We investigated the pest control effects of a soil-reducing disinfection method using sweet corn residues on root-knot nematodes (Meloidogyne microcephala) and on the chemical characteristics of the soil. The nematode control effects of this method were comparable to or better than those of a similar method using rice bran. After the disinfection, delayed-start culture enabled us to reduce the use of manufactured fertilizers by 60-90 kg・ha^<-1> of nitrogen and 120-180 kg・ha^<-1> of potassium. With the small amount of phosphoric acid fed, this method is suitable for soils with an excessive phosphate content. It also helps decrease the eluviation of nitrate-nitrogen remaining in the soil after cropping.

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To investigate the potential of carbonized sewage sludge as biochar in agricultural production and grassland conservation, we examined its physico-chemical properties and effects on plant growth. Sewage sludge was burned anaerobically for 20 min at about 800 ℃. The product comprised small black particles with an average diameter of 1.4 mm. With a water content of 1.8% and a bulk density of 0.60 g cm^<-3>, it would be easy to handle. A 1:5 water extract had a pH of 7.2 and an electrical conductivity of 1.1 mS cm^<-1>. Its cation exchange capacity was about 14 cmolc kg^<-1>, suggesting a moderate nutrient-holding capacity. Its water-extractable fraction was mainly CaSO_4 and MgSO_4, whereas its 0.1 mol L^<-1>-extractable fraction was mainly Ca, Mg, and Al phosphates. Among the major elements it contained 209 g C kg^<-1>, 84.9 g Si kg^<-1>, 78.9 g P kg^<-1> (relatively high), 72.4 g Al kg^<-1>, 62.0 g Fe kg^<-1>, and 51.1 g Ca kg^<-1>. Among the minor elements it contained 1630 mg Zn kg^<-1>, 1100 mg Cu kg^<-1>, 126 mg Ni kg^<-1>, 92 mg Cr kg^<-1>, 24 mg Pb kg^<-1>, and 4 mg Cd kg^<-1>. Concentrations of Cd, Cr, Pb, and As were within the limits legislated in Japan, suggesting a low risk of contamination of soil with these elements through application to fields. Application of carbonized sewage sludge significantly increased the growth of Begonia semperflorens on sand-dune soil and yellow soil with low physico-chemical properties (P<0.01, P<0.05). Thus, carbonized sewage sludge could be an effective soil amendment for improving agricultural production and for grassland conservation.

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To analyze the influence of early leaf fall during the ripening period of soybean on yield and 100-grain weight, we pruned leaf blades and petioles at 20, 15, and 10 days before maturity (DBM) in 2004, and at 20, 15, and 9 DBM in 2006. The nitrogen contents of the leaves decreased in the order of 20, 15, and 10/9 DBM. In contrast, those of stems, pods, and seeds at maturity decreased in the order of control (no pruning), 10/9, 15, and 20 DBM. Consequently, the total nitrogen content (pruned leaf blades, petioles, stems, pods, seeds) did not change. The yield and number of seeds 5.5-7.3 mm long decreased in the order of 20, 15, 10/9 DBM, and control. In contrast, those of seeds >7.9 mm long increased in that order. The 100-grain weight showed different tendencies between years. Consequently, increasing the loss of nitrogen favored the production of smaller seeds over larger seeds.

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The use of methane-fermentation-digested slurry as a liquid fertilizer can reduce operating costs for methane fermentation plants and reduce the use of applied fertilizer. We evaluated the influence of application method on emissions of NH_3 and N_2O in laboratory experiments. The digested slurry was either applied to the soil surface or incorporated into the soil. NH_3 emissions peaked immediately after surface application, and approximately 80% of the applied NH_4^+ was lost in 5 days. In contrast, incorporation inhibited NH_3 volatilization, and emissions were negligible. However, when the soil was relatively wet, allowing nitrification of the NH_4^+, more N_2O was lost from the incorporation plot than from the surface application plot. Thus, there was a trade-off between NH_3 and N_2O emissions by application method, so incorporation in wet soils may contribute more to global warming.

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The Sujikai archeological site in Matsusaka City, Mie Prefecture, preserves the remains of ancient paddy fields and dwellings from the early Yayoi period (ca. 300 BCE-250 CE). To reveal the cropping practices from the early Yayoi to the Middle Ages (5th-15th centuries CE), we sampled three soils there. A paddy soil from the early Yayoi had a gley horizon of silty clay loam or silty loam with a pH of 5.17-5.39. The levels of exchangeable cations, and available silicic acid were not different from those of the top layer, although the level of available P was low. An upland soil from the early Yayoi was black and had a weak blocky structure, and the contents of total carbon and nitrogen were high. A paddy soil from the Middle Ages (as well as the upland soil) had higher levels of exchangeable Ca and Mg and of available P than in a modern paddy soil.

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