Carbon storages lime concretion black soils as affected by straw incorporation and fertilization

The effects of a combination of returned straw and different N fertilizer application rates on soil bulk density, organic matter fractions, carbon management index(CPMI) and soil carbon storage of lime concretion black soil were systematically studied, and analyzing the correlations between soil bulk density and organic matter fractions, based on data from a four year experiment using a winter wheat-summer maize rotation system in Mengcheng City, Anhui Province, China. The results showed that the bulk density of surface soil under areas where straw was either incorporated or removed were 1.14~1.20 g·cm-3 and 1.24~1.31 g·cm-3, respectively. Straw incorporation significantly decreased soil density by 2.50%~9.20%, while soil organic matter(SOM) and labile organic matter(LOM) increased over the four years by 2.38%~10.61%(p0.05) and 9.10%~44.74%(p0.05), respectively, after the return of the straw, especially with N fertilizer application rates of 450 and 540 kg N·hm-2.The carbon management index of top soil under the returned straw treatment areas was significantly increased by from2.42% to 87.68%(p0.05) greater than that of the areas where straw was removed when nitrogen fertilizer application was the same, especially with N fertilizer application rates of N 540 kg ·hm-2 compared to area where no fertilizer was N applied. Under the straw incorporation conditions, combination and different N fertilizer application rates increased in CPMI by 41.71%、38.17%、74.62%、48.84% and 48.86%(p0.05) comparison with no nitrogen fertilizer application. The highest CPMI was discovered with treatment S+N3 of nitrogen application rate, compared to S+N1(S+N 360 kg·hm-2), S+N2(S+N 450 kg·hm-2), S+N4(S+N 630 kg·hm-2) and S+N5(S+N 720 kg·hm-2), increased by 23.22%、26.38%、17.33% and 17.31%(p0.05), respectively. CPMI of all treatments of combination of returned straw and different nitrogen fertilizer application rates increased by 2.42%、45.14%、41.51%、78.85%、52.44% and 52.46%(p0.01) than that of R+N0 treatment, however, for areas where straw was removed, CPMI had no significant difference among treatments. The change law of soil carbon storage was consistent with variation of CPMI, according to method for the equal soil quality accumulation, showing a significant difference between areas where straw was incorporated or removed, under the returned straw treatment areas, with N fertilizer application rates treatments were significantly increased by 10.29%~16.35% greater than that of the areas where no fertilizer was added, especially with N application rates of 630 and 720 kg N·hm-2, whilst the same parameters ranged from 25.99%~32.91%, compared to the areas where straw was removed and no fertilizer applied. The relationship analysis showed that SOM and LOM were significantly increased along with decrease in soil bulk density, and relationship coefficient were 0.5540(p0.05) and 0.7575(p0.01), respectively. The analysis indicated that incorporated straw has remarkable function on the aspects of decreasing soil bulk density, and increasing TOM, LOM, CPMI and carbon storage, especially with N fertilizer application rates of middle and high fertilizer levels.