Improved assessment of nutrient supply for organic farms using phosphorus as an example

Phosphorus (P) is an essential and limited plant nutrient. It must be used as efficiently as possible. In organic farming, biological nitrogen (N) fixation by legumes is the most important source of nitrogen. P deficiency reduces biological N fixation, N availability, and crop rotation yield levels and threatens production sustainability on organic farms. P balance balances are usually negative on organic market crop farms, and plant available P (PCAL) levels are often suboptimal on longer organic farms. Does a negative P impact balance or a supply level A or B mean that P is in shortage and crop stands are undersupplied? In practice, it is difficult for farmers to assess this information and take the right measures. Using the example of the nutrient phosphorus, on-farm and external possibilities to increase nutrient availability will be investigated and developed. On-farm, plant species with high P mobilization capacity can increase P availability and P efficiency. Recycled P fertilizers provide an off-farm P source, close material cycles regionally, and conserve reservoir supplies. Awareness of the need to use P more efficiently in agriculture and to close P loops regionally is still underdeveloped in some cases. Project objectives and expected benefits: - Improved practitioner assessment of P supply to cropland sites, considering P mobilization potential from stable P pools. - Development of management strategies to improve on-farm P availability: mobilization of P from stable pools on sites with low P availability through catch crops and mixtures. - Improved estimation of P fertilizer effectiveness of different organic fertilizers and P and K mobilization from stable pools based on a long-term experiment. - Information for farmers on the nutrient phosphorus and its management: better assessment of the current phosphorus supply status of the fields; knowledge of which measures on the farm contribute to P mobilization; decision-making basis for management measures to improve one's own phosphorus supply on a field-specific basis. Farmers learn to make targeted use of their own P reserves available in the soil.