Light-weight nursery soil has been partially adopted in Hokkaido, Japan, for use in the sugar beet paper pot transplanting system. The nursery soil for sugar beet normally comprises mineral soil, ground rice chaffs moistened with water, and fertilizer. We investigated the effect of rice chaffs in nursery soil on the quality of paper pots after growing sugar beet seedlings, which should be strong enough for transplanting. The nursery soil containing rice chaffs comprised half alluvial soil, half ground rice chaffs with 15％ (v/v) water, and fertilizer. Nursery soil with only the alluvial soil and same fertilizer and without rice chaffs was used as control.

1) After mixing, the nursery soils were incubated in a plastic bag for 50 days at 25°C. The paper pots were filled with the incubated soils and subsequently incubated at 25°C for 20 days with or without sugar beet seedlings. After incubating the paper pots, the paper quality of each pot was determined. The paper pots with nursery soil containing rice chaffs showed significantly lesser weight reduction, caused by microbial decomposition, and higher paper strength than the control nursery soil. However, the cellulase activity of the nursery soil containing rice chaffs was not significantly different from the control nursery soil.

For further investigation, the soil samples were obtained from either close to or further away from the paper. The soil placed close to the paper had a higher cellulase activity in the control nursery soil than in the nursery soil containing rice chaffs, suggesting that the localized higher cellulase activity induced a higher decomposition in the control nursery soil.

2) The nursery soil containing rice chaffs had lower NO₃–N concentrations than the control nursery soil, suggesting that the decomposition of rice chaffs induced nitrogen competition among the microbial community.

3) Microbial carbon utilization patterns were investigated using the Biolog EcoPlate (Biolog, USA). The microbial diversity was higher in the nursery soil containing rice chaffs than in the control nursery soil. Further, the carbon utilization pattern detected using the EcoPlate showed that the presence of paper and seedling roots drastically changed the microbial community structure in the control nursery soil, but not in the nursery soil containing rice chaffs, suggesting that the microbial structure in the nursery soil containing rice chaffs was stable.

4) Because mixing of nursery soil with rice chaffs made the microbial community structure compete for nitrogen and become more stable, the localized enhancement of cellulase activity in the soil close to the paper was not induced.

We conducted field and incubation experiments to investigate the emission of nitrous oxide (N₂O) from soil following the application of three types of pelleted cattle manure compost: ordinary pelleted compost, urea-mixed pellets [UP: urea (20％) and compost by fresh weight (80％)], and lime nitrogen (CaCN₂) and urea-mixed pellets (LNUP: 1％ lime nitrogen by fresh weight of UP). Our goal was to develop techniques to decrease N₂O emission from the pelleted manure compost applied to the fields and to utilize these pelleted composts as compost mixed fertilizer in crop production.

1) In both field and incubation experiments, cumulative N₂O emission per unit of nitrogen applied was significantly lower with UP than with ordinary pelleted manure compost applications. A large N₂O emission peak was observed at 1–5 days after the application of ordinary pelleted manure compost, but not when UP was applied.

2) In both field and incubation experiments, cumulative N₂O emission per unit of nitrogen applied was lower with LNUP than with UP applications. In the incubation experiment, N₂O emission, which was likely derived from nitrification, from day 5 to day 19 was lower with LNUP than with UP applications.

3) In the field experiment, the dry weight of komatsuna (Brassica rapa var. perviridis) plants per unit area in plots fertilized with UP or LNUP did not differ significantly from the plots fertilized with urea (a widely used nitrogenous fertilizer) when the same amount of nitrogen was applied.

‘Hoshimaru’ is an early variety of direct-seeded rice (Oryza sativa L.) suitable for the Hokkaido region, and it is necessary that it absorbs 100 kg ha⁻¹ nitrogen (N) by maturity to obtain 5.0 Mg ha−1 grain yield. It is necessary to determine the timing and amount of N top-dressing to prevent lodging and to obtain the required grain yield, a high grain quality, and a good eating quality. Nutrition diagnosis using plant growth and leaf color was investigated to determine the need and limit of N top-dressing.

1) A close relation was found between the multiplied value of plant length and tiller number (P×T value) and N-uptake rate at the panicle formation stage (PFS).

2) A close relation was also found between N-uptake rate at the heading and the multiplied value of leaf color value and tiller number (L×T value) at PFS, irrespective of the experimental year.

3) A close relation was also found between the number of grains per unit area or brown rice yield and L×T value at PFS. Therefore, L×T value at PFS is a good index to regulate N uptake. Considering the effect of N top-dressing at PFS in each L×T value, the diagnostic criterion was decided. When L×T value at PFS was less than 32,000, N top-dressing at PFS was needed. When L×T value was more than 32,000 at PFS, further N application was not needed.

4) When L×T value at PFS was less than 32,000, 20 kg ha⁻¹ of N top-dressing at PFS improved the rice grain yield with a high grain quality and a good eating quality in brown lowland soil.

5) The rate of protein content of milled grains was higher in the peat soil and gray lowland soil than in the brown lowland soil.