Quantifying maize root response to nitrogen (N) fertilizer, soil texture, and weather is crucial to understand complex soil-root-plant processes. We performed a 2-year x 4 locations (sand content range: 5–95%) x N treatments (range: 0 to 336 kg N ha⁻¹) field experiment in Iowa, U.S. to (1) determine the response of root traits to N fertilizer, and (2) develop generalized functions to aid understanding and prediction of root mass and root to shoot (R:S) ratio. Deep root samples (0−210 cm, increments of 30 cm) were collected using the soil core approach at early to middle grain fill period and quantified root mass, length, and N and C concentrations. In addition, yield and shoot biomass was measured. Root traits and yield had different responses to N fertilizer input. Root mass was maximized at 168 kg N ha⁻¹; zero and excessive N fertilization decreased root mass by 33 and 17 %, respectively. Nitrogen fertilizer significantly affected root traits only in the top 30 cm soil layer. Soil texture affected root traits in a dry year (root mass was positively associated with silt and clay), but not in a wet year, suggesting that soil moisture overwhelms the effect of texture. The combined data (N rates x locations x years) revealed a negative relationship between R:S ratio and yield. This resulted in a new set of equations (e.g., upper bound R:S = e^{(–1.5 – 0.04*yield)}) that can replace the constant R:S approach used in the literature. Yield, which is commonly measured, integrates the effects of environment, management, and genetic variation; hence the proposed equations can be widely applied. This study provides evidence that different plant traits are maximized at different levels of mineral N nutrition. Results can enhance biophysical models and prediction of R:S ratio.

量化玉米根系对氮肥，土壤质地和天气的反应对于理解复杂的土壤-根系植物过程至关重要。我们在美国爱荷华州进行了为期2年x 4个地点（砂含量范围：5-95％）x N处理（范围：0至336 kg N ha ^-1）的田间试验，以确定（1）根系性状的响应氮肥，以及（2）开发通用功能，以帮助了解和预测根质量和根冠比（R：S）。在灌浆初期至中期，使用土壤核心方法收集深根样品（0-210 cm，增量为30 cm），并定量分析根质量，长度以及氮和碳的浓度。另外，测量了产量和枝条生物量。根系性状和产量对氮肥输入的反应不同。根重最大为168 kg N ha^-1 ; 零氮肥和过量氮肥分别使根质量降低了33％和17％。氮肥仅在土壤最上层30 cm处显着影响根系性状。在干燥的一年中，土壤质地会影响根系性状（根团质量与淤泥和粘土呈正相关），而在潮湿的一年中则不会，这表明土壤水分压倒了质地的影响。组合数据（N比率x位置x年份）显示R：S比率与产量之间呈负相关。这产生了一组新的方程式（例如，上限R：S = e ^{（–1.5 – 0.04 *收益率）}），可以代替文献中使用的恒定R：S方法。通常测量的产量综合了环境，管理和遗传变异的影响；因此，所提出的方程式可以被广泛应用。这项研究提供的证据表明，在不同的矿质氮营养水平下，不同的植物性状得到了最大化。结果可以增强生物物理模型和R：S比的预测。