Soil, nutrient, and water managementFoliar nutrition of rice to enhance micronutrient concentration in grains P. Stalin, Thejas Das, D. Muthumanickam, T. Chitdeshwari, and V. Velu Department of Soil Science and Agricultural Chemistry, Tamil Nadu Agricultural University, Coimbatore 641003, Tamil Nadu, India E-mail:
[email protected] Key words: foliar spray, critical growth period, micronutrient content in rice Rice, the staple food crop for more than half of the world’s population, supplies adequate energy in the form of calories and is a good source of thiamine, riboflavin, and niacin (FAO 2003). But it lacks other critical vitamins such as vitamin A, minerals such as iron and zinc, and other micronutrients/amino acids that are essential to human health. Increasing the micronutrient density in rice can help alleviate the global problem of micronutrient malnutrition, especially among urban and rural poor people who have little access to enriched food and diversified diets. Among the strategies considered, agricultural approaches (e.g., plant breeding, fertilizer application) seem to be the most viable and sustainable solution (Welch and Graham 2004, White and Broadley 2005). Application of micronutrient-enriched fertilizers (amount, timing, placement, and form) can be a short-term and complementary strategy to improve the micronutrient density of food crops. In view of this, the present study was undertaken. A field experiment was conducted at the Agricultural Research Station in Bhavanisagar, which is situated in the western zone of Tamil Nadu (11°26′N, 77°8′E; 256 m above mean sea level). The soil was sandy loam, red, and noncalcareous (Irugur, Typic Haplustalf). It was found deficient in DTPA Zn (1.03 mg kg–1) but sufficient in all other micronutrients (Lindsay and Norwell 1978). The experiment used medium-duration rice variety ADT39 (120–125 d), which was planted during the wet season (October 2008 to January 2009) under a rice-rice cropping system. There were 13 treatments in a randomized block design with three replications. These included a control (water spray), foliar application of micronutrients at different concentrations during panicle initiation (PI) and at flowering (FF) (T2–T5), foliar application of the same concentration of micronutrients at different growth stages (active tillering [AT], PI, and FF and their combination), and soil application of micronutrients (T11–T13) (Table 1). 2011 International Rice Research Notes (0117-4185) 1 Soil, nutrient, and water management Table 1. Various treatments used to assess the effects of micronutrient application on yield and micronutrient content of rice grains. Treatment 1 2 3 4 5 6 7 8 Application Water spray 0.10% of CuSO4, ZnSO4, FeSO4, and MnSO4 + 0.010% boric acid + 0.010% sodium molybdate 0.25% of CuSO4, ZnSO4, FeSO4, and MnSO4 + 0.025% boric acid + 0.025% sodium molybdate 0.50% of CuSO4, ZnSO4, FeSO4, and MnSO4 0.50% of CuSO4, ZnSO4, FeSO4, and MnSO4 + 0.050% boric acid + 0.010% sodium molybdate 0.25% of CuSO4, ZnSO4, FeSO4, and MnSO4 + 0.010% boric acid + 0.010% sodium molybdate 0.25% of CuSO4, ZnSO4, FeSO4, and MnSO4 + 0.010% boric acid + 0.010% sodium molybdate 0.25% of CuSO4, ZnSO4, FeSO4, and MnSO4 + 0.010% boric acid + 0.010% sodium molybdate 0.25% of CuSO4, ZnSO4, FeSO4, and MnSO4 + 0.010% boric acid + 0.010% sodium molybdate 0.25% of CuSO4, ZnSO4, FeSO4, and MnSO4 + 0.010% boric acid + 0.010% sodium molybdate TNAU micronutrient mixture (12.5 kg ha–1) State Department micronutrient mixture (12.5 kg ha–1) ZnSO4 (25 kg ha–1) Spray time Panicle initiation + flowering Active tillering Active tillering + panicle initiation Active tillering + panicle initiation + flowering Panicle initiation + flowering Flowering Soil application (basal) 9 10 11 12 13 The recommended fertilizer dose of 150:50:50 kg N, P2O5, and K2O ha–1 (in the form of urea, single superphosphate, and muriate of potash) was applied uniformly to all plots. Full doses of P and K were applied basally and N was given in four equal splits (basal, AT, PI, and FF). At harvest, grain and straw yields (adjusted to 14% moisture content) were recorded in each plot. Plant samples were collected and micronutrient content was estimated using standard procedures. Micronutrient content in processed grain was likewise measured. Table 2 shows that foliar application of 0.5% of CuSO4, ZnSO4, FeSO4, MnSO4 + 0.05% boric acid + 0.010% sodium molybdate at PI and FF (T5) and 0.25% of CuSO4, ZnSO4, FeSO4, MnSO4 + 0.010% boric acid + 0.010% sodium molybdate at AT + PI + FF (T8) increased Zn, Cu, Fe, Mn, and B content in whole grain. This may be due to the direct application of micronutrients at critical growth stages, which helped increase the absorption in the grain during ripening (Srivastava et al 1992, Swamy et al 1990, Sheudzhen 1991, Kalyan Singh et al 2003, Muralidharan and Jose 1995). It is worth noting that both T5 and T8 2011 International Rice Research Notes (0117-4185) 2 Soil, nutrient, and water management recorded significantly higher Zn content in the grain (28.4 and 28.9 mg kg–1, respectively), an increase of 47% and 50% over that of the control. T5 and T8 also had significantly higher Fe content in the grain (239 and 213 mg kg–1, respectively; 47% and 31% of that of the control). This finding is of great significance in terms of alleviating micronutrient malnutrition. Application of the TNAU micronutrient mixture (T11) enhanced Cu, Fe, Mn, and B content in the grain. Micronutrient content (Table 2) was higher in brown rice (hull removed from rough rice) than in milled rice (bran and hull layers removed by milling). Parboiled rice (rough rice soaked in water and exposed to steam, dried, and the husk removed) had more micronutrients than milled rice, indicating a higher retention of micronutrients in parboiled rice, which may be attributed to the solubilization and migration to the center of the grain and their setting during the starch gelatinization process (Heinemann et al 2005). In T5, micronutrient content was maximum in brown rice, parboiled rice, and milled rice, maybe because of the higher micronutrient content in rough rice in that particular treatment. 2011 International Rice Research Notes (0117-4185) 3 Soil, nutrient, and water management Table 2. Effect of micronutrient application on micronutrient content (mg kg–1) of whole grain and processed rice. Treatmenta T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 T13 CD (0.05) aSee Whole grain with husk Zn Cu Fe Mn B 19.3 5.3 162 32 4.8 22.2 6.4 176 39 5.6 24.5 7.5 200 44 6.3 26.2 8.6 222 47 6.0 28.4 9.0 239 50 7.0 21.0 6.2 175 38 5.7 25.0 7.1 184 40 6.1 28.9 8.6 213 45 6.8 24.2 7.2 197 42 6.2 22.3 7.1 187 39 6.2 21.7 6.6 176 37 5.2 20.3 6.5 173 36 5.2 23.0 6.0 165 34 5.1 3.5 1.9 16 5 0.2 Zn 27.1 30.4 33.2 35.1 36.5 27.4 30.5 34.0 32.6 31.5 29.1 29.3 29.5 5.4 Brown rice Cu Fe Mn 5.8 132.0 54.3 6.4 136.0 63.9 6.7 142.0 70.1 6.8 149.0 72.2 7.6 161.0 72.8 6.5 135.0 56.2 6.5 133.0 65.2 7.5 157.0 71.0 6.6 140.0 67.9 6.5 137.0 67.3 6.5 135.0 66.1 6.4 134.0 65.3 6.3 134.0 56.3 0.8 18.7 9.6 B 7.4 7.6 7.7 7.4 8.9 7.5 7.6 7.8 7.6 7.3 7.5 7.5 7.4 0.1 Zn 22.2 24.6 27.8 28.9 30.1 22.2 24.3 29.6 26.9 26.6 25.1 26.2 28.4 3.5 Milled rice Cu Fe Mn 5.3 50.6 25.9 5.7 51.6 30.1 5.7 53.0 33.3 5.8 53.2 33.9 6.5 60.3 35.6 5.5 51.8 26.7 5.6 52.0 28.8 6.3 59.3 34.3 5.7 52.8 32.2 5.6 52.2 30.2 5.6 52.0 28.2 5.5 51.6 28.0 5.5 50.5 28.0 0.6 5.4 3.3 B 6.8 7.0 7.2 6.8 8.3 6.9 7.0 7.2 7.0 6.7 6.9 6.9 6.8 0.3 Zn 31.2 36.3 38.9 39.0 41.1 31.5 35.4 40.2 37.3 36.3 34.0 33.8 34.0 3.9 Parboiled rice Cu Fe Mn 10.9 131.7 58.1 11.5 139.3 70.6 11.6 146.1 74.3 11.6 149.4 74.7 13.3 158.0 76.9 11.0 134.0 70.3 11.4 137.0 70.7 11.7 156.4 76.9 11.6 145.3 72.5 11.4 140.5 71.7 11.5 133.7 65.3 11.4 132.7 64.2 11.4 132.7 63.2 1.1 17.7 6.9 B 7.9 8.1 8.3 8.0 9.4 8.0 8.1 8.3 8.2 7.8 8.0 8.0 8.0 0.3 text for details of the treatments. 2011 International Rice Research Notes (0117-4185) 4 Soil, nutrient, and water management T8 recorded the significantly highest yield (6,228 kg ha–1), the increase being 12.7% above that of the control (see figure). Basal application of ZnSO4 (25 kg ha–1) (T13) and 0.25% of CuSO4, ZnSO4, FeSO4, MnSO4 + 0.010% boric acid + 0.010% sodium molybdate at AT + PI (T7) also increased grain yield to 6,137 and 6,005 kg ha–1, respectively, which is on a par with T8. Further, the supply of different micronutrients such as Zn, Cu, Fe, Mn, and B through foliar spraying resulted in better absorption of these nutrients, thereby helping in the photosynthetic activities and effective translocation to storage organs. These contributed to the increased yield (Datta and Dhiman 2001). Straw yield showed a similar response to micronutrient application (see figure). Effect of micronutrients on rice grain yield We can conclude that there is ample scope to enhance the concentration of micronutrients, especially Zn and Fe, in rice grains through foliar application of micronutrients at critical growth stages (T5 and T8), along with the recommended NPK dose. Yield loss in this case is minimal. Enhancing the micronutrient content in seeds will not only prevent malnutrition problems but will also increase the productivity of micronutrient-poor soils. T5 also increased Zn, Cu, Mn, Fe, and B concentrations in processed grain (brown rice, parboiled rice, and milled rice). Since rice is mostly consumed in the form of milled rice, there is a need to create a demand for brown rice, parboiled rice, and other rice products that have superior nutritional value. 2011 International Rice Research Notes (0117-4185) 5 Soil, nutrient, and water management Acknowledgment The financial support received from the Indian Council of Agricultural Research, New Delhi, under the All-India Coordinated Scheme on Micro and Secondary Nutrients and Pollutant Elements in Soils and Plants is gratefully acknowledged. References Datta M, Dhiman KR. 2001. Yield and response of rice (Oryza sativa) as influenced by methods and sources of micronutrient application. Indian J. Agric. Sci. 71:190-192. FAO 2003. 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Effect of micronutrient-based fertilizers on dry matter production, nutrient uptake and yield potential in rice. J. Maharashtra Agric. Univ. 15:363-365. Welch RM, Graham RD. 2004. Breeding for micronutrients in staple food crops from a human nutrition perspective. J. Exp. Bot. 55:353-364. White PJ, Broadley MR. 2005. Biofortifying crops with essential mineral elements. Trends Plant Sci. 10:586-593. 2011 International Rice Research Notes (0117-4185) 6