Localized fertilization with P plus N elicits an ammonium-dependent enhancement of maize root growth and nutrient uptake

Localized nutrient supply (especially P plus ammonium) can greatly stimulate root proliferation. Ammonium uptake induces proton release and causes rhizosphere acidification. However, the role of ammonium in improving root proliferation and nutrient uptake in the localized application of P plus ammonium is not fully understood. This study examined the ammonium-dependent effect of localized application of P plus N on enhanced root growth and nutrient uptake. The two-year field experimentation with maize (Zea mays L.) was conducted with localized application of P plus N at different ratios of ammonium to nitrate or as urea, with or without a nitrification-inhibitor in a calcareous soil. Localized supply of P plus ammonium significantly increased root proliferation and shoot dry weight compared with other N forms as nitrate and urea in the calcareous soil, even when the amount of ammonium applied was reduced by 50%. The rhizosphere pH significantly declined at localized nutrient-supplied patches with ammonium addition compared with nitrate and broadcasting treatments. The N and P uptake was enhanced by localized application of P with ammonium but not with nitrate or urea. Significant positive correlation was observed between ammonium proportion in the localized patches and root proliferation or N or P uptake. The results indicate that localized fertilization with P plus N elicits an ammonium-dependent enhancement of maize root growth and nutrient uptake at seedling stage in the calcareous soil, suggesting an essential role for ammonium in stimulating plant growth through intensifying root proliferation and rhizosphere acidification as well as improving N and P nutrition. (C) 2012 Elsevier B.V. All rights reserved.