Development of a Model-based Phosphorus Management Tool for Manure Applications in Subsurface Drained Field

作为畜牧业的副产品，粪肥是作物营养素的宝贵来源（例如，磷、氮和有机物）。加拿大地下排水农田的粪肥生产和处理的三个主要区域是安大略西南部、魁北克东南部和安大略南部。然而，农业土壤和以无机肥料或粪肥的形式施加在其上的营养物是静止水体的主要非点源污染物。此类水体的富营养化与地下排水引起的磷（P）和氮（N）富集有关。实地研究表明，大多数P沥滤到这些水体地下排水流。通过田间试验研究了施用有机肥对地下排水农田土壤中磷的去向和迁移的影响。结合田间试验，基于模型的工具可以帮助理解土壤-植物系统中的P和N循环科学，并促进营养管理，以保护水生环境，同时保持作物产量。然而，P例程在大多数模型中已经看到很少更新，自20世纪80年代中期以来，因此，需要提高P运输的模拟。特别是，许多这些模型假设施用的粪肥立即与表土混合。之所以进行这种简化，是因为在大多数情况下，模型没有确定足够数量的不同有机物库，而且只模拟了数量非常有限的田间管理做法。在大多数情况下，SCS（土壤保持服务，美国）曲线法用于计算地表径流和修订的通用土壤流失方程用于估计泥沙流失。此外，大多数这样的模型既没有地下排水组件，也没有任何能力，物种施加的粪肥。本计划的目标是开发一个P管理工具的根区水质模型（RZWQM 2）的基础上，并使用它来模拟磷的命运和转换在现场尺度。这一新的基于模型的工具，RZWQM 2-P，将在加拿大作为一个决策支持工具，在粪肥应用下的磷管理。该磷氮模型的新功能包括：（i）使用Green-Ampt模型和可变源区预测径流，（ii）使用WEPP的机械子程序模拟沉积物的剥离、沉积和输运过程（水蚀预测项目），（iii）肥料中的磷分配到土壤残留物和土壤腐殖质库中，取决于施用方法（表面施加或注入），（iv）P的吸附/解吸将通过NICA计算（非理想竞争吸附）模型，用Fe/Al/Ca含量预测溶解态磷的吸附/解吸;考虑优先流，将模拟附着在土壤纳米颗粒上的颗粒P从土壤表面到瓷砖排水沟的运输，（v）作物磷素吸收和胁迫子程序将采用DSSAT（农业技术转移决策支持系统）模型。新的基于模型的磷管理工具，RZWQM 2-P，将测试对地下排水作物田在加拿大的磷水平。已在多个地区测量了地表径流和地下排水中的磷，可用于校准和验证新的管理工具。由我的团队在麦吉尔大学麦克唐纳农场进行的一项关于家禽和牛粪下P运动的蒸渗仪研究的数据可以用于新的P模型的参数化。这一新的管理模式可以作为决策支持工具，水质和作物产量管理下粪肥的应用。

A by-product of the livestock industry, manure is a valuable source of crop nutrients (e.g., phosphorus, nitrogen, and organic matter). The three major clusters of manure production and disposal on subsurface drained cropland in Canada are south-western Ontario, south-eastern Quebec, and southern Ontario. However, agricultural soils and the nutrients applied thereon, in the form of either inorganic fertilizers or manures, are the major non-point source pollutants of standing water bodies. Eutrophication of such water bodies has been linked to phosphorus (P) and nitrogen (N) enrichment by subsurface drainage. Field studies have shown that the majority of P leached to these water bodies followed subsurface drainage flow. A number of field experiments have been conducted to investigate the fate and transport of P under manure application in subsurface-drained croplands. In combination with field experiments, model-based tools can help to understand the science of P and N cycles in soil-plant systems and facilitate the management of nutrients to protect aquatic environments while maintaining crop yield. However, P routines in most models have seen little updating since the mid 1980s; therefore, the need arises to improve the simulation of P transport. In particular, a number of these models assume applied manure to be immediately mixed with top soil. This simplification was made because in most cases the models had not defined a sufficient number of different organic matter pools and only a very limited number of field management practices were simulated. In most cases, the SCS (Soil Conservation Service, USA) curve method was used to compute surface runoff and the Revised Universal Soil Loss Equation was employed to estimate sediment loss. Furthermore, the majority of such models have neither a subsurface drainage component, nor any ability to speciate applied manure. The objective of the present program is to develop a P management tool based on the Root Zone Water Quality Model (RZWQM2) and use it to simulate the fate and transformations of P at the field scale. This new model-based tool, RZWQM2-P, will be used in Canada as a decision-support tool for P management under manure applications. The new features of this P and nitrogen model will include: (i) the use of the Green-Ampt model and variable source area to predict runoff, (ii) simulation of sediment detachment, deposition, and transport processes using a mechanical subroutine adopted from WEPP (Water Erosion Prediction Project), (iii) partitioning of P in manure into soil residue and soil humus pools depending on the application method (surface applied or injected) ,(iv) adsorption/desorption of P will be computed by a NICA (non-ideal competitive adsorption) model which uses Fe/Al/Ca content to predict dissolved P adsorption/desorption; transport of particulate P attached to soil nanoparticles from the soil surface to tile drains will be simulated considering preferential flow, and (v) a crop P uptake and stress subroutine will be adopted from the DSSAT (Decision Support System for Agrotechnology Transfer) model. The new model-based P management tool, RZWQM2-P, will be tested against P levels measured on subsurface-drained crop field in Canada. P in surface runoff and subsurface drainage has been measured in several areas and can be used to calibrate and validate the new management tool. Data from an on-going lysimeter study on P movement under poultry and cattle manure, conducted by my team at the Macdonald Farm of McGill University, can serve in parameterizing the new P model. This new management model can be used as a decision-support tool for water quality and crop yield management under manure applications.