Measuring plant available phosphorus to increase crop yields and minimise nutrient leaching

磷是植物的一种重要营养物质，需要作为肥料添加，以促进农作物的高效和经济生产。没有一般的土壤试验可以可靠地预测应该添加多少肥料才能使作物生长最佳。如果添加太多，成本会很高，磷酸盐会泄漏到湖泊和河流中，造成严重的污染问题，即富营养化。如果添加量太少，作物产量就会很低，而且不经济。由于世界可用磷储量有限，情况十分危急。石灰化土壤通常通过提高植物的养分利用率而对酸性土壤有益，但石灰化土壤可能会锁住部分磷酸盐，使其无法被植物利用，从而使磷酸盐问题进一步复杂化。一种叫做DGT的新分析技术，模拟了土壤中磷与植物相互作用的方式，提供了一个很好的预测，即为了使植物生长最佳，应该添加多少磷肥。在DGT装置放置在土壤中的过程中，DGT积累的磷直到现在都是在实验室中使用传统程序测量的，但是一种新的手持式XRF设备可以提供即时读数。该项目将首先确定DGT与便携式XRF分析可以用于测量土壤中可供植物使用的磷。它将把新的测量方法与现有的化学测试方法进行比较，并研究它在预测在一系列土壤中生长的两种作物（芸苔作物和豆科作物）的肥料需求方面的效果如何。在对土壤进行石灰处理的一系列实验中，新方法将用于进一步了解石灰处理如何影响植物对磷的有效性，以及石灰处理如何可能影响磷向水体的释放（由于作物根系区淋滤）。这项工作将为施用磷肥和石灰的战略提供信息，并为向农民提供相当迅速和更重要的是可靠的评估肥料需求的工具提供基础。这项工作的结果将为农民带来明显的经济利益。减少从农业土壤中流入水道的磷的损失所产生的环境效益将使一般公众和与环境有关的政府机构受益，在某些情况下，通过限制从饮用水中去除磷的成本，也将使供水公司受益。

Phosphorus is a key nutrient for plants and needs to be added as fertiliser to facilitate efficient and economic production of agricultural crops. There is no general soil test which can reliably predict how much fertiliser should be added for optimal crop growth. If too much is added it is costly and phosphate can leak into lakes and rivers, causing severe pollution problems known as eutrophication. If too little is added crop yields are poor and uneconomic. The situation is critical because world reserves of usable phosphorus are limited. Liming soils, which generally benefits acidic soils by improving nutrient availability to plants may further complicate the phosphate problem by locking up part of the phosphate so that it cannot be used by plants. A new analytical technique called DGT, which mimics the way that phosphorus in the soil interacts with the plant, provides a good prediction of how much phosphate fertiliser should be added for optimal plant growth. The phosphorus accumulated by DGT during the placement of the DGT device in the soil has until now been measured in the laboratory using conventional procedures, but a new handheld XRF device that can provide an instant readout has become available. This project will first establish that DGT with analysis by portable XRF can used to measure the phosphorus in soils that is available to plants. It will compare the new measurement with established chemical tests and investigate how well it can be used to predict fertiliser requirements for two crop types (a brassica crop and a legume) grown in a range of soils. In a set of experiments where soils are limed, the new method will be used to advance understanding of how liming affects phosphorus availability to plants and of how liming is likely to affect the release of phosphorus to water bodies (due to leaching from the crop rootzone). This work will inform strategies for applying phosphate fertiliser and lime and provide a basis for providing farmers with a fairly rapid and, more importantly, reliable tool for assessing fertiliser requirements. The outcome of the work will provide clear economic benefits to farmers. Environmental gains stemming from reduced loss of phosphorus from agricultural soils into watercourses will benefit the general public and government agencies concerned with the environment, and in some cases water companies by limiting the costs of removing P from drinking water.