Impact of Long-term Cover Crop Species Management on the Fate and Transport of Phosphorus in Regenerative Rotational Agricultural System

Increased phosphorus (P) loading from agricultural land has persistently been a major cause of eutrophication in many North American lakes. Cover crops (CC) improve soil health, increase soil organic matter, and effectively minimize total P losses via reduction of erosion and run-off from row crop agricultural fields but their efficacy regarding dissolved reactive phosphorus (DRP) loss has been contrasting and inconsistent in literature. The following studies were designed to gain in-depth understanding of the impact of long-term management of different CC species on soil P sorption and desorption, distribution, release, and loss in a Mollisol. The experimental site is a poorly drained silty clay loam soil with CC treatments consisting of cereal rye, Secale cereal L. (CR), annual ryegrass Lolium multiflorum (AR), oats / radish, Raphanus sativus L/Avena sativa (OR) grown in the same plots for 9 years and a control (CN) in a corn-soybean rotation. Results from these studies showed that long-term CC significantly decreased P sorption maximum but increased binding energy at 0 – 2 and 2 – 4 cm soil depths. Annual ryegrass significantly decreased soil WEP, M3P, and DPS relative to OR and CN at 0 – 2 cm depth. Annual ryegrass and CR significantly decreased DRP desorption by an average of 42 and 45% relative to CN and OR respectively at 0 – 2 cm soil depth. Data from the sequential chemical fractionation showed that OR and CR increased the labile P fraction by 1.5 times more than CN, but AR decrease this P fraction by 1.4 times less than the CN suggesting that AR assimilates less P into biomass thus returning less P into the soil P runoff interaction zone. Additionally, CR decreased the moderately and non-labile inorganic P pool by lowering soil pH leading to the dissolution of Ca bound phosphates. Furthermore, to investigate the impact of CC species tenure on the STP and WEP released from residue decomposition over time, an aerobic incubation was performed, and samples were collected and analyzed at 0, 12, 30, 54, 84 and 112 days. Incubation results demonstrated that M3P consistently decreased by over 40 and 50 % in long-term AR and CR respectively and increased by over 16% relative to CN.

The WEP concentration decreased by > 20 % in long-term CR and AR and increased by >80% in long-term OR going from 54 to 84 days. All treatments in the short-term management were comparable to CN suggesting the dominance of legacy P effect. This study revealed that all CC species are not created equal. The consistent trend in my results demonstrates that in areas sensitive to DRP loss, farmers should make more restrictive selection of CC species to effectively decrease DRP loading to surrounding watersheds and the Maumee River watershed.