Resumen de Addition of residues with different C/N ratio in soil over time individually or as mixes - effect on nutrient availability and microbial biomass depends on amendment rate and frequency
Thi Hoang Ha Truong, Petra Marschner
Residues with different properties may be added to soil simultaneously (as mixes) or after each other. In most previous studies on the effect of mixes on decomposition and nutrient release, residues were added once at the start of the experiment. Less is known about the effect of mixtures added more than once on soil respiration, microbial biomass and nutrient availability and how the addition frequency influences interactions between high C/N (H) and low C/N (L) residues in mixes. In the 48-day incubation experiment with total amendment rate in all treatments was 20 g kg-1, treatments differed in addition frequency (twice, four or eight times), rate (10, 5 or 2.5 g kg-1) as well as order of H and L. Soil was sampled every 12 days. Treatments had similar total cumulative respiration, but differed in distribution over the 12 day periods. Available N and MBN changed strongly over time in treatments with 10 or 5 g kg-1, depending on the C/N ratio of the residue added before sampling. Frequent addition of small amounts of residues (2.5 g kg-1) limited microbial N uptake initially compared to higher amendment rates, but resulted in similar available N irrespective of the C/N ratio of the residue added. It can be concluded that with less frequent residue addition, microbes decompose mainly the recently added residue. With more frequent addition, microbes decompose recently added residue together with residue added before the most recent amendment.
