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To identify efficient field management practices for enhanced soil carbon sequestration suited to crop rotation-based Andosol fields in northern Japan, the impacts of a combination of tillage, fertilizer type, and plant residue input on soil carbon sequestration rates were studied in a 4-year field experiment (April 2007 to March 2011). The rates of changes in soil organic carbon over the entire study period were determined by soil carbon stock change and by net ecosystem carbon budget. Across eight field management treatments and two replicates for each treatment, the rates of changes in soil organic carbon determined by net ecosystem carbon budget were positively correlated with the rates determined by soil carbon stock change (r = 0.766,n = 16). The arithmetic means of the rates determined by net ecosystem carbon budget (1.24 Mg C ha−1 year−1) were greater than those determined by soil carbon stock change (−0.18 Mg C ha−1 year−1) because decomposing crop residues and composted cattle manure in soil were included in the calculation of the net ecosystem carbon budget but were excluded in the calculation of soil carbon stock change (decomposing crop residues and composted cattle manure in soil samples were removed by sieving in measuring the soil carbon stock change). Both methods led to the same conclusion that soil carbon sequestration was significantly enhanced by composted cattle manure application and increased input of plant carbon from crop residues and green manure but was not enhanced by reduced tillage. Thepvalues for net ecosystem carbon budget were smaller than those for soil carbon stock change in analysis of variance; therefore, the net ecosystem carbon budget was more sensitive to field management practice than the soil carbon stock change. [ABSTRACT FROM PUBLISHER]

Abstract: Soil C sequestration in croplands is deemed to be one of the most promising greenhouse gas mitigation options for Japan''s agriculture. In this context, changes in soil C stocks in northern Japan''s arable farming area over the period of 1971–2010, specifically in the region''s typical Andosol (volcanic ash-derived) and non-Andosol soils, were simulated using soil-type-specific versions of the Rothamsted carbon model (RothC). The models were then used to predict the effects, over the period of 2011–2050, of three potential management scenarios: (i) baseline: maintenance of present crop residue returns and green manure crops, as well as composted cattle manure C inputs (24–34 Mgha−1 yr−1 applied on 3–55% of arable land according to crop), (ii) cattle manure: all arable fields receive 20 Mgha−1 yr−1 of composted cattle manure, increased C inputs from crop residues and present C inputs from green manure are assumed, and (iii) minimum input: all above-ground crop residues removed, no green manure crop, no cattle manure applied. Above- and below-ground residue biomass C inputs contributed by 8 major crops, and oats employed as a green manure crop, were drawn from yield statistics recorded at the township level and crop-specific allometric relationships (e.g. ratio of above-ground residue biomass to harvested biomass on a dry weight basis). Estimated crop net primary production (NPP) ranged from 1.60 Mg Cha−1 yr−1 for adzuki bean to 8.75 Mg Cha−1 yr−1 for silage corn. For the whole region (143×103 ha), overall NPP was estimated at 952±60 Gg Cyr−1 (6.66±0.42 Mg Cha−1 yr−1). Plant C inputs to the soil also varied widely amongst the crops, ranging from 0.50 Mg Cha−1 yr−1 for potato to 3.26 Mg Cha−1 yr−1 for winter wheat. Annual plant C inputs to the soil were estimated at 360±45 Gg Cyr−1 (2.52±0.32 Mg Cha−1 yr−1), representing 38% of the cropland NPP. The RothC simulations suggest that the region''s soil C stock (0–30cm horizon), across all soils, has decreased from 13.96 Tg C (107.5 Mg Cha−1 yr−1) in 1970 to 12.46 Tg C (96.0 Mg Cha−1 yr−1) in 2010. For the baseline, cattle manure and minimum input scenarios, soil C stocks of 12.13, 13.27 and 9.82 Tg C, respectively, were projected for 2050. Over the period of 2011–2050, compared to the baseline scenario, soil C was sequestered (+0.219 Mg Cha−1 yr−1) by enhanced cattle manure application, but was lost (−0.445 Mg Cha−1 yr−1) under the minimum input scenario. The effect of variations of input data (monthly mean temperature, monthly precipitation, plant C inputs and cattle manure C inputs) on the uncertainty of model outputs for each scenario was assessed using a Monte Carlo approach. Taking into account the uncertainty (standard deviation as % of the mean) for the model''s outputs for 2050 (5.1–6.1%), it is clear that the minimum input scenario would lead to a rapid decrease in soil C stocks for arable farmlands in northern Japan. [Copyright &y& Elsevier]

Soil carbon sequestration in agricultural lands has been deemed a sustainable option to mitigate rising atmospheric CO2 levels. In this context, the effects of different tillage and C input management (residue management and manure application) practices on crop yields, residue C and annual changes in total soil organic C (SOC) (0–30 cm depth) were investigated over one cycle of a 4-year crop rotation (2003–2006) on a cropped Andisol in northern Japan. For tillage practices, the effects of reduced tillage (no deep plowing, a single shallow harrowing for seedbed preparation [RT]) and conventional deep moldboard plow tillage (CT) were compared. The combination of RT, residue return and manure application (20 Mg ha−1 in each year) increased spring wheat and potato yields significantly; however, soybean and sugar beet yields were not influenced by tillage practices. For all crops studied, manure application enhanced the production of above-ground residue C. Thus, manure application served not only as a direct input of C to the soil, but the greater crop biomass production engendered enhanced subsequent C inputs to the soil from residues. The SOC contents in both the 0–5 cm and 5–10 cm layers of the soil profile were greater under RT than under CT treatments because the crop residue and manure were densely incorporated into the shallow soil layers. Comparatively, neither tillage nor C input management practices had significant effects on annual changes in SOC content in either the 10–20 cm or 20–30 cm layers of the soil profile. When soil C sequestration rates, as represented by annual changes in total SOC (0–30 cm), were assessed on a total soil mass basis, ananova showed that tillage practices had no significant effect on total C sequestration, but C input management practices had significant positive effects ( P ≤ 0.05). These results indicate that continuous C input to the soil through crop residue return and manure application is a crucial practice for enhancing crop yields and soil C sequestration in the Andisol region of northern Japan. [ABSTRACT FROM AUTHOR]