Conversion of Conservation Tillage to Rotational Tillage to Reduce Phosphorus Losses during Snowmelt Runoff in the Canadian Prairies

Abstract

In a preceding study, converting conventional tillage (ConvT) to conservation tillage (ConsT) was reported to decrease nitrogen (N) but to increase phosphorus (P) losses during snowmelt runoff. A field-scale study was conducted from 2004 to 2012 to determine if conversion of ConsT to rotational tillage (RotaT), where conservation tillage was interrupted by a fall tillage pass every other year, could effectively reduce P losses compared with ConsT. The RotaT study was conducted on long-term paired watersheds established in 1993. The ConvT field in the pair has remained under ConvT practice since 1993, whereas tillage was minimized on the ConsT field from 1997 until 2007. In fall 2007, RotaT was introduced to the ConsT field, and heavy-duty cultivator passes were conducted in the late fall of years 2007, 2009, and 2011. Runoff volume and nutrient content were monitored at the edge of the two fields, and soil and crop residue samples were taken in each field. Greater soil Olsen P and more P released from crop residue are likely the reasons for the increased P losses in the ConsT treatment (2004-2007) relative to the ConvT treatment (2004-2007). Analysis of covariance indicated that, compared with ConsT (2004-2007), RotaT (2008-2012) increased the concentrations of dissolved organic carbon (DOC) by 62%, total dissolved N (TDN) by 190%, and total N (TN) by 272% and increased the loads of DOC by 34%, TDN by 34%, and TN by 60%. However, RotaT (2008-2012) decreased soil test P in surface soil, P released from crop residue, and duration of runoff compared with ConsT (2004-2007) and thus decreased the concentrations of total dissolved P (TDP) by 46% and total P (TP) by 38% and decreased the loads of TDP by 56% and TP by 42%. In the Canadian Prairies, where P is a major environmental concern compared with N, RotaT was demonstrated to be an effective practice to reduce P losses compared with ConsT.

Measuring the Contribution of Agricultural Conservation Practices to Observed Trends and Recent Condition in Water Quality Indicators in Ohio, USA

“…However, the weak response of phosphorus to BMPs over the recent timeframe begs the question of whether environmental benefits of existing BMPs related to soil conservation have reached an asymptote and clearly demonstrates the need to include dissolved phosphorus in routine monitoring to help gauge the dynamics of phosphorus loads in relation to new or existing strategies. This is especially important given that one of the strategies being explored to deal with the issue of eutrophication is to include rotational tillage (i.e., fall cultivation) on a biannual basis (Liu et al, 2014). As new strategies are adopted, prospective monitoring studies are needed to gauge their effectiveness and make sure that the environmental gains realized thus far are preserved.…”

Nutrient and Sediment Losses in Snowmelt Runoff from Perennial Forage and Annual Cropland in the Canadian Prairies

“…Residue extracts were analyzed for TDN and TDP at Fisheries and Oceans Canada's Freshwater Institute Laboratory, using the same methods as those described above for the runoff water samples. Release of TDN and TDP by crop residue after the freeze–thaw cycle was calculated and reported on a kilogram per hectare basis (Liu et al, 2014). …”

No-tillage controls on runoff: A meta-analysis

“…No-tillage (NT) has been recommended for soil and water conservation, reduction in labor and energy costs as well as provision of many ecosystem services (e.g., carbon sequestration and soil biodiversity conservation) (Lal et al, 2007;Triplett and Dick, 2008). However, due to lack of soil mixing and surface application of crop residues, fertilizers, and agrochemicals, NT may increase the risk of nutrient and biocide losses in runoff (Holland, 2004;Cessna et al, 2013;Liu et al, 2014). Therefore, the effectiveness of NT in reducing runoff plays a critical role in both agricultural and environmental sustainability (Palm et al, 2014;Kirkegaard et al, 2014).…”