Effect of residue mixtures on response of cumulative respiration to salinity

The study aimed to investigate the response of soil respiration to salinity when amended with mixtures of rapidly and slowly decomposable residues. Two incubation experiments were carried out with loam soils having EC(1:5)0.1, 1.0, 2.5 and 3.3 dS m-1. In experiment one, the four soils were amended with 20 g kg-1 soil as sawdust (C/N 114) or kikuyu (C/N 19) alone or mixed at different ratios. In all mixtures, the decrease in cumulative respiration at 1 dS m-1compared to non-saline soil was smaller than with sawdust alone. In experiment two, three soils (EC(1:5)0.1, 1.0 and 2.5 dS m-1) were amended once or three times to a total addition rate of 10 g C kg-l soil either with sawdust alone, kikuyu alone or mixtures. In the treatments with mixtures, the decrease in cumulative respiration from non-saline to EC 1 dS m-1 was smallest in the treatments with three residue additions where 25% kikuyu was added on day 0 or on day 14 after addition of 50% sawdust on day 0. We conclude that even a relatively small proportion of rapidly decomposable residue in a mixture is sufficient to alleviate the negative impact of salinity on soil respiration.