Improvement of Soil Phosphorus Availability by Green Fertilization with Catch Crops

The efficient use of phosphorus (P) is a main task in sustainable agriculture. In pot and field experiments, the effects of green fertilization with catch crops and P supply with organic and inorganic fertilizers on plant and soil parameters were investigated on a P-poor loamy sand. For the field experiment, the catch crops were sown in September and remained on the plots until next spring. As the main crops, oilseed rape (Brassica napus), spring barley (Hordeum vulgare), and spring wheat (Triticum aestivum) were cultivated. The yield and P uptake of the main crops were determined. In the soil, the organic matter content, pH, P in soil solution (Psol), double-lactate and oxalate P content, P sorption capacity, and degree of P saturation were measured. Soil from plots of selected fertilizer treatments of the field experiment [without P, cattle manure, compost, triple-super P, green fertilization with Phacelila (Phacelia tanacetifolia)] was used for the pot experiment. Maize (Zea mays), ryegrass (Lolium westerwoldicum), and buckwheat (Fagopyrum esculentum) were cultivated for 3 months in pots with 6kg soil. All applied forms of fertilizer affected the P contents in soil and the yields and P uptakes of main crops in both experiments. For green fertilization especially, phacelia was found to contribute to the P supply of the main crops, because it increased the P uptake as well as the readily available P contents in soil significantly. The cultivation of ryegrass led to a reduction of the P availability in soil. The DPS was also affected due to the catch crops. In average of the three years of the field experiment the DPS was 47.0% when phacelia was cultivated and 44.5% when ryegrass was cultivated. A better P availability and P utilization by catch cropping can help to reduce the need for external P input.