Continuation of these experiments over a longer time will thus be needed to allow to see any such effects. Although 0 P fertilization reduced the P balance at field level with 102–121 kg P ha -1 over four years, this had no significant (measurable) effect yet on the soil P stocks. Further, English ryegrass, silage maize, celeriac and Chinese cabbage made the largest contribution to P removal. Four consecutive years of 0 P fertilization had no effect on neither the crop yield nor the crop P uptake. At the second site, a comparison was made between an arable/grass and a vegetable crop rotation. At the first site, a comparison was made between a mixed crop rotation with or without the inclusion of a catch crop. On each site, we compared the effect of 0 P fertilization on crop yield, soil P status and SOC level to a business as usual scenario, for two crop rotations. In order to address these questions we set up two 0 P fertilization field trials at sites with a very high initial soil P status (i.e. Moreover, important additional questions arise in any P mining strategy: (i) to what extent will crop performance be affected in high P soils under 0 P fertilization, (ii) which crops reduce soil P stocks most efficiently and (iii) how can soil organic carbon (SOC) levels be maintained when organic fertilizers are no longer applied.
Greenhouse experiments have shown that a rapid reduction of the plant available P pool is attained by reducing the P fertilizer input to zero while cropping, but field trials confirming these findings are rare. In order to cut back these P losses over the long term, soil P stocks need to be drastically reduced. Soil phosphorus (P) leaching is one of the major causes of diffuse P losses towards the environment in north-west Europe.
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