Use of Red Clover-Based Green Manure in Leek Cultivation

ABSTRACT

In a field experiment with leek, four forms of green manuring with red clover were compared; direct incorporation, biogas residue, compost and green mulch. The application rates were based on concentrations of nitrogen (N) and carbon (C) in the clover roots and shoots in the direct incorporation treatment, and the N-availability. A practically appropriate mulch application rate was included for the green mulch treatment. A mineral fertilizer treatment and an unfertilized control were also included. The criteria compared were; crop yield, crop yield in relation to area of red clover harvested and N-recovery in crop and soil. No differences in leek yield were observed within the treatments with the same amount of N or C added. Leek yield as a function of red clover area harvested was highest in the treatment with the lowest input of biogas residue. The area of red clover needed to produce the same N dose as in the direct incorporation treatment was 10 and 20% greater in the treatments with biogas residue and mulch, respectively, but 50% greater in the compost treatment. The proportion of N supplied with the manure that was taken up by the leek crop or left in the soil profile was around 20% for direct incorporation and application of biogas residue. The lowest fraction of N recovered (4%) was at the lowest dose of green mulch. The amount of mineral N left in the soil profile was highest in the treatment with the highest input of biogas residue, 105 kg ha⁻¹ compared with between 32 and 53 kg ha⁻¹ in the other treatments.