Data from: Surface and subsurface phosphorus discharge from a clay soil in a 9-year study comparing no-till and plowing

No-till as a water protection measure is highly efficient in controlling erosion and particulate phosphorus (PP) loss, but tends to increase dissolved reactive P (DRP) concentrations in runoff water. In a 9-year field study on a clay soil in SW Finland, the effects of no-till and autumn plowing on surface runoff and subsurface drainage water quality were compared. The site had 2% slope and was under spring cereal cropping, with approximately replacement fertilizer P rates. Vertical stratification of soil test P that had developed during a preceding 6-year grass ley was undone by plowing, but continued to develop under no-till. During the 9-yr study period, no-till soil had 27% lower cumulative total P losses than plowed soil (10.0 vs. 13.7 kg TP ha-1). Concentrations and losses of PP were clearly lower under no-till than plowing (5.6 vs. 12.3 kg PP ha-1), but DRP loss showed the opposite trend (4.3 vs. 1.4 kg DRP ha-1). There was an increasing trend in subsurface drainflow DRP concentration under no-till, possibly because of development of a conductive pore structure from soil surface to drain depth. The potential benefit of no-till in water protection depends on how much of the PP transported to water is transformed into a bioavailable form and used by aquatic organisms. The beneficial effect of no-till in controlling P induced eutrophication at the study site would only be realized if the bioavailable share of PP exceeds 43%. Otherwise no-till would not be an efficient eutrophication control measure at this site.免耕（no-till）作为水体保护措施，在调控土壤侵蚀与颗粒态磷（particulate phosphorus, PP）流失方面成效显著，但往往会提升径流水中的溶解态活性磷（dissolved reactive phosphorus, DRP）浓度。本研究针对芬兰西南部的黏质土壤开展了为期9年的田间试验，对比了免耕与秋翻两种耕作方式对地表径流及地下排水水质的影响。试验地块坡度为2%，种植春季谷类作物，施肥量维持磷素平衡（即等量磷补充施肥率）。此前6年人工牧草种植期形成的土壤有效磷垂直分层，经秋翻后被彻底破除，而免耕处理下该分层则持续发育。在9年试验周期内，免耕土壤的累积总磷（total phosphorus, TP）流失量较翻耕土壤低27%（分别为10.0与13.7 kg·ha⁻¹）。免耕处理下PP的浓度与流失量均显著低于翻耕处理（5.6与12.3 kg·ha⁻¹），但DRP流失量则呈现相反趋势（4.3与1.4 kg·ha⁻¹）。免耕处理下地下排水径流的DRP浓度呈上升态势，这可能源于土壤表层至排水层之间形成了导水孔隙结构。免耕在水体保护方面的潜在效益，取决于输送至水体的PP中有多大比例会转化为生物可利用形态并被水生生物利用。在本试验地块中，仅当PP的生物有效占比超过43%时，免耕控制磷诱导富营养化的有益效应才能得以实现；反之，免耕在该地块并非高效的富营养化防控措施。