Reprinted from On Pasture.
We have so far only considered the role of buying and feeding hay as a Nitrogen source for your pastures. Hay is also a great source for slow-release Phosphorus to benefit your pastures.
Manufactured P fertilizers have recently been shown to be detrimental to the presence and function of beneficial mycorrhizal fungi in the soil. Using fed hay as a P source rather than concentrated soluble fertilizers feeds the fungi rather than diminishing them.
Factors Limiting Plant Growth
Nitrogen is generally considered to be the first most limiting nutrient for plant growth in terrestrial environments. Phosphorus is very often the 2nd most limiting nutrient. Unlike the N fixation process carried out by legumes in association with Rhizobia bacteria, we cannot create P out of thin air.
P is critical to both plants and animals as all energy transfers within plant and animal are mediated by P containing compounds. Abundant P is necessary to have healthy pastures and livestock.
Almost all P excreted by animals is in the dung. Because most cattle defecations occur when the animal is at rest, dung tends to accumulate where animals congregate – on the feeding line for example, or where cattle bed in hay not consumed. It does not get spread out over the entire pasture area if feeding is limited to small areas of the pasture.
This why spreading the hay out in the feeding process helps the P cycle.
Excess Nutrients Cause Problems
While P is a critical component of life, it also has pollution potential if we are allowing manure to concentrate in areas prone to surface runoff and soil erosion.
Mismanaged hay feeding can lead to excessive runoff of fecal material into surface water leading to aquatic weed growth and algal blooms. The ‘dead zone’ in the Gulf of Mexico and Chesapeake Bay are due to P runoff as well as N runoff.
How Much P Does Hay Feeding Provide?
Using our previous example of bale grazing with over 20 tons of hay/acre fed, the P load would be about 80 lbs/acre. That is not an excessive amount of P, although the N load was quite high.
Since that P is almost all contained in dung pats, it is slowly released back to the soil through microbial decomposition processes. The greater the biological and insect activity in the soil, the quicker the release process.
We only have a possibility of P contamination of surface waters when there is actual water runoff and/or soil erosion taking fecal particles and soil to the riparian areas.
The key to minimizing risk of P pollution from hay feeding is keeping the feeding areas well away from surface water.
Let’s keep them high & dry!