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Phosphate loss from cracking clay soils - NT1012

Minimal information exists regarding the magnitude and significance of organic manure applications on the transport of phosphorus from agricultural land to watercourses via subsurface flow. The main aims of this study will be to quantify the risk of phosphorus losses following the application of organic manures to drained clay soils and, if appropriate, to identify land management practices likely to reduce these losses. Hydrologically isolated drainage plots will be established on a clay soil at ADAS Boxworth. Each plot (48 x 24 m) will contain 2 subsurface lateral drains 24 m apart which will discharge to a discrete carrier drain. A datalogger will be used to electronically record data and to control automatic water samplers (1 per plot; capable of collecting 24 individual 200 ml samples in 1 cycle) which will collect drain flow samples on a flow proportional basis. Manure treatments applied to plots will be control, inorganic nitrogen, farmyard manure, pig slurry and broiler litter; 2 replicate plots will be used for each treatment, arranged in a randomised block design. Manure treatments will be applied in the autumn each year from 1994 to 1997; these will be ploughed down prior to drilling winter wheat. Annual manure dressings will be analysed to determine the amount of total phosphorus applied and forms of P applied in the manures. Overwinter drainage samples will be collected on a plot by plot basis for each individual drainage event. Based on hydrograph characteristics, selected samples will be analysed for molybdate reactive phosphorus (MRP), total dissolved phosphorus (TDP) and total phosphorus (TP). The volume of drainage water for each plot will be calculated, which, along with drainage water concentrations of MRP, TDP and TP, will be used to calculate phosphorus losses (kg/ha). In addition, composite samples produced by bulking the flow proportional samples (from the first 2 drainage events) will be analysed for dissolved organic carbon (DOC), biological oxygen demand (BOD) and chemical oxygen demand (COD). Soil samples (4 incremental depths) will be taken in autumn 1994 to characterise the site (water soluble phosphorus, NaOH phosphorus, Olsen phosphorus, total phosphorus and physiocochemical parameters such as pH, N, K and Mg) and again at the end of the study to assess effects of the manure treatments on forms of phosphorus present in the soil. Grain yields and grain phosphorus concentrations will be measured annually and crop phosphorus offtakes calculated; these data along with phosphorus loss measurements, will be used to construct the manure treatment phosphorus balances. Results will be used to identify manure management practices that will reduce phosphorus losses from soils.
Time-Scale and Cost
From: 1994

To: 1999

Cost: £328,478
Contractor / Funded Organisations
Fields of Study
Fertilisers and Nitrate Pollution