Change Needed in Applying Fertilizer to Perennial Grassland

In a January-February 2006, Journal of Soil and Water Conservation article, Incorporating Granular Inorganic Fertilizer into Perennial Grassland Soils to Improve Water Quality, D.H. Pote and other researchers recommend incorporating fertilizer into the soil versus the common practice of applying fertilizer on the surface of grass and rangeland. Beef and dairy producers need forage to feed their livestock and they often apply inorganic fertilizers on pastureland to increase forage growth.

Pote and his fellow researchers re-emphasized that the more common manner of distributing the fertilizer-spreading granules on the surface leaves the fertilizer vulnerable to runoff and loss into the atmosphere as ammonia.

They hypothesized that a knifing technique gets the fertilizer closer to the roots and minimize the two negative impacts of having the fertilizer laying on the ground’s surface. To look at the effect knifing-in the fertilizer, Pote et al. studied the yield and runoff water quality on plots with eight to ten percent slope of silt loam soil with well-established bermudagrass. They favored knifing the soil and spreading the 13-13-13-fertilizer over the top as an attractive option since current equipment could achieve the cuts and spreading-with-knifing to move the fertilizer down into the cuts.  The cuts were made every eight inches across the plot and three inches deep. The plots had simulated and natural rainfall throughout the study.

The researchers found that even though knifing the soil and spreading the fertilizer over the top was easy to apply and slowed runoff, it did not provide the best safety for fertilizer being carried. The yield from this method was not negatively impacted by cutting the soil and spreading over the top, but yield was not significantly improved either unless the fertilizer is incorporated into the soil. Incorporating the fertilizer into the soil also was the optimum in water quality of runoff. On plots where the fertilizer was incorporated, the nutrient concentrations and loads in runoff were decreased by 90 percent.

Pote et al. also found that both yield and runoff water quality were improved when fertilizer is incorporated into the soil. This meant that field equipment currently under development to mechanize this process is needed now.  Ultimately, the easier process of cutting and spreading on top of the pastureland did not prove worthwhile.
Your contact is Deb Happe, Soil and Water Conservation Society, at 515-289-2331, ext. 26.