The effect of maize straw placement on mineralization of C and N in soil particle size fractions

Abstract

Summary Fundamental knowledge about the complex processes during the decomposition, mineralization and transfer of residue organic matter in soils is essential to assess risks of changes in agricultural practices. In a double tracer (13C, 15N) experiment the effect of maize straw on the mineralization dynamics and on the distribution of maize‐derived organic matter within particle size fractions was investigated. Maize straw (a C4 plant) labelled with 15N was added to soils (13.2 g dry matter kg–1 soil) which previously had grown only C3 plants, establishing two treatments: (i) soil mixed with maize straw (mixed), and (ii) soil with maize straw applied on the surface (surface). Samples were incubated in the laboratory at 14°C for 365 days. The size fractions (> 200 μm, 200–63 μm, 63–2 μm, 2–0.1 μm and < 0.1 μm), obtained after low‐energy sonication (0.2 kJ g–1), were separated by a combination of wet‐sieving and centrifuging. The mineralization of maize C was similar in the two treatments after one year. However, decomposition of maize particulate organic matter (predominantly in the fraction > 200 μm) was significantly greater in the mixed treatment, and more C derived from the maize was associated with silt‐ and clay‐sized particles. A two‐component model fitted to the data yielded a rapidly mineralizable C pool (about 20% of total C) and a slowly mineralizable pool (about 80%). Generally, the size of the rapidly mineralizable C pool was rather small because inorganic N was rapidly immobilized after the addition of maize. However, the different mean half‐lives of the C pools (rapidly decomposable mixed 0.035 years, and surface‐applied 0.085 years; slowly decomposable mixed 0.96 years, and surface‐applied 1.7 years) showed that mineralization was delayed when the straw was left on the surface. This seems to be because there is little contact between the soil microflora and plant residues. Evidently, the organic matter is more decomposed and protected within soil inorganic compounds when mixed into the soil than when applied on the soil surface, despite similar rates of mineralization.

Carbon and nitrogen contents in particle–size fractions of topsoil along a 3000 km aridity gradient in grasslands of northern China

“…This pattern, which may be caused because fine fractions in soil have high surface area which can enhance formation of organo-mineral complexes that protect SOM from microbial degradation (Hassink, 1997;Zhang and Liu, 2010), supports previous findings that soil fractionation is a useful tool for examining different C and N pools in soil (Amelung et al, 1998;Gerzabek et al, 2001;Stemmer et al, 1999). Across the transect, we observed that C and N concentrations and stocks in bulk soils were negatively correlated with sand content and positively correlated with silt and clay contents.…”

How can straw incorporation management impact on soil carbon storage? A meta-analysis

“…Li et al (2001) reported straw decomposition rates were closely related to SI depths, in decreasing order from 5 to 15 cm to the surface soil. Thus, compared with NT, tillage treatments have increased the potential to promote straw C conversion into soil C (Stemmer et al 1999;Wingeyer et al 2012). It is noteworthy that NT treatment generally results in greater soil C storage than PT and RT treatments at surface soil (Bossuyt et al 2002;Dolan et al 2006;Huggins et al 2007;Hermle et al 2008).…”

Tillage impacts on the fractions and compositions of soil organic carbon

“…Second, many reports concluded that SOC concentration of different aggregates was higher for NT and RT (ridge tillage, similar to DT) compared with PT in the depth of 0-5 cm, nevertheless, the inverse effects was found in the depth of 5-20 cm or 10-15 cm (Six et al, 1999;Zibilske and Bradford, 2007). Similar researches deduced that more SOC concentration from the maize conveyed into the stable SOC in tilled soil than untilled soil, and favoring formation in the micro-aggregates (Stemmer et al, 1999).…”