Nitrogen Source Preference in Maize at Seedling Stage Is Mainly Dependent on Growth Medium pH
Hao-Qing Zhang | Ren-Fang Shen | Xue-Qiang Zhao
To improve crop nitrogen recovery efficiency (NRE), plants must be supplied with their preferred form of nitrogen (N). However, whether pH affects crop N-form preference remains unclear. Here, we aimed to explore how maize (<i>Zea mays</i> L.) preference for NH<sub>4</sub><sup>+</sup> and NO<sub>3</sub><sup>−</sup> is affected by pH and to determine the critical pH controlling this preference. Maize plants were grown with NH<sub>4</sub><sup>+</sup> or NO<sub>3</sub><sup>−</sup> in different soils (pH 4.32–8.14) and nutrient solutions (pH 4.00–8.00). After harvest, plant dry weights, N content, N uptake, NRE, soil pH, and exchangeable aluminum (Al) were measured. Compared with the effect of NO<sub>3</sub><sup>−</sup>, NH<sub>4</sub><sup>+</sup> decreased maize dry weight, N uptake, and NRE by 28–94% at soil pHs of 4.32 and 4.36 and a solution pH of 4.00, whereas it increased these parameters by 10–88% at soil pHs of 6.52–8.02 and solution pHs of 7.00 and 8.00. NO<sub>3</sub><sup>−</sup> increased soil pH and decreased soil exchangeable Al content at soil pHs of 4.32–6.68. Critical soil and solution pHs for changing plant growth and N uptake preference for NH<sub>4</sub><sup>+</sup> vs. NO<sub>3</sub><sup>−</sup> ranged from 5.08 to 5.40 and from 5.50 to 6.59, respectively. In conclusion, the preference of maize seedling growth and N uptake for NH<sub>4</sub><sup>+</sup> vs. NO<sub>3</sub><sup>−</sup> mainly depends on the pH of the growth medium, and maize seedlings generally prefer NO<sub>3</sub><sup>−</sup> in strongly acid soils but NH<sub>4</sub><sup>+</sup> in neutral to alkaline soils.
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