Japanese Journal of Soil Science and Plant Nutrition

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No-tillage and No-ridge soybean cultivation has advantages of labor conservation, improved working efficiency, reduced germination of weeds, reducing costs, preventing soil erosion and timely sowing, and mainly large-scale farmers have adopted this technology. In order to make appropriate soil management in it, it is important to know the changes in the soil physical and chemical properties. In Japan, however, limited experiments on this technology are reported. For the purpose of establishing a proper management of soil in continuous no-tillage and no-ridge cultivation of soybean, we investigated the physical and chemical changes of soil from 2003 to 2008. The results obtained were as follows. 1) Bulk density at 5〜22cm layer of no-tillage soil was higher than tillage soil, but lower in 0〜5cm layer. Amount of soil in 0〜30cm layer of no-tillage soybean cultivation increased by 4.3% during 6 years and that of tillage cultivation increased by 4.1%. 2) In surface soil (0〜5cm), T-C and T-N of no-tillage soil was higher than those of tillage soil. In 14〜30cm layer that was not plowed, however, the difference between the two methods was not observed. 3) The T-C and Av-N greatly decreased in four years in both methods and changed gently afterwards. They seemed to be converged at a certain value. 4) The decrease of T-C in 0〜30cm layer of no-tillage soil during 6 years was 2.5Mg ha^<-1>, less than half that of tillage soil (5.7Mg ha^<-1>). The Av-N in no-tillage soil was 28% higher than that in tillage soil. These indicate that no-tillage cultivation contributes to maintaining C level and N availability. 5) The ex-CaO increased in each soil layer due to the application of lime materials in both methods, especially in the surface soil (0〜5cm) of the no-tillage cultivation. On the other hand, in 0〜22cm layer, ex-K_2O decreased greatly in both methods. 6) Av-P_2O_5 was increased in each layer in both methods. It was thought that the Ca type phosphate was increased by application of lime materials. Oppositely, T-P_2O_5 was decreased in each layer. As accumulation of T-P_2O_5 in lower layers was not observed, it might be effused outside the field by downward water. In continuous no-tillage and no-ridge cultivation of soybean after paddy rice, soil C and Av-N decreased. No-tillage cultivation, therefore, is more sustainable than conventional tillage cultivation. It is necessary to apply K and P materials because ex-K_2O and T-P_2O_5 was greatly decreased.

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We investigated the water quality and hydrological conditions in the Arata River, a tributary of the Umeda River which flows into Mikawa Bay. The Arata river basin has a wide distribution of red-yellow soil and large acreage of vegetable and paddy rice cultivations (54% and 15% of the basin area, respectively), and are raised by 4,500 hogs and 580 cattle as well. The concentrations of total nitrogen (TN) and NO_3^--N concentrations of the river water decreased concomitantly with those of SiO_2 and some major fertilizer elements except for phosphorus, as the discharge increased during rainfall events. The concentrations of total phosphorus (TP), particulate phosphorus (PP) and suspended solids (SS) increased remarkably during the events. The concentrations of SS and PP showed strong positive correlation. N and P concentrations of the base flow were relatively low in summer. This could be because of the dilution of the basin effluent with the Toyogawa irrigation water which has extremely low average N and P concentrations of 0.6mg L^<-1> and 0.02mg L^<-1>, respectively. In contrast, their concentrations increased during winter because of reduced amounts of irrigation water supply after the rice cultivation period and the nitrogen-purifying efficiency of livestock wastewater treatment facilities due to low temperature in winter. N runoff was found at all times regardless of flow conditions, while considerable P and SS loads were observed only during heavy rainfall events, that is precipitations of more than 50mm d^<-1>. The annual loads of TN, TP, and SS were estimated to be 19.2, 2.0, and 242Mg km^<-2> y^<-1>, respectively. 89% for TN and 94% for NO_3^--N and NH_4^+-N of total loads were derived from the base flow. On the contrary, 53%, 84%, and 94% for TP, PP, and SS, respectively, were derived from direct runoffs during rainfall events.

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Nitrogen leaching, uptake, and accumulation in the soil were examined by using ^<15>N tracer techniques in Andisol monolith lysimeters (1m in depth) receiving ammonium sulfate fertilizer (AF) or cattle manure compost (CM) for 2.5 years. The combinational application treatments of AF and CM were also included to examine the mutual effect of the materials on the fate of nitrogen. For the first crop, Komatsuna (Brassica rapa var. peruviridis), the AF labeled with ^<15>N, ^<15>N-labeled AF and unlabeled CM, ^<15>N-labeled CM, or ^<15>N-labeled CM and unlabeled AF were applied on each monolith lysimeter. Each application rate of the labeled and unlabeled materials was 15g-N m^<-2>. Unlabeled materials were used for all treatments in the later four crops, corn (Zea mays), and spinach (Spinacia oleracea) for two years. The following results were obtained: 1) Leaching of nitrogen derived from labeled materials began before water percolated as much as the water retained in a monolith at the beginning of the examination, and lasted more than 1 year. Leaching of nitrogen derived from labeled AF was 1.5-2.4g m^<-2>, and it from labeled CM was 0.3-0.4g m^<-2>. 2) Nitrogen derived from labeled AF leached mainly in the 2nd year. The 2nd crop removed 2.9-3.6g m^<-2> of nitrogen derived from labeled AF. These results indicate that uptake of nitrogen that remained in the soil monoliths by the following crops can improve the recovery rate of the applied nitrogen. 3) Nitrogen derived from labeled CM accumulated approximately 12g m^<-2> in the soil, and about the same proportion of ^<15>N derived from labeled CM was found in all the crops. This indicates that nitrogen derived from CM should account for more proportion of the nitrogen uptake and leaching, when CM was continuously applied. 4) As in the sandy soil (Ihara et al., 2009), co-application of AF and CM accelerated the uptake of nitrogen derived from CM and retarded it derived from AF.

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To determine total bromine (Br) content in soils, a simple and sensitive method was developed by combining extraction of soils with alkali solution with the analysis of 2-bromo-3-pentanone using high performance liquid chromatography (HPLC). A 0.2-0.3g of finely ground soil sample was mixed with 2mL of 0.225g mL^<-1> NaOH solution and 0.5mL of 1% MgO solution and heated at 500℃ for 90min. After cooling, the sample was mixed with 10mL of water and 8mL of the solution was mixed with 2mL of 2.5mol L^<-1> sulfuric acid to make sample solution. To the sample solution, 0.5mL of 5mol L^<-1> sulfuric acid, 0.5mL of 0.1mol L^<-1> potassium permanganate solution and 0.5mL of 5% 3-pentanone solution were added successively to oxidize Br^- and to react Br_2 with 3-pentanone. The resulting 2-bromo-3-pentanone was extracted with 4mL of hexane for 3min. and the concentration of 2-bromo-3-pentanone was determined with HPLC at 305nm as the area or height of the peak with the capacity factor of about 2.3. This method enabled quantitative differentiation of Br from Cl and I and the recovery rates of Br^- and BrO_3^- added were 105% and 107%, respectively. The repeated measurement of 4 standard soil samples indicated that the data obtained by the analytical method were reasonably in good agreement with reference data, with their coefficients of variation of 5.6-8.9%. Total Br contents of 11 agricultural soils in Japan by this method were almost identical to those by energy-dispersive X-ray fluorescence spectrometry (EDXRF).

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