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

使用合成氮肥对粮食增产的贡献超过任何其他农业投入。然而，作物的氮肥回收率往往很低，未被作物吸收或固定的氮肥可能通过土壤气态氮排放和淋溶而损失（图1）。除了给农民造成经济损失外，种植系统的氮素损失造成的环境破坏也很严重。根据ADHB [FV 370b项目]，婴儿叶菠菜中肥料N的回收率仅为60%，甚至低至40%。因此，我们的项目的动机是尽量减少婴儿叶菠菜系统中氮的损失，以增加环境的可持续性。考虑到主要的氮素损失途径源自不同的氮素形态（尿素、硝酸盐、铵态氮；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相关的土壤氮素形态有效性，有可能减少肥料氮素损失。这种控制可以通过以下方式实现：(i)操纵施肥形式和（分裂）时间(s)，或（ii）使用氮循环抑制剂（NCIs；图1）或(i)和（ii）的组合。虽然已经对谷物的最佳氮素利用进行了广泛的nci相关研究，但实际上没有关于婴儿叶沙拉系统的信息，这些系统在许多方面都有所不同，包括它们的生长周期短（24至60天），这使得许多作物可以在一个季节内连续种植，这对土壤氮素有效性的动态影响（从而影响肥料需求）。因此，该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，通过操纵氮肥形式/时间和NCI添加来支持有效的氮肥施用。研究将涉及以下目标：1。研究氮肥配方、施氮时间和NCI添加对土壤N循环过程（尿素水解、硝化、反硝化、矿化）及其与N损失（如NH3、N2O和NO3-）的相互作用。(b)婴儿叶菠菜作物参数（产量、氮吸收、叶片NO3-、NCI吸收、外观）考察土壤氮有效性的季节动态以及土壤氮对氮损失的贡献在多大程度上取决于作物轮作和管理实践。评价化学方法通过矿化预测土壤氮供应的价值，为婴儿叶菠菜肥料建议提供信息。该博士生将设计、建立和管理一个田间实验（在多塞特郡TWC的农田上），并使用从田间取样的土壤和植物材料进行对照盆栽实验和实验室分析（雷丁大学）。如目标所示，处理将包括以下因素的组合：氮肥配方（如硝酸铵钙、硝酸铵、尿素）、比率和时间（如钻孔100%、钻孔50%、初真叶50%）和NCI添加（如脲酶抑制剂nBPT、硝化抑制剂DCD）。在现场，学生将确定NO3浸出（溶渗仪），NH3挥发（被动穿梭）和N2O损失（静态室）。样品将用于实验室测定土壤矿物氮（目标1a， 2），土壤氮循环过程电位（目标1a，目标3）和作物参数（目标1b）。利用同位素比质谱法测定N2O-N、NH3-N（气体样品）和NO3- N（土壤提取物）的15N:14N比率（目的2），在盆栽试验中施用15N标记肥料，研究土壤N和肥料N对N损失和植物吸收的相对贡献。将测试可矿化N及其与化学预测因子（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).