Abstract
Copper (Cu) and iron (Fe) are essential micronutrients for plants and animals. How phosphorus (P) application affects Cu and Fe concentrations in maize grain still remains unclear. Two-year field studies were conducted in a long-term experiment with six P levels (0, 12.5, 25, 50, 100, and 200 kg∙ha−1 P) on calcareous soil. Phosphorus application significantly decreased the average grain Cu concentration by 12.6% compared to no P treatment, but had no effect on grain Fe concentration. The copper content increased as the P application rate increased from 0 to 25 or 50 kg·ha−1, but then decreased, while Fe content kept increasing. As the P application rate increased, the specific Cu uptake by the roots decreased, but not for Fe. The root length density in response to P application had a positive relationship with shoot Cu and Fe content. The shoot Cu content and grain Cu concentration decreased with the reduction in the arbuscular mycorrhizal fungi (AMF) colonization of roots due to increasing P application. The reduction in grain Cu concentration with increasing P rates could be partly explained by the decreasing uptake efficiency.
Highlights
Maize is an important ingredient in animal feed and industrial products [1], providing substantial levels of calories and protein [2], and micronutrients such as copper (Cu), iron (Fe), and zinc (Zn) [3,4]
The application of phosphorus (P) fertilizer in intensive agriculture production is a crucial measure for increasing grain yield [9,10], but it may affect the micronutrient contents in grain
Our findings showed that P application significantly decreased the grain Cu concentration by 3.4–23.4%, while an optimal P application (25 kg·ha−1 ) decreased grain Cu concentration by 8.6%, and excess (200 kg·ha−1 ) led to a grain Cu concentration reduction of 23.4%, whereas P application had no effect on grain Fe concentration
Summary
Maize is an important ingredient in animal feed and industrial products [1], providing substantial levels of calories and protein [2], and micronutrients such as copper (Cu), iron (Fe), and zinc (Zn) [3,4]. The improper management of maize crops, results in low contents of micronutrients in grain, such that the grain nutrients in the feed do not meet animal requirements [5]. Exogenous micronutrients must be added to the feed to increase animal body weight [6]. The addition of large amounts of micronutrients, and especially Cu, to the feed can result in substantial soil and water pollution [7,8].
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