The aim of this study was to investigate the effectiveness of compost and vermicompost as soil conditioners in alleviating salt‐affected soils and increasing maize productivity. A greenhouse trial, consisting of seven soil amendment treatments in a completely randomized design with three replications, was carried out at Khon Kaen University, Thailand, during the rainy season of 2011. Plant height and total dry matter of maize increased in treatments with compost and vermicompost application when compared with the control (no fertilizer) in two types of soils (saline and nonsaline) during the growing season. Soil pH and electrical conductivity in saturation paste extracts were decreased by compost and vermicompost amendments with or without earthworms when compared with unamended treatments in the saline soil. Compost and vermicompost amendments improved cation exchange capacity, soil organic carbon, total nitrogen and extractable phosphorus in both soils. These amendments also increased exchangeable K+, Ca2+ and Mg2+ while decreasing exchangeable Na+ in the saline soil, which suggested that Ca2+ was exchanged for Na+, exchangeable Na+, then leached out, and soil salinity reduced as a result. Soil microbial activities including microbial C and N and basal soil respiration were improved by the application of compost and vermicompost amendments with or without earthworms when compared with the control in both soils. This experiment showed that the compost and vermicompost were effective in alleviating salinity and improving crop growth. Copyright © 2013 John Wiley & Sons, Ltd.

The influence of residue quality on soil organic C (SOC) retention has been called into question. A field experiment in Northeast Thailand, in which contrasting quality organic residues were applied yearly for 13 yr, was used to determine quantities, locations, and stability of SOC in the soil matrix and identify residue quality parameters affecting SOC stabilization in a tropical sandy‐textured soil. Total organic C (TOC) content was highest in intermediate‐quality tamarind (Tamarindus indica L.) at 3.58 g kg−1 (intermediate N, lignin, and polyphenol contents), followed by groundnut (Arachis hypogaea L.) stover at 2.63 g kg−1 (high N), dipterocarp (Dipterocarpus tuberculatus Roxb.) at 2.63 g kg−1 (low N, high lignin and polyphenols), and rice (Oryza sativa L.) straw at 1.77 g kg−1 (high cellulose). Microaggregates (Mi) (0.053–0.25 mm) stored the highest C content (34–49% of TOC), with tamarind having the highest C content. Carbon in large macroaggregates (>2 mm), small macroaggregates (0.25–2 mm), and free organic matter (>0.053 mm) was significantly positively correlated with C, lignin, and polyphenols. Carbon in microaggregates and fine particles (<0.053 mm) was significantly negatively correlated with C/N ratio. Soil fraction C was negatively correlated with residue cellulose contents. Protected C lost through mineralization in Mi was lower in tamarind (7% Mi‐C) followed by groundnut (9.5%), dipterocarp (17.7%), and rice straw (18.6%). It was significantly positively correlated with cellulose and C/N ratios but negatively correlated with N contents. Possible mechanisms of aggregate formation are based on microbial synthesis of both persistent (humic substances) and transient (polysaccharides) binding agents as influenced by residue quality. The results showed clearly that residue quality plays an important role in SOC accumulation in tropical sandy soils.

The objectives of this study were to investigate decomposition patterns and soil organic matter (SOM) accumulation of incorporated residues (10 Mg ha -1 year -1 ) of different quality, and identify microbiological parameters sensitive to changes in SOM dynamics, in a 13-year-old field experiment on a sandy soil in Northeast Thailand. Mass loss was fastest in groundnut stover (high N), followed by rice straw (high cellulose) and tamarind (intermediate quality), and slowest in dipterocarp (high lignin and polyphenol) following a double exponential pattern. The decomposition rate k 1 (fast pool) was positively correlated with cellulose (r = 0.70*) while k 2 (slow pool) was negatively related to lignin (r = -0.85***) and polyphenol (r = -0.81

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Groundnut as a pre-rice crop is usually harvested 1-2 months before rice transplanting, during which much of legume residue N released could be lost. Our objectives were to investigate the effect of mixing groundnut residues (GN, 5 Mg ha À1 ) with rice straw (RS) in different proportions on: (i) regulating N dynamics, (ii) potential microbial interactions during decomposition, and (iii) associated nitrous oxide and methane emissions at weekly intervals during the lag phase until rice transplanting (i, ii) or harvest (iii). Decomposition was fastest in groundnut residues (64% N lost) with a negative interaction for N loss when mixed 1:1 with rice straw. Adding groundnut residues increased mineral N initially, while added rice straw led to initial microbial N immobilization. Mineral N in mixed residue treatments was significantly greatest at the beginning of rice transplanting. Soil microbial N and apparent efficiency were higher, while absolute and relative microbial C were often lowest in groundnut and mixed treatments. Microbial C:N ratio increased with increasing proportion of added rice straw. N 2 O losses were largest in the groundnut treatment (12.2 mg N 2 O-N m À2 day À1 ) in the first week after residue incorporation and reduced by adding rice straw. N 2 O-N emissions till rice harvest amounted to 0.73 g N 2 O-N m À2 in the groundnut treatment. CH 4 emissions were largest in mixed treatments (e.g. 155.9 g CH 4 m À2 , 1:1 treatment). Mixing residues resulted in a significant interaction in that observed gaseous losses were greater than predicted from a purely additive effect. It appears possible to regulate N dynamics by mixing rice straw with groundnut residues; however, at a trade-off of increased CH 4 emissions.