Structural Stability Conditions Soil Carbon Gains from Compost Management and Rotational Diversity

Core Ideas Soil structure and carbon pools were quantified in a 20‐year field crop trial. Compost management influenced soil aggregate size, labile carbon, and total carbon. An increased rotational diversity from one to five crops enhanced soil aggregate stability. Use of moderate compost increased soil carbon by 20% relative to fertilizer. Understanding processes that underlie soil carbon gains and enhance structural stability is key to sustainable production of intensively managed row crops. Long term consequences of crop diversity and interactions with compost management have rarely been tested with economically feasible, moderate rates of organic amendments. We investigated soil aggregation and carbon pools over twenty years on a field crop experiment that allowed quantification of the impact of rotational diversity within two integrated management regimes, one based on compost (3 Mg ha⁻¹) and the other inorganic fertilizer, both at about 100 kg N ha⁻¹ annually. The Living Field Laboratory (LFL) experimental study where the study was conducted is located at the W.K. Kellogg Biological Station in southwest Michigan. The rotational diversity treatments investigated included continuous corn (Zea mays L.) (CC), corn–soybean [Glycine max (L.) Merr.] rotation (CS), corn–soybean–wheat (Triticum aestivum L.) rotation (CSW), and corn–soybean–wheat rotation with a cover crop (CSWco). Soil C status in 1993 was 2584 g m⁻² and by 2013 increased in integrated fertilizer and compost plots to 3026 and 3672 g kg⁻¹, respectively. Compost management enhanced soil labile C, organic C and the proportion of large macroaggregates (>2000 μm size fraction). Rotational diversity did not influence total soil C but was positively associated with soil aggregate stability and aggregate carbon pool size. The study findings were consistent with integrated organic and inorganic nutrient management as interacting positively with crop diversity, to support gains in soil structural stability and C accrual.