Enumeration of carbon and nitrogen contents of water-stable aggregates in layers of topsoils from cultivated and adjacent bush-fallow loamy soils

Soil organic carbon (SOC) and total soil nitrogen (TSN) dynamics have both pedological and agronomic basis. Knowledge of their retention within aggregate hierarchies of varying soil textures as influenced by land use change is limited. The capacity of loam (L), clay loam (CL), sandy loam (SL) and sandy clay loam (SCL) soils to retain SOC and TSN in water-stable aggregate (WSA) at 10-cm intervals of 0-30 cm topsoil depths under cultivated and bushfallow/ uncultivated systems was investigated. The soils showed high dispersion ratio and great variations in aggregate silt and clay indices (CL > L > SCL > SL) under both land uses. Across soil depths, the uncultivated CL, SL and SCL soils had moderate to high > 2.00 mm WSA whose reduction due to cultivation impact was more pronounced in SL than in CL soil. Across soil depths and land uses, SOC content seemed higher in the macro- (> 0.50 mm) than in the micro- (< 0.50 mm) aggregates of all the soils while the reverse marked aggregate TSN content in almost all the soils. Cultivation mostly reduced macro-aggregate-associated SOC and TSN in L > CL > SL and in L > SL > CL > SCL soils, respectively. However, cultivation showed no reduction influence on micro-aggregate-associated SOC of all the soils. Cultivation-related reduction in micro-aggregate-associated TSN was more pronounced in the generally more ‘clayey’ CL and SCL than the L and SL soils. So, the potential of bush-fallowing to enhance micro-aggregateassociated TSN storage and stabilization against adverse influence of cultivation depends on soil texture.

Distribution characteristics and stability of soil aggregates as compounded by soft rock and sand under different planting years of corn in Mu Us sandy land in China

Field plot experiments of compound soil mixing with soft rock and sand with ratios of 1 : 1, 1 : 2 and 1 : 5 during 2010-2018 years of corn cultivation in Mu Us Sandy Land in china., was carried out to observe the change characteristics of composition, distribution and mean weight diameter (MWD) of compound soil water stable aggregate (WSA) under different corn planting years. The results showed that with the increase of planting years, the content of WSA in composite soils of three portions with a particle size of < 0.25 mm gradually decreased, and WSA with a particle size of > 0.25 mm showed a continuous increasing trend. The WSA with a particle size of 0.25 - 0.5 mm accounted high for the maximum ratio, which plays an important role in the agglomeration of the compound soil. After 9 years of planting, the MWD of 1 : 1, 1 : 2 and 1 : 5 compound soil WSA increased by 1.13, 1.85 and 1.58 times, respectively, and t 1:2 compound soil WSA with particle size > 0.25 mm and MWD increase at a faster rate, which lead to a higher soil agglomeration and stability. The interaction between the mixture ratio of soft rock to sand and the planting years of corn has a significant impact on the formation and stability of WSA in the compound soil. With the increase of planting years of corn, the agglomeration effect of compound soil in different proportions was found to enhance, and the development of soil structure improve continuously. Bangladesh J. Bot. 50(3): 917-923, 2021 (September) Special

Impact of Effective Microorganisms (EM) Application on the Physical Condition of Haplic Luvisol

The study set out to determine changes in the soil air-water properties, the water-stable aggregate share and organic carbon content as effects of a five-year application of effective microorganisms (EM-A). The hypothesis that long-term applied EM-A biopreparations have a positive effect on the soil physical condition has not been confirmed. Haplic Luvisols originating from silt were studied in a field experiment after EM-A biopreparation treatment. The soil samples with the natural structure preserved intact were collected three times each year. The properties of the soil determined in the study were: particle density, total organic carbon content, bulk density, total porosity, air capacity, air permeability, soil moisture at sampling, field water capacity, available water content, unavailable water content, and water-stable aggregate content. The ratio of field water capacity and total porosity (FC/TP) was calculated. It was found that EM-A application primarily leads to a decrease in the content of organic carbon and water-stable aggregates. This was an adverse effect. Total organic carbon (TOC) and water-stable aggregates proved to be very sensitive indicators for assessing the soil physical condition. However, changes in soil compaction and air–water properties did not show significant deterioration. Our research addresses the data gaps about EM application to soil.

Effects of Biochar Combined with Nitrogen Fertilizer Reduction on Rapeseed Yield and Soil Aggregate Stability in Upland of Purple Soils

Reduction of soil fertility and production efficiency resulting from excessive application of chemical fertilizers is universal in rapeseed-growing fields. The main objective of our study was to assess the effects of biochar combined with nitrogen fertilizer reduction on soil aggregate stability and rapeseed yield and to identify the relationship between yield and soil aggregate stability. A two-factor field experiment (2017–2019) was conducted with biochar (0 (C0), 10 (C10), 20 (C20) and 40 t·ha−1 (C40)) and nitrogen fertilizer (180 (N100), 144 (N80) and 108 kg N·ha−1 (N60)). Experimental results indicated that under N100 and N80 treatments, C10 significantly increased the macro-aggregates (R0.25), mean weight diameter (MWD) and geometric mean diameter (GMD) of soil water stable aggregate by 14.28%–15.85%, 14.88%–17.08% and 36.26%–42.22%, respectively, compared with C0. Besides, the overall difference of the soil water-stable aggregate content in 2–5 mm size range among nitrogen treatments was significant under the application of C10, which increased by 17.04%–33.04% compared with C0. Total organic carbon (TOC) in R0.25 of soil mechanical-stable aggregates was basically all increased after biochar application, especially in 0.25–1 mm and 1–2 mm aggregates, and had an increasing trend with biochar increase. C10 significantly increased rapeseed yield by 22.08%–45.65% in 2019, compared with C0. However, the reduction of nitrogen fertilizer reduced the two-year average rapeseed yield, which decreased by 11.67%–31.67% compared with N100. The highest yield of rapeseed was obtained by N100C10 in two consecutive years, which had no statistical difference with N80C10. However, the two-year yields of N80C10 were all higher than those of N100C0 with increase rate of 16.11%, and which would reduce 35.43% nitrogen fertilizer in the case of small yield difference, compared with the highest yield (2.67 t·ha−1) calculated by multi-dimensional nonlinear regression models. The regression analysis indicated R0.25, MWD and GMD had the strong positive associations with rapeseed yield, whereas percentage of aggregate destruction (PAD0.25) had a significant negative correlation with rapeseed yield. This study suggests that the application of biochar into upland purple soil could improve soil structure, increase the content of TOC in macro-aggregates under nitrogen fertilizer reduction as well as replace part of nitrogen fertilizer to achieve relatively high rapeseed yield.