EFFECTS OF COMPOST MATURATION AND TIME OF APPLICATION ON THE GROWTH AND NUTRIENT ACCUMULATION BY ORGANIC CABBAGE

Cabbage (B. oleracea var. capitata) response to 0 and 30 t/ha of mature cow and horse manure compost (C1: C/N=16.5) and of composted dairy cattle slurry solid fraction with different maturation periods and C/N ratios (C2: C/N=18.4; C3: C/N=21.8) and, incorporated into the soil one month before planting (B) and at planting (P), was evaluated throughout a randomized block design experiment. At the site, a mineral fertilized cabbage experiment was also carried out, with 180 kg ha^-1 of mineral N. All crops were evaluated 0, 20, 34, 48 and 62 days after planting.
The mineral fertilized cabbage showed increased growth rate compared to the organic crops with a final yield of 79.6 t/ha. The timing of compost application did not significantly affect crop growth, except for C2. Organic cabbage yield with the compost treatment C2B and compost C1 (mean of both application dates) were respectively 49.7 and 51.8 t/ha. Yield of crops grown with C2P and C3 were lower (mean of 36.9 t/ha) compared to C2B and C1 and were not significantly different from unfertilized crops (28.7 t/ha). Dry matter content was lower for mineral fertilized crops (9.2%) than for organic crops (mean 12.2%) and differences between the percentage of crop waste residues of organic (25.6%) and mineral fertilized (29.8%) crops were not statistically significant. The apparent compost N efficiency rate decreased from 13.7 to 11.2 and 9.2%, whereas N immobilization period increased from 37 to 42 and 45 days, respectively for C1, C2 and C3. Consequently, N uptake decreased from 99.7 (C1) to 89.8 (C2) and 79.5 kg/ha (C3). The N recovery rate for the mineral N application in the mineral fertilized cabbage crop was 55.3% (N uptake of 99.5 kg/ha).
This study shows that as the C/N of the composts decreased, the period of N immobilisation decreased and the apparent compost N efficiency rate by the crop increased. Consequently, during the cabbage growing period more mineral N was available from the mineralisation of composts with a lower C/N ratio, as well as for the earlier compost application for the mature compost C2.