Grassland and phosphorous flows - mobilisation by growth

Background and Objective

Phosphorus is an essential element for plant growth. Worldwide phosphorous stocks are limited. Organic farming renounces to use fertilisers containing immediately plant available phosphorous. Since in Middle Europe soils are over fertilized with phosphorous from the 1950^th organic farming scarcely suffers acute deficiency situations in plant production up to know. Mechanisms of phosphorous mobilization from the soils are well known. But without suitable fertilizers measures to improve phosphorus supply from declining soil reserves for phases of high plant demand are rare. The mobilisation of phosphorous from grassland soils and its distribution on other farmland shall be quantified based on a practical example. The biological activity of the soils shall be described by chemical soil indicators. A comprehensive view on development of different phosphorous fractions bound in soils under long year of organic management will be done. Scenarios for the practical use of phosphorous mobilisation shall be derived. Calculating the inner Phosphorus flows of an organic dairy farm provides the opportunity to find appropriate ways to improve nutrient utilization. Also to visualize the extraction of phosphorus from the system helps to place more relevance on this topic.

Approach

Phosphorous flows are modelled based on detailed records of the practical farm work of the research farm of the institute. Additionally, phosphorous uptake of grassland and related mass flows are exemplarily determined in the field for one year. To characterize development of the soil parameters conserved and actual samples of the Trenthorst long term monitoring trial are used.

Results

Due to permanent plant cover grassland soils have high biological activity. This has positive effects on phosphorous uptake compared to annual crops. During grazing phosphorous is circulating in pastures. Only by with cutting and stable feeding phosphorous is transferred to cropland via manures. Also annual forage crops phosphorous uptake can be high. The P export is obviously supplied by the soil Phosphorus reserves.