Trash management after green cane harvesting and its effect on productivity and soil respiration

A long-term trash management experiment is in progress at Cenicanas' experiment station to evaluate the effect of continual retention of cane residues on the soil surface after green cane harvesting. The soil is a Mollisol with medium organic matter content (3.6%), high content of P (42 ppm) and K (0.46 cmol/kg) at the beginning of the study. Three trash loads of residues produced by the crop were evaluated: zero, single and double load of fresh residues were retained or removed from the soil surface of each treatment. To evaluate the nutrient supply from each load of residues, six fertiliser rates of N (0-200), P (0-75) and K (0-90) kg/ha were applied. During the plant crop, all treatments yielded close to 150 t/ha. After the eighth crop cycle, the plots without trash retention and without fertiliser application yielded 80 t/ha. The presence of residues or the application of fertilisers increased cane yield by 30 t/ha, while the combination of residues and the application of fertilisers maximised the yield up to 160 t/ha. In general, the cane yield of the trash loaded treatments tended to increase as the rate of NPK was higher. As an indicator of soil microbial activity and crop metabolism, CO2 fluxes from the soil surface were measured just before harvest of the seventh ratoon and two more times at 75 and 93 days in the eighth ratoon crop. CO2 gas emissions from plots with single and double load of residues were three fold (303 mg/m(2)/h) of the plots without trash retention (115 mg/m(2)/h). The following two CO2 samplings detected lower emission rates but the pattern was similar to the sampling before harvest. From the results obtained up to now, it is concluded that higher fertiliser rates are not enough to compensate for the negative effect of residue removal from cane fields.