Optimizing soil nitrogen (N) in babyleaf salad crops for sustainable crop production.

合成氮肥的使用比任何其他农业投入都更能增加粮食产量[1]。然而，肥料氮在作物中的回收率通常很低，作物未吸收或固定的肥料氮可能通过土壤气态氮排放和淋溶而损失（图1）。除了对农民造成的经济损失外，种植系统的氮素损失造成的环境损害也很严重[2]。根据ADHB [Project FV 370 b]的研究结果，幼叶菠菜对肥料氮的利用率只有60%甚至40%，因此本研究旨在减少幼叶菠菜系统中氮素的损失，以提高环境的可持续性（尿素、硝酸盐、铵;图1），在不同的土壤条件下，通过控制与作物需求和土壤条件有关的土壤氮素形式的有效性，有可能减少肥料氮的损失。这种控制可以通过以下方式实现：（i）施肥形式和（分割）时间的操作，或（ii）使用氮循环抑制剂（NCI;图1）或（i）和（ii）的组合。虽然已经进行了广泛的NCI相关研究，以确定谷物中的最佳氮肥使用量，事实上，没有关于在许多方面不同的婴儿叶沙拉系统的信息，（24至60天），这使得许多作物在一个季节内连续种植，对土壤氮素有效性的动态有影响因此，本项目的总体目标是了解婴儿叶菠菜种植系统中的氮循环动态，以通过操纵氮肥形式/时间和NCI添加来支持有效的氮肥施用。研究氮肥配方、氮肥施用时间和NCI添加对以下方面的交互作用：（a）土壤氮循环过程（尿素水解、硝化、反硝化、矿化）及其与氮素损失（如NH3、N2 O和NO3-）的关系。(b)幼叶菠菜作物参数（产量、氮素吸收、叶片NO3-、NCI吸收、外观）.研究土壤氮素有效性的季节动态和土壤氮素对氮素损失的贡献在多大程度上取决于作物轮作和管理措施。评估化学方法通过矿化预测土壤氮供应的价值，为绿叶菠菜施肥推荐提供信息。博士生将设计，建立和管理田间实验（在多塞特郡的TWC农田上），并使用从田间取样的土壤和植物材料进行受控盆栽实验和实验室分析（阅读大学）。如目标中所示，处理将包括以下因素的组合：氮肥配方（例如硝酸铵钙、硝酸铵、尿素）、施用率和时间（例如在钻孔时100%，在钻孔时50%，在第一片真叶时50%）和NCI添加（例如脲酶抑制剂nBPT;硝化抑制剂DCD）。在现场，学生将确定NO3-沥滤（蒸渗仪），NH3挥发（被动穿梭）和N2 O损失（静态箱）。将取样用于土壤矿物氮（目标1a，2），土壤氮循环过程潜力（目标1a，目标3）和作物参数（目标1b）的实验室测定。采用15 N标记肥料，通过同位素比值质谱法测定N_2 O-N、NH_3-N（气体样品）和NO_3- -N（土壤提取物）的15 N：14 N比值，研究土壤N和肥料N对氮素损失和植物吸收的相对贡献（目标2）。将测试可矿化氮及其与化学预测因子（例如有机氮组分）的关系（目标3）。

The use of synthetic N fertilizers has been responsible for increased food production more than any other input to farming [1]. However, the recovery of fertilizer N in crops is frequently low and fertilizer N not taken up by the crop or immobilized can be lost via soil gaseous N emissions and leaching (Fig. 1). Additional to economic loss to the farmer, environmental damage caused by N losses from cropping systems is significant [2]. According to the ADHB [project FV 370b], the recovery of fertilizer N in babyleaf spinach is only 60% or even as low as 40%.Our project is therefore motivated by the aspiration to minimize losses of N in babyleaf spinach systems for increased environmental sustainability.Given that the main N loss pathways initiate from different N forms (urea, nitrate, ammonium; Fig. 1) and under different soil conditions, there exists potential to reduce fertilizer N losses through control of soil N form availability in relation to crop demand and soil conditions. Such control might be achieved via: (i) manipulation of fertilization application form and (split) timing(s), or, (ii) the use of nitrogen cycle inhibitors (NCIs; Fig. 1) or a combination of (i) and (ii). Whilst extensive NCI-related research has been conducted for optimal N use in cereals, there is virtually no information in relation to babyleaf salad systems which differ in many aspects including their short growth cycle (24 to 60 days) which allows a number of crops to be grown in succession within a season with implications for dynamics of soil N availability (and thus fertilizer demand).The overall aim of this project is therefore to understand N cycle dynamics in babyleaf spinach cropping systems to underpin efficient N fertilization through manipulation of N fertilizer form/timing and NCI addition.The research will address the following objectives:1. Examine the interactive effects of N fertilizer formulation, N fertilization timing and NCI addition on: (a) soil N cycle processes (urea hydrolysis, nitrification, denitrification, mineralization) and their relationship with N loss (as NH3, N2O and NO3-).(b) babyleaf spinach crop parameters (yield, N uptake, leaf NO3-, NCI uptake, appearance).2. Examine the extent to which seasonal dynamics of soil N availability and the contribution of soil N to N losses depends on crop rotation and management practices.3. Evaluate the value of chemical methods for prediction of soil nitrogen supply via mineralization to inform babyleaf spinach fertilizer recommendations.The PhD student will design, establish and manage a field experiment (on TWC's farmland in Dorset) and also conduct controlled pot experiments and laboratory analysis (University of Reading) using soil and plant material sampled from the field. As indicated in the objectives, treatments will comprise combinations of the following factors: N fertilizer formulation (e.g. calcium ammonium nitrate, ammonium nitrate, urea), rate and timing (e.g. 100% at drilling, 50% at drilling, 50% at first true leaf) and NCI addition (e.g. urease inhibitor nBPT; nitrification inhibitor DCD). In the field, the student will determine NO3- leaching (lysimeters), NH3 volatilization (passive shuttles) and N2O losses (static chambers). Samples will be taken for lab determination of soil mineral N (objective 1a, 2), soil N cycle process potentials (objective 1a, objective 3) and crop parameters (objective 1b). 15N-labelled fertilizer will be applied in pot experiments to examine the relative contributions of soil N and fertilizer N to N loss and plant uptake with 15N:14N ratios of N2O-N, NH3-N (gas samples) and NO3- -N (soil extracts) determined by isotope ratio mass spectrometry (objective 2). Mineralizable N and its relationship with chemical predictors (e.g. organic nitrogen fractions) will be tested (objective 3).