Abstract
Although application of Zn combined with macronutrients (K, P, and N) can be used to fortify wheat grain with Zn, little is known about their interactions when foliar application is employed or the influences of common soil fertility management practices (e.g. N and straw management) on their efficiency. Therefore, the effects of foliar-applied Zn and N, P, or K on grain nutritional quality (especially Zn) were investigated in wheat grown under different soil N rates at two sites with (Sanyuan) or without (Yangling) employing straw return. A 4-year-long field experiment was also conducted to evaluate the environmental stability of the foliar formulations. Across 6 site-years, foliar Zn application alone or combined with N, P, or K fertilizers resulted in 95.7%, 101%, 67.9% and 121% increases in grain Zn concentration, respectively. In terms of increasing grain Zn concentration, foliar-applied Zn positively interacted with N (at Sanyuan) and K (at Yangling), but negatively interacted with P at any condition tested, suggesting depressive effects of foliarly-applied P on physiological availability of Zn. Although these interaction effects were the major factor that governing the efficiency of foliar-applied Zn combined with N, P, or K on grain Zn concentration, the magnitude of the increase/decrease in grain Zn (–3.96~5.71 mg kg-1) due to these interactions was much less than the average increases following Zn+K (31.3), Zn+P (18.7), and Zn+N (26.5 mg kg-1) treatments relative to that observed in foliar Zn-only treatment. The combined foliar application of Zn with N, P, or K did not cause any adverse impact on grain yield and other nutritional quality and in some cases slightly increased grain yield and macronutrient concentrations. Grain phytic acid:Zn molar ratios were respectively 52.0%, 53.1%, 43.4% and 63.5% lower in the foliar Zn, Zn+N, Zn+P and Zn+K treatments than in the control treatment. These effects were consistent over four years and across three soil N rates. Overall, combined foliar application of Zn with N, P, or K can successfully fortify wheat grain with Zn (above 40 mg kg-1), and including Zn in foliar N or K application are preferred for practically increasing dietary Zn intake.
Highlights
Zinc deficiency in humans is a well-documented problem that can cause impairments in brain function, the immune system, and growth [1]
When averaged across cropping season, foliar Zn application significantly increased the grain Zn concentration by 107% at Yangling and 78.3% at Sanyuan compared with the control treatment (Table 2)
The increase in the grain Zn concentration caused by the Zn+N treatment was similar to that caused by the foliar Zn treatment for all soil N rates at Yangling
Summary
Zinc deficiency in humans is a well-documented problem that can cause impairments in brain function, the immune system, and growth [1]. Increasing Zn concentrations in wheat grain using agricultural tools such as Zn fertilization is receiving increased attention to effectively combat health problems related to Zn deficiency [3, 4]. Zinc fertilization methods include soil and foliar applications, the use of Zn-enriched NPK fertilizers, and seed priming [5, 6]. Numerous studies have demonstrated marked increases in grain Zn concentrations due to foliar Zn spray, whereas soil Zn applications and seed priming are less effective [6, 7, 8]. Org) have emphasized the use of Zn in combination with foliar N, P, and K fertilizers to practically combat Zn deficiency [5]. The current understanding of possible factors affecting the efficiency of these fertilizers is incomplete
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