Soil Aggregates, C, and N As Affected by 24 Years of Differing Levels of Crop Residue and Fertilizer Inputs.

The soil organic carbon (SOC) and N (SON), aggregate stability and microbial diversity are indicators of good soil ecosystem health and environmental stability and is affected by management.  Aggregate stability is one of the soil properties that are most sensitive to change in management practices.  A residue harvest study was conducted at the Kansas State University’s East Central Experiment field near Ottawa, KS on a 0-1% slope, Woodson silt loam soil (fine, montmorillonitic, thermic, Abruptic Argiaquoll). Residue levels were 0X, 1X, and 2X and three fertilizer levels were maintained for 24years. Soil samples collected to a depth of 30 cm were analyzed for aggregate stability and SOC and SON. The maccroaggregates (>2000µm and 2000-250µm) were highest (100-250g/kg) and (95-230g/kg) in 2X and 1X respectively and lowest (50-200g/kg) in the 0X residue level. The most abundant aggregate size fraction was that [53-250 µm] in diameter at 0-5 and 5-15cm but at 15-30cm; the maccroaggregates [250-2000 µm] were the most abundant aggregate size fraction. This fact was independent of the residue treatments, fertility level or cropping succession. After 24years, soil organic carbon was lower in the 0X level in the top 5cm compared to 1X and 2X. These slowly occurring effects are potentially a threat to the sustainability of the soil in the longer-term. Maintaining or doubling crop residues in combination with fertilizer inputs did not statistically show significant difference for SOC and N. The results show that greater inputs of inorganic N and increased returns of crop residues did not cause a proportionately greater increase in SOC.

See more from this Division: S03 Soil Biology & Biochemistry
See more from this Session: Carbon, Nitrogen, and Microbial Responses to Cropping and Management Systems

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