Surface and Subsurface Phosphorus Discharge from a Clay Soil in a Nine‐Year Study Comparing No‐Till and Plowing

Abstract

No‐till as a water protection measure is highly efficient in controlling erosion and particulate P (PP) loss but tends to increase dissolved reactive P (DRP) concentrations in runoff water. In a 9‐yr field study on a clay soil in Southwest Finland, the effects of no‐till and autumn plowing on surface runoff and subsurface drainage water quality were compared. The site had a 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‐yr 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 total P ha−1). Concentrations and losses of PP were clearly lower under no‐till than under 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. Core Ideas No‐till decreased total P losses by 27% compared with autumn plowing. No‐till produced 4.5‐fold higher DRP loss and 54% lower PP loss than plowing. When changes in DRP and PP are opposite, TP changes should be interpreted with caution. In this case, the effect on eutrophication largely depends on PP bioavailability. At the study site, increased DRP load is compensated if PP bioavailability is >43%.

A Global Perspective on Integrated Strategies to Manage Soil Phosphorus Status for Eutrophication Control without Limiting Land Productivity

“…Lower SRP concentrations recorded in flow through field drains under natural rainfall in the United Kingdom are also in line with previous studies (Haygarth et al, 1998; Withers et al, 2009b), although this trend was not observed under Finnish conditions. This may be due to the more strongly structured clay soils in Finland, where rapid flow along cracks and biopores decreases the contact time between percolating water and subsoil (Uusitalo et al, 2018). …”

Increasing the Effectiveness and Adoption of Agricultural Phosphorus Management Strategies to Minimize Water Quality Impairment

“…A meta‐analysis comparing P losses of conservation versus conventional tillage demonstrated a 40% increase in both SRP concentration and load due to conservation tillage, although the amount varied based on rainfall (Daryanto et al, 2017). Other studies have demonstrated SRP increases from land under conservation tillage (Dodd and Sharpley, 2016; Jarvie et al, 2017; Renwick et al, 2018; Uusitalo et al, 2018). The increase in SRP with conservation tillage was relative to the reduction in sediment‐attached P, which may actually increase degradation of water quality since SRP is more bioavailable.…”

“…Dodd and Sharpley (2016) noted a range for particulate P reduction due to conservation tillage from −33 to 96% compared with 45 to 89% for grassed waterways. Following 9 yr of research on a clay soil in Finland, Uusitalo et al (2018) demonstrated that particulate P loads and concentrations were 27 and 55% lower, respectively, with no‐till than with conventional till.…”

Variations in near-saturated hydraulic conductivity of arable mineral topsoils in south-western and central-eastern Finland

“…The effect of tillage on near-saturated K(h) was examined in Kotkanoja leaching field at Jokioinen (Turtola et al 2007). The soil at the field site is classified as a Protovertic Luvisol (Clayic, Cutanic) and its topsoil clay content ranges from 50 to 60 % (Uusitalo et al 2018). The measurements reported here were performed in summer 2017 and 2018 in a no-till plot (KO B) and a ploughed plot (KO C) (Table S1).…”

“…Plot KO C is autumn-ploughed annually and harrowed in May for seedbed preparation. Full details of the management regime for the Kotkanoja field can be found in Uusitalo et al (2018). Measurements were performed four times (with four replicates) in both 2017 and 2018 except in plot KO C, which was ploughed on the last measurement occasion in 2018.…”