In Hokkaido, the planted area and production of potatoes for processing are increasing. The fertility of phosphates, which aids in the early growth of crops, is deemed crucial in upland fields where Andosols are widely distributed. Despite the increase in fertilization, no studies have confirmed the reduction of phosphate fertilizer. Hence, we carried out field experiments on the reduction and application rate of phosphate fertilizer at growers’ fields where processing potatoes were grown to explore the potential for fertilizer reduction. Experiments were conducted in the Tokachi and Kamikawa districts at growers’ fields, where the phosphate fertilizer applied was half the standard rate, and the amount varied between 0 and 250 kg-P₂O₅ ha⁻¹. Comprehensive cultivation experiments were also performed at the experimental fields of Obihiro University of Agriculture and Veterinary Medicine, where the phosphate fertilizer applied was halved. The results of these experiments showed that the halved fertilizer plots yielded equal or higher than the standard plot, irrespective of the region or year. The application rate experiments revealed that the amount of phosphate fertilizer applied did not influence the yield of processing potatoes and that applying fertilizers beyond the standard fertilization rate decreased yield. To maintain yield levels and phosphorus fertility, it is advisable to apply phosphate fertilizer at a rate of 50 to 100 kg-P₂O₅ ha⁻¹. In comprehensive experiments, reduced fertilization plots with a 50％ fertilization rate yielded equal or higher yields than those in standard plots. It is essential to challenge the outdated notion that “phosphorus deficiency is a problem for crop production in Andosols fields” and update our understanding of soil science.

The recent expansion of neglected bamboo forests poses a risk of increased crop damage by wild animals, necessitating the use of bamboo resources, such as bamboo powder, for soil amendment to manage these forests effectively. The rice cultivar “Yudai21,” which is increasingly being planted, exhibits spindly growth in nitrogen (N)-rich soils. However, the amendment of bamboo powder, with its high C:N ratio, is anticipated to inhibit this growth. Our study aimed to analyze the effects of mixing bamboo powder with nursery box soil on the growth and yield of paddy rice, thereby assessing the utility of bamboo powder. We used fertilized soil and forest subsurface soil with varying ratios of bamboo powder (0％, 30％, 60％ by volume) to compare the effects of bamboo powder mixing on seedling growth and rice yields under both conventional and organic farming practices. Our findings suggest that mixing bamboo powder with nursery box soil offers several benefits for growing Yudai21, including inhibiting spindly growth of rice seedlings (especially in fertilized soil), increasing seedling-mat strength, and reducing the weight of nursery box soil. Growing seedlings in nursery box soils mixed with bamboo powder did not negatively impact rice yields under either farming practice. However, we also observed that a high dose of bamboo powder (60％) led to uneven seedling emergence and a decrease in leaf chlorophyll (SPAD value) due to nutrient deficiency. These results suggest that the optimal ratio of bamboo powder to mix with nursery box soil is around 30％ under the studied soil conditions.

A pot experiment was conducted to determine the optimal conditions for applying the herbicide (glyphosate) to grassland seedbeds on peat soil. Subsequently, field-scale tests were conducted to validate the results from the pot experiments and assess the herbicide’s effects on actual peat meadows. Another pot experiment indicated that waterlogging did not exacerbate chemical injury, and plant establishment was not disrupted by chemical injury when the soil ignition residue exceeded 0.55 kg kg⁻¹. A survey of peat fields with soil ignition residues ranging from 0.54 to 0.76 kg kg⁻¹ revealed that glyphosate application on seedbeds did not affect timothy populations before winter. The following spring, timothy crown cover ranged from 75％ to 90％, and the first cut yield component was high (88–93％). In another survey, peat fields renovated with cocksfoot and perennial ryegrass were investigated to evaluate the effects of seedbed treatments. Treated plots showed sufficient grass stems before winter and low weed crown coverage in following spring, while untreated plots were invaded by weeds that suppressed the grass. These results highlight the high applicability and effectiveness of herbicide treatments on seedbeds.

Effective field drainage and wetness information is crucial for farmers to plan cultivation strategies in irrigated rice paddy and upland crop rotation areas. In this study, we developed a method to create regional and field-specific maps by assessing five classes of field drainage and wetness through unsupervised classification of three low plant coverage aerial images that were shot at different times in February in a paddy rice and upland crop rotation area (500 ha) in Chikusei City, Ibaraki Prefecture. The study area, located in Kokaigawa Lowland, exhibited substantial intrafield and interfield variations in water retention and drainage characteristics. The classification results guided a field survey, which revealed the presence of a shallow gravel layer, a dense and low-permeability plow pan, and a muck-like layer in the subsoil, all of which contributed to field drainage and wetness. A comparative analysis of the classification results and the evaluation by farmers based on their knowledge of field drainage and wetness showed broadly match. Further analysis based on three groups of the crop cultivation (bare-after paddy rice, bare-after soybean, and wheat) indicated a lower Kappa coefficient for the bare-after paddy rice group, likely due to the presence of residues and a reduced pulverization ratio in the field surface after paddy rice cultivation.