In semiarid sandy soil environments there is a dual challenge of carbon and nitrogen (N) limitation that needs to be managed to ensure timely supply of N to crops. Management of N inputs to soil using combinations of legume stubble addition and fertiliser N in cereal systems is essential to meet crop demand and maintain N in soil organic matter. The aim of this study was to assess soil mineral and biological N pools that influence N supply and N uptake of wheat at early growth stages. The recovery of 15N-labelled fertiliser by wheat was evaluated using a factorial combination of either wheat, lupin or no stubble incorporated with or without 15N fertiliser in a sandy soil system. Soil and plant samples were collected at sowing, tillering, first node and booting to monitor changes in N pools and 15N uptake by the wheat. Crop stubble incorporation one week before sowing increased biological N pools in the surface soil (0–10 cm). Early N immobilisation (sowing–tillering) in all the treatments without 15N fertiliser may have limited N availability for wheat uptake in the subsequent period (tillering–first node), when fertiliser N appeared critical to maximise N supply for plant requirements. Up to 38% of the 15N fertiliser applied at sowing was incorporated into the soil microbial biomass pool, so that fertiliser N was critical to relieve short-term inherent N limitations for both plant and microbial growth, and to supply the longer-term biological pools (microbial biomass) to support subsequent mineralisation potential. Reducing the energy limitation to the microbial pool through inputs of carbon from stubble was also critical to ensure fertiliser N supplied sufficient N to satisfy plant demand later in the growing period. These results have implications for management decisions on semiarid sandy soil systems that aim to synchronise N from inputs of legume stubbles and fertiliser with crop N demand during early growth stages of wheat.

中文翻译：

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早期生长季节固定影响沙质土壤中分蘖后小麦从作物茬和 15N 肥料中吸收氮

在半干旱的沙质土壤环境中，存在碳和氮 (N) 限制的双重挑战，需要对其进行管理以确保及时向作物供应氮。在谷物系统中使用豆科作物残茬添加和肥料 N 的组合来管理土壤的 N 输入对于满足作物需求和保持土壤有机质中的 N 至关重要。本研究的目的是评估影响小麦生长早期氮供应和氮吸收的土壤矿物质和生物氮库。使用小麦、羽扇豆或无茬在沙质土壤系统中掺入或不掺入 15N 肥料的因子组合来评估小麦对 15N 标记肥料的回收率。在播种、分蘖、第一个节点和启动时收集土壤和植物样品，以监测小麦氮库和 15N 吸收的变化。播种前一周加入作物茬增加了表层土壤（0-10 厘米）中的生物氮库。在没有 15N 肥料的所有处理中，早期氮固定（播种 - 分蘖）可能会限制随后时期（分蘖 - 第一个节点）小麦吸收的氮可用量，此时氮肥似乎对于最大限度地满足植物需求的氮供应至关重要。播种时施用的 15N 肥料中多达 38% 被纳入土壤微生物生物量库，因此肥料 N 对于缓解植物和微生物生长的短期固有 N 限制并提供长期生物池至关重要（微生物生物量）以支持后续的矿化潜力。通过从秸秆中输入碳来减少对微生物库的能量限制对于确保肥料 N 提供足够的 N 以满足植物生长后期的需求也至关重要。这些结果对半干旱沙质土壤系统的管理决策具有影响，旨在使豆科植物残茬和肥料输入中的氮与小麦早期生长阶段的作物氮需求同步。