Enriching Rice Grain Zinc through Zinc Fertilization and Water Management

Abstract

Core Ideas Rice grain‐Zn concentration increased with more aerobic soil conditions. Fertilizer‐Zn applied to soil had limited effect on rice grain‐Zn concentration. Rice paddy water management affected soil redox potential and DTPA‐extractable Zn. Combined water and Zn management are useful for agronomic Zn biofortification. Agronomic biofortification was not sufficient to meet rice Zn nutrition targets. Increasing rice (Oryza sativa) grain‐Zn concentration is important for achieving improved human nutrition. Our objective was to understand how agronomic management practices, including water management and fertilizer‐Zn application rate and timing, affect plant growth, grain‐Zn concentration, and yield of rice genotypes. In a series of four‐field experiments over three seasons, we tested multiple combinations of water management techniques and fertilizer‐Zn application techniques. The use of alternate wetting and drying (AWD) water management increased (p < 0.001) soil redox potential and diethylene triamine pentaacetic acid (DTPA)‐extractable soil Zn compared with continuous flooding (CF) in the 0‐ to 2‐cm soil depth, but not always in the 2‐ to 10‐cm depth. On average, AWD grain‐Zn concentration increased 9% over CF without any yield penalty. Fertilizer‐Zn application increased DTPA‐extractable Zn only in the top soil layer and only temporarily, with a corresponding increase in grain‐Zn concentration only at rates > 10 kg Zn ha−1. Different timings of fertilizer‐Zn application (from basal to flowering) had no effect on grain‐Zn concentration or yield. Overall, our results indicated that AWD had a consistent and larger positive effect than fertilizer‐Zn application on grain‐Zn concentration. However, the increase in grain‐Zn concentration due to fertilizer‐Zn or water management was small, up to 2 mg Zn kg−1 brown rice, implying that improved agronomic management alone is not sufficient to meet the target increase of at least 10 mg Zn kg−1, but is a useful complementary strategy for enhancing the performance of Zn‐enriched rice by improving soil‐Zn availability.

Zn uptake behavior of rice genotypes and its implication on grain Zn biofortification

“…3), suggesting the beneficial effect of LSD on grain Zn loading for genotype IR69428. Our results slightly differ from those of Tuyogon et al 10,. who reported that AWD had a positive effect on grain Zn concentration but that the contributed increase was minimal (2.0 μg g −1 ); hence, the desired grain Zn concentration (30.0 μg g −1 ) was not achieved.…”

“…The concentrations of DTPA-extractable Zn under MSD in our pot experiments (0–2 cm soil depth) were up to 8 times higher than the values reported by Tuyogon et al 10. for field experiments at 0–2 cm soil depth under AWD and ZF at 10 kg Zn ha −1 .…”

“…The seed used for experiment 1 was IR69428-6-1-1-3-3 ( Tropical japonica ), a high-grain Zn genotype10 with a relatively long duration (94 days to flowering). In experiment 2, both IR69428-6-1-1-3-3 and IR68144-2B-2-2-3-1-127 (released as variety MS13 in the Philippines in 2003) ( Indica ) were used to represent a contrast between indica and japonica with different genetic heritages.…”

“…who concluded that grain Zn concentration is largely determined by genotype rather than by Zn fertilization, which could be attributed to differences in Zn uptake behavior. In addition, Tuyogon et al 10,. who used both IR68144 and IR69428 in field experiments, observed a significant increase in DTPA-extractable soil Zn and grain Zn uptake in longer-duration genotypes as a result of water management (WM), such as by alternate wetting and drying (AWD).…”

“…Breeding efforts for rice grain Zn biofortication include conducting trials on root Zn uptake and or grain Zn loading performance of various genotypes8910. Root Zn uptake has been associated with the release of organic exudates from rice roots (see review by Rose et al 11…”