Effects of Manure Application on Runoff and Erosion
There are added benefits to manure as compared to fertilizer application. Manure application often reduces runoff and erosion. Manure application often amends the soil to have better water infiltration. Finally, soil aggregation also may be improved to have more soil in water-stable macro-aggregates and to make the soil less vulnerable to raindrop splash and other erosive forces. These effects can persist for several years. During three years of composted manure application in eastern Nebraska, runoff and sediment loss were one-half to one-third less on soils where manure was applied, as compared to where no manure was applied.
Figure 7. Composted manure application resulted in less loss of sediment during 3 years of annual application, and during 4 years following application (t/ac = 2.24 Mg/ha). (Graph by Charles Wortmann)
Figure 8. Composted manure application resulted in less runoff during 3 years of annual application and during 4 years following application (acre-inch, ac-in=103 cubic meters). (Graph by Charles Wortmann)
This amendment effect persisted for at least four years after the last application, during which time runoff and sediment loss with manure applied were 60% and 45%, respectively, of the losses where no manure was previously applied. While manure application does not always result in reduced runoff and erosion, the effect is common enough to be considered as partly offsetting the effect of increased runoff P concentration following manure application. P losses were greater where repeated compost application resulted in greater increased soil test P, but the increased P losses were less than might be expected due to reduced runoff and erosion with compost applied (Fig 9).
Figure 9. During the years following application of composted manure, bio-available P loss was greater with compost application, but the increase was small, given that soil test P was 16, 380, and 780 ppm in the top 2' of soil for the no-compost, low-P-compost, and high-P-compost treatments, respectively (lb/ac = 1.12 kg/ha). (Graph by Charles Wortmann)
Discussion Question: How long is the amendment effect of manure application likely to persist?
Answer: We do not have good information for making such an estimate. However, four years after the last application of composted manure, the compost treated plots had 20% more soil in water stable macro-aggregates (> 0.25 mm) than where no compost was applied.
Discussion Question: Bio-available P loss increased more than sediment P loss with increasing STP. The plots in this study are approximately 35 feet long, and the slope length is too short for the runoff to have much erosive power. If this were at a field scale with slopes of > 100 feet, which treatment is likely to have the greatest increase in sediment P loss?
Answer: Probably the no compost treatment with STP of 16 ppm as it is likely to have greater runoff, and more erosion, than where compost was applied.