Carbon mineralization in subtropical alluvial arable soils amended with sugarcane bagasse and rice husk biochars

Subtropical recent alluvial soils are low in organic carbon(C).Thus,increasing organic C is a major challenge to sustain soil fertility.Biochar amendment could be an option as biochar is a C-rich pyrolyzed material,which is slowly decomposed in soil.We investigated C mineralization(CO_(2)-C evolution)in two types of soils(recent and old alluvial soils)amended with two feedstocks(sugarcane bagasse and rice husk)(1%,weight/weight),as well as their biochars and aged biochars under a controlled environment(25±2℃)over 85 d.For the recent alluvial soil(charland soil),the highest absolute cumulative CO_(2)-C evolution was observed in the sugarcane bagasse treatment(1140 mg CO_(2)-C kg^(-1)soil)followed by the rice husk treatment(1090 mg CO_(2)-C kg^(-1)soil);the lowest amount(150 mg CO_(2)-C kg^(-1)soil)was observed in the aged rice husk biochar treatment.Similarly,for the old alluvial soil(farmland soil),the highest absolute cumulative CO_(2)-C evolution(1290 mg CO_(2)-C kg^(-1)soil)was observed in the sugarcane bagasse treatment and then in the rice husk treatment(1270 mg CO_(2)-C kg^(-1)soil);the lowest amount(200 mg CO_(2)-C kg^(-1)soil)was in the aged rice husk biochar treatment.Aged sugarcane bagasse and rice husk biochar treatments reduced absolute cumulative CO_(2)-C evolution by 10%and 36%,respectively,compared with unamended recent alluvial soil,and by 10%and 18%,respectively,compared with unamended old alluvial soil.Both absolute and normalized C mineralization were similar between the sugarcane bagasse and rice husk treatments,between the biochar treatments,and between the aged biochar treatments.In both soils,the feedstock treatments resulted in the highest cumulative CO_(2)-C evolution,followed by the biochar treatments and then the aged biochar treatments.The absolute and normalized CO_(2)-C evolution and the mineralization rate constant of the stable C pool(K_(s))were lower in the recent alluvial soil compared with those in the old alluvial soil.The biochars and aged biochars had a negative priming effect in both soils,but the effect was more prominent in the recent alluvial soil.These results would have good implications for improving organic matter content in organic C-poor alluvial soils.

Mulching type-induced soil moisture and temperature regimes and water use efficiency of soybean under rain-fed condition in central Japan

Soybean(Glycine max)is a high water-demand crop and grown under moderate temperature in Japan.To protect the crop from hot summer and to utilize rainfall for its cultivation,selection of appropriate mulching material(s)is crucial.For optimum production of the crop,soil moisture and temperature regimes as well as water use efficiency(WUE)of the crop were investigated under straw,grass,paper,plastic and bare soil(control)mulching under rain-fed condition at Gifu university farm in Japan.The mulching treatments,compared to the control,lowered soil temperature by 2°C at 5 cm depth and 0.5°C at 15 and 25 cm depths.The plastic and straw mulching stored the highest quantity of soil moisture at 5 and 15 cm depths;the bare soil stored the lowest quantity.At 25 cm depth,soil-moisture content was the highest under paper mulch but invariable under the other mulches.Plastic mulching reduced evaporation rate from the soil surface and,consequently,the reduced soil-water consumption(SWC)from the root zone augmented WUE of soybean.The paper mulching,by conserving soil-moisture and reducing soil temperature,provided better crop growth attributes,while the plastic mulching improved WUE of green soybean.Therefore,the plastic mulch performed best in reducing soil-water consumption and increasing WUE,while the paper mulch was good for soil-moisture conservation and temperature modification that increased soybean yield.