Bark manure and crop residues have been applied for 30 years to upland fields with a light-colored Andosol in Hokkaido. The cropping system consisted of sugar beets, soybeans, spring wheat, and potatoes. We investigated changes in total carbon, total nitrogen, and the physical characteristics of the soil as a function of the application rates of these organic materials. The dry weight of the applied organic matter (DWAOM) was highly correlated with the resulting change in total carbon and total nitrogen (r=0.987 and r=0.983, respectively). Total carbon and total nitrogen decreased by about 10% with no application of organic matter, but remained constant with the application of about 2.5Mg DWAOM ha^<-1> year^<-1>. In contrast, the application of 5Mg DWAOM ha^<-1> year^<-1> increased total carbon and total nitrogen by about 10%. The application of organic matter decreased soil density and compaction, and DWAOM was closely correlated with bulk density and the solid phase. DWAOM was also strongly correlated with the gaseous phase, available moisture, and water-stable macroaggregates. The application of organic matter improved air permeability and water retention. The bark manure and the crop residues fell on the same regression line of the relationships between DWAOM and total carbon and soil physical characteristics; therefore, in terms of soil improvement, there appeared to be no difference between these two kinds of organic matter.

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Organic fertilizer (OF) is widely applied in paddy fields because of a growing environmental consciousness among farmers. However, no studies have examined the effect of easily decomposable OF on the cold tolerance of rice plants. In this study, we examined the effects of easily decomposable OF on anther length and the number of engorged pollen grains, as these characteristics are closely related to cold injury. Readily available inorganic fertilizer (RAF) and controlled-availability inorganic fertilizer (CAF) were used as controls. During our observations in 2005 and 2006, air temperatures were not sufficiently low to damage rice plants. In 2005, the number of engorged pollen grains ranged from 1089 to 1319 per anther in the RAF plots, versus 1291 to 1351 in the OF plots (an increase of approximately 10%). The number of pollen grains in the CAF plot was 1389, similar to that in the OF plots. In 2006, the number of pollen grains ranged from 1016 to 1137 in the RAF plots, versus 1197 to 1239 in the OF plots. Anther length was longer in the OF and CAF plots than in the RAF plots. The number of engorged pollen grains in the RAF plots was significantly negatively correlated with the number of rice grains per square meter, whereas those in the OF and CAF plots showed no correlation. Thus, the number of engorged pollen grains in the OF and CAF plots was greater than that in the RAF plots at the same grain density. Furthermore, the number of engorged pollen grains in the RAF plots was significantly negatively correlated with the nitrogen content of the shoots at meiosis (a factor that was most sensitive to cold weather), whereas those in the OF and CAF plots showed no correlation. These results suggest that the slow release of nitrogen from OF and CAF increased anther length and the number of engorged pollen grains.

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Water pollution that seriously harms human health is reported to occur when the amount of nitrate nitrogen (N) in water exceeds 10mg L^<-1>. The source of dissolved nitrate N in agricultural areas is often fertilizer and hog or cattle dung. The rate of percolation through the soil affects leaching losses of nitrate N, and the high percolation rates in sandy soils leads to high leaching losses, which in turn increase the risk to human health. Carbide is commonly used to prevent the loss of nitrate N.In this study, we evaluated the effect of carbide soil amendments that originated from risk husk (Cc) or bran (Bc), with and without iron (III) chloride (Fe), on the growth of crops and leaching of nitrate N from sandy soils. The Cc amendment, with or without Fe, had no effect on the leaching of nitrate N in a model experiment compared with the amount of leaching in the absence of carbide. Less nitrate N was leached in the Bc treatment, with or without Fe (Bc+Fe and Bc, respectively), in the model experiment. The anion-exchange capacity (AEC) in the Bc+Fe treatment was 15 to 20cmol(-)kg^<-1>, but was negligible in the Bc treatment. The lower leaching of nitrate N in the Bc+Fe treatment may thus have been caused by the higher AEC, whereas the reduced leaching in the Bc treatment may have been caused by the porous structure of the Bc. The leaching of nitrate N was lower in the Bc and Bc+Fe treatments in both the pot and field experiments without carbide amendment. Plants grown in a pot experiment with Bc or Bc+Fe treatments and plants grown in the field experiment with the Bc+Fe treatment grew better than plants without a carbide amendment. This suggests that crops could more readily absorb nitrate N adsorbed by Bc+Fe or Bc in both the pot and field experiments.

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We examined the effects of combined applications of ^<15>N-labeled ammonium sulfate and cattle composts on nitrogen dynamics under upland soil conditions in comparison with a single application of compost or of ^<15>N-labeled ammonium sulfate in incubation experiments. The amount of inorganic nitrogen (N) derived from the ammonium sulfate was smaller in the combined application than in the single application, indicating that some N derived from the ammonium sulfate was immobilized. The degree of immobilization was correlated with the amount of easily decomposable carbon (C) in the compost. Immobilized N tended to be re-mineralized during the incubation. The 1-month N mineralization rates of the composts increased by 5% to 10% after the application of ammonium sulfate. This increase was negatively correlated with the C/(N+fAN) ratio, where C and N represent the C and N contents derived from the compost, and fAN represents the amount of N derived from the ammonium sulfate. These results suggest that the pattern of N mineralization from compost was changed by the application of N fertilizer. Appropriate application rates can thus be calculated from the C/(N+fAN) ratio. In addition, it will be necessary to select composts that induce little immobilization of applied fertilizer N.

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Litter decomposition and acid buffering reactions influence the dynamics of base cations in the organic horizon of a forest floor. However, traditional litter-bag methods cannot evaluate the amounts of base cations that are leached during litter decomposition. To resolve this problem, we developed a new method that allows measurements of the nutrient budget and litter decomposition rate. In the new method, leaf litter is placed in a stainless steel "litter lysimeter" to which an outlet tube filled with ion-exchange resin is connected. We evaluated the applicability of this method by comparing decomposition rates of leaves of Cryptomeria japonica incubated in litter lysimeters and in nylon-net litter bags for 10 months. We also compared the changes in the amounts of total and exchangeable base cations in the residual litter samples. The decomposition rates of the litter samples did not differ significantly between the two methods. Total calcium (Ca) contents in the litter samples increased after the 10-month incubation in both methods. The exchangeable calcium (Ca^<2+>) contents increased throughout the incubation in both methods, and were negatively correlated with the amount of residual litter. Total magnesium decreased after 10 months of incubation in both methods. However, there was no significant correlation between the amount of residual litter and the exchangeable magnesium (Mg^<2+>) content, which suggests that the Mg^<2+> content in the residual litter was affected by the nutrient budget. Based on these results, we conclude that the decomposition behavior of leaf litter and the dynamics of exchangeable Ca^<2+> can be estimated equally well using the litter lysimeter and litter-bag methods. The litter lysimeter method will thus serve as a useful tool for evaluating Ca dynamics during litter decomposition on the forest floor.

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[in Japanese]

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