nam Roo (NR), which differ in yield potential and original grain Zn concentration. Nitrogen fertilizer was applied to the soil at 50, 100, 150, 200, 250 and 300 kg ha-1, or as foliar N with a solution of urea (NH2CONH2) applied at 0, 0.5, 1.0, 1.5, 2.0 and 2.5% N. Increasing soil N at 150 kg ha-1 increased grain yield in CNT1 and RD21 ranged from 47.7 - 73.5 g pot-1, but increasing N at 300 kg ha-1 decreased grain yield in KPK and NR by 52.9% and 65.8%, respectively compared with N supply 50 kg ha-1. Foliar N application had no effect on the yield of all five varieties which was found at 44.7 - 68.8 g pot-1. Applying soil and foliar Zn had affected on grain Zn concentration. Applying soil N at 100 - 300 kg ha-1 increased grain Zn by 50 - 63% in low grain Zn variety (CNT1 and NR), while in medium grain Zn variety (KDML 105) increased by 35 - 37% and in high grain Zn variety (KPK and NR) increased by 33 - 183%. Applying foliar N with 0.5% - 2.5% were found to increase grain Zn concentration in the low grain Zn varieties by 24 - 67%, increased by 45 -59% in KDML105, and increased by 29 - 68% in the high grain Zn varieties. The results indicated that applying N fertilizer to the soil was more effective on grain Zn than the foliar spray, especially in the low-yielding/high grain Zn varieties. These results suggested that applying N fertilizer is not only effect on grain yield, but also grain Zn and N concentrations depending on rice varieties. The fourth study evaluated the effect of sulfur (S) and Zn fertilization on grain Zn and yield. The Osmancik 97 rice variety was grown in greenhouse condition at Sabanci University, Turkey. Plants were grown under low (0.25 mg Zn kg-1 soil) and adequate (5 mg Zn kg-1 soil) applied as ZnCl2, with a factorial combination of soil S as CaSO4.2H2O (2.5, 10 and 50 mg kg-1) and foliar Zn (with 0.5% ZnSO4.7H2O and without) treatments. Increasing S rates increased grain yield in both soil Zn conditions, which great response in adequate soil Zn than low Zn condition. Grain Zn concentration responded to Zn and S rates differently from grain yield. The highest grain Zn concentration was found at 42 mg kg-1 when applied with 2.5 mg S kg-1 soil in the adequate soil Zn condition. While, increasing S rates under low soil Zn condition did not affect grain Zn concentration. This indicating that the accumulation of grain Zn by S fertilizer is depending on the availability of Zn in the soil, the balance soil Zn and S may be the way to improve grain Zn accumulation. In conclusion, foliar Zn application did not affect grain yield while the different plant types of rice varieties used in this study exhibited variation in grain yield. The modern rice variety had a higher grain yield than the traditional rice variety. Considering the rice varieties grown in different cropping years, it was found that grain Zn concentration in different rice varieties was affected by foliar Zn application rates differently. This indicating that the application rates of Zn fertilizer is an essential factor to improve grain Zn concentration, but the response can vary between cropping years. Cropping year has been largely affected by environmental factors (i.e. precipitation, humidity and sunshine duration). In addition, water management with the original ecotype of wetland variety was affected on grain yield, while it was not found the response to water regime in the upland variety. Moreover, increasing Zn concentrations in unpolished rice of the wetland variety was affected by Zn fertilizer management (soil Zn and foliar Zn applications), but in upland rice was affected by an interaction between water regimes (well-drained and waterlogged conditions) and Zn fertilizer management. On the other hand, grain Zn varieties, but there was little effect of foliar N, depends on in yield potential and original grain Zn concentration. However, grain yield of rice varieties responded differently to soil N fertilizer rates, while foliar N had no effect on yield of all varieties. In addition, the application of S fertilizer effect on plant growth and development of rice differently at different soil Zn conditions which can consequently impact on its grain yield and Zn accumulation. Therefore, the appropriate agronomic management and rice variety is not only improved yield and grain Zn concentration, but it would also enhancing Zn intakes in human diet which would be able to alleviate Zn malnutrition among the world population.