Abstract Plant-based indicators may have the potential to improve fertilizer phosphorus (P) recommendations for maize (Zea mays L.). Our objectives were (i) to validate existing models of critical P concentration (Pc) in maize shoot biomass during vegetative growth and (ii) to evaluate on farm the ability of the P nutrition index (PNI), a plant-based indicator derived from Pc, to predict a positive response to P fertilization. Existing models of Pc for maize were validated in a 3-yr experiment in which mineral fertilizer P was band-applied at planting at four rates (0, 10, 20, and 40 kg P ha−1) on a clay soil with a low to medium-low available-P content based on the soil P saturation index (PM-III/AlM-III). Fertilizer P generally did not affect shoot growth from the V6 to VT stages and grain yield, indicating that nonlimiting P conditions were achieved with no applied P. Critical P concentration under those nonlimiting P conditions was described by a linear function of shoot N concentration (Pc = 0.82 + 0.097 × N, R2 = 0.90), which was close to that previously reported in the same region (Pc = 1.00 + 0.094 × N). The on-farm PNI evaluation was conducted on eight farm sites varying in soil PM-III/AlM-III (0.021−0.308). Five P rates (0, 4.5, 9.0, 17.5, and 35.0 kg P ha−1) were applied on fields where the PNI had been measured the year before. The PNI at the V12 stage measured the year before was a better predictor of the relative grain yield with no P applied than the soil PM-III/AlM-III measured prior to planting. A critical PNI value of 0.9 was established below which a positive response to P fertilization is expected. This plant-based diagnostic approach therefore appears to be a valuable alternative or a complement to the currently used soil P test to decide whether fertilizer P is needed or not for maize production.

中文翻译：

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玉米中临界磷浓度的验证和使用

摘要 基于植物的指标可能具有改善玉米 (Zea mays L.) 肥料磷 (P) 建议的潜力。我们的目标是 (i) 验证营养生长期间玉米芽生物量中临界 P 浓度 (Pc) 的现有模型和 (ii) 在农场评估 P 营养指数 (PNI) 的能力，PNI 是一种基于植物的指标，来自Pc，预测对磷肥的积极反应。现有的玉米 Pc 模型在一项为期 3 年的实验中得到验证，其中矿物肥料 P 在种植时以四种比率（0、10、20 和 40 kg P ha-1）带状施用在低密度粘土土壤上。基于土壤磷饱和指数 (PM-III/AlM-III) 的中低有效磷含量。肥料P一般不影响从V6到VT阶段的枝条生长和籽粒产量，表明在不施磷的情况下实现了非限制性 P 条件。 在那些非限制性 P 条件下的临界 P 浓度由芽 N 浓度的线性函数（Pc = 0.82 + 0.097 × N，R2 = 0.90）描述，这与之前的接近在同一地区报告（Pc = 1.00 + 0.094 × N）。农场内 PNI 评估在土壤 PM-III/AlM-III (0.021-0.308) 不同的八个农场地点进行。前一年测量了 PNI 的田地应用了五种 P 比率（0、4.5、9.0、17.5 和 35.0 kg P ha-1）。前一年测得的 V12 阶段的 PNI 比种植前测得的土壤 PM-III/AlM-III 更能预测未施磷的相对谷物产量。确定了 0.9 的临界 PNI 值，低于该值预期对施磷的积极反应。