Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/29/2007
Publication Date: 7/1/2008
Citation: Allen, B.L., Mallarino, A.P. 2008. Effect of liquid swine manure rate, incorporation, and timing of simulated rainfall on phosphorus loss with surface runoff. Journal of Environmental Quality. 37:125-137.
Interpretive Summary: Swine manure often is applied to soil as a source of crop nutrients, including phosphorus (P). However, excessive P application can lead to surface water quality impairment. This outdoor rainfall simulation study was conducted in Iowa to measure P forms in surface runoff following different rates of liquid swine manure application, incorporation into the soil, and timing of runoff events. Phosphorus in runoff within 24 hours of applying manure without incorporation increased linearly or exponentially with increasing manure application rates. Incorporating the manure resulted in both significantly lower runoff P and the proportion of P forms considered most detrimental to surface water quality. Delaying rainfall 10 days following manure application without incorporation sharply decreased runoff P compared to runoff within 24 hours. Delaying rainfall 6 months reduced runoff P even further. Even a short delay in runoff-causing rainfall sharply decreases the risk of P loss following surface-applied liquid swine manure. Manure incorporation with tillage reduces P loss for runoff events immediately after application but not necessarily after 10 days. There is a need for considering probability of runoff-causing rainfall when addressing risk of P loss from surface-applied liquid swine manure.
Technical Abstract: Excessive manure P application increases risk of P loss from fields. This study assessed total (TPR), bioavailable (BAP), and dissolved reactive (DRP) P concentrations and loads in surface runoff following liquid swine (Sus scrofa domesticus) manure application with or without incorporation into soil and different timing of rainfall. Four replicated manure P treatments were applied in 2002 and again in 2003 to two Iowa soils testing low in P managed with corn (Zea mays L.) - soybean [Glycine max (L.) Men.] rotations. Total P applied each time was 0-80 kg P ha-' at one site and 0-108 kg P ha-' at the other. Simulated rainfall was applied within 24 h of P application or after 10-16 d and 5-6 mo. Nonincorporated manure P increased DRP, BAP, and TPR concentrations and loads linearly or exponentially for 24-h and 10-16-d runoff events. On average for the 24-h events, DRP, BAP, and TPR concentrations were 5.4,4.7, and 2.2 times higher, respectively, for non-incorporated manure than for incorporated manure; P loads were 3.8,7.7, and 3.6 times higher; and DRP and BAP concentrations were 54% of TPR for non-incorporated manure and 22-25% for incorporated manure. A 10-16 d rainfall delay resulted in DRP, BAP, and TPR concentrations 3.1,2.7, and 1.1 times lower, respectively, than for 24-h events, across all non-incorporated P rates, sites, and years; while runoff P loads were 3.8, 3.6, and 1.6 times lower, respectively. A 5- to 6-mo simulated rainfall delay reduced runoff P to levels similar to control plots. Incorporating swine manure when the probability of immediate rainfall is high reduces the risk of P loss in surface runoff; however, this benefit sharply decreases with time. Abbreviations: BAP, bioavailable P; DRP, dissolved reactive P; OM, organic matter; STP, soil-test P; TPR, total runoff P; TPS, total soil P.