Soil improvement - Dojo Kairyo

It refers to adding organic or inorganic materials to the soil, which is the basis of crop production, to improve the physical, chemical, and biological properties of the soil so as to improve the growth and yield of cultivated crops. Physical improvements include soil swelling and softening, improving water retention and permeability, promoting the formation of aggregates, removing gravel, and preventing water leakage, while chemical improvements include correcting the soil pH, mitigating phosphate fixation, balancing nutrients, and increasing fertilizer retention. Biological improvements include enriching useful microorganisms, promoting the humification of organic matter, and suppressing harmful microorganisms such as pests and diseases. According to the Basic Survey on Soil Fertility Conservation (1959-1978), about 40% of paddy fields and about 70% of normal fields are poor soils that are candidates for soil improvement, such as acidic soil, poor volcanic ash soil, peat soil, heavy clay, soil with excessive humus, sandy soil, gravelly soil, soil containing harmful substances, and soil lacking trace elements.

[Yuki Koyama]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

作物生産の基礎である土壌に有機質あるいは無機質の資材を投入し、栽培作物の生育収量がよくなるように土壌の物理的・化学的および生物的な性質を改善することをいう。物理性の改善には土壌の膨軟化、保水性、透水性の改善、団粒形成促進、礫(れき)の除去、漏水防止などがあり、化学性の改善には土壌pHの矯正、リン酸固定の緩和、養分バランス、保肥力の増大などがある。生物性の改善には有用微生物の富化、有機物の腐熟促進、病虫害など有害微生物の抑制などがある。地力保全基本調査（1959～1978）では水田の約4割、普通畑の約7割が土壌改良の対象となる酸性土、不良火山灰土、泥炭土、重粘土、腐植過多土、砂質土、礫質土、有害成分含有土、微量元素欠乏土などの不良土である。

［小山雄生］

出典　小学館　日本大百科全書(ニッポニカ)日本大百科全書(ニッポニカ)について　情報 | 凡例