## 4 Discussion
### The Impacts of Organic Amendments and Crop Rotation on Soil Carbon Storage  
After three years of treatment with organic additions, the soil organic C content in these saline soils had significantly increased. The greatest change in the soil organic C was in treatment FYM + G50, which increased from 8.90 to 22.30 t ha\({}^{-1}\), a 151% increase in soil organic C. The high level of C accumulation suggests that loss of organic matter is reduced in the treatments by the improved soil structure, reduced erosion and reduced dispersion of soil particles due to improved aggregation in the reclaimed soils [94; 95]. The deficiency in organic matter is compensated for by the addition of organic amendments, which remove salt as well as adding the organic matter and nutrients that are necessary for crop growth and improvement of soil structure, stability and aggregation [96; 97; 98]. Organic amendments have been shown to increase soil organic C accumulation by many authors (e.g., [99; 100]). The results obtained here are similar to the results obtained by [PERSON], et al. [101], who reported a 56% increase in soil organic C during the application of farmyard manure at the rate of 10 t ha\({}^{-1}\) in Karnataka, India, while [PERSON] and [PERSON] [102] reported a 55% increase in soil organic C after 3 years of crop cultivation in India after the application of farmyard manure at the rate of 20 t ha\({}^{-1}\) during maize-wheat cropping systems. [PERSON], et al. [103] reported a 26% increase in soil organic C after the application of farmyard manure and inorganic fertilizers in rice and wheat cropping systems in India. The large increase in soil organic C in our experiment was due to the continued application over three years of the recommended doses of synthetic fertilizers, plus harvested crop residue incorporation, in a soil that was previously un-managed and salt affected. The increase in soil organic C stocks in reclaimed/salt-affected soils could be explained by two theories: hierarchal aggregation and macroaggregate turnover [51]. According to the hierarchal aggregation theory, the addition of organic amendments causes small soil particles to form clusters, microaggregates and macroaggregates, which are then bound together through coagulation or cementation. The macroaggregate turnover theory suggests that macroaggregates start to form around the perimeter of added organic amendments, which then fragment and repeatedly reform to stabilize the organic matter by macroaggregation. The addition of organic amendments in our study is likely to have increased the formation of organic soil colloids, which promoted the formation of organo-mineral complexes and lead to the formation of aggregates. Decomposition of the organic amendments also increased the availability of nutrients.  
Simulations of Soil Carbon Sequestration in Freshly Reclaimed Marginally Salt-Affected Soils under Wheat-Maize Cropping System  
Our simulations predicted that the application of organic amendments in freshly reclaimed salt-affected soils would greatly increase the soil organic C stocks over the control. There were differences in the sequestration of soil organic C between treatments, due to differences in the properties of the organic amendment. Significant long-term increases in soil organic C have been observed with the application of organic fertilizers, such as farmyard manure, poultry manure and green manures [103; 104; 105; 106]. Gypsum application improves the physico-chemical condition of the soil (bulk density, aggregation and water holding capacity) by reducing the concentration of Na\({}^{+}\) ions, and improving the potential of the soil to retain organic C [32]. The improved soil properties played a significant role in enhancing the organic C sequestration in the reclaimed soils [107].