Our lawn is not crop land. There is no net removal of plant mass as we typically mulch mow lawn and donít keep goat to graze our lawn today. I can smell strong ammonia from grass clipping compost, so much N is expected to return to soil by micros. Yes, some N can leach out of soil, but so can K which is even more mobile than N. So why is lawn fertilizer, 22,0,4 or 25,24,4, is disproportionally high in N and low in K?
N is very mobile, P and K are much less mobile (K is way less mobile in soils than N, youíve got that backwards).
There is more that just one way to lose N, itís not just to leaching. Volatilization and denitrification are big contributors to the Nitrogen cycle (aquaria version of the N cycle is only part of the entire N cycle). Plant uptake is another large contributor to N removal from the soil.
When you can smell ammonia from the clippings, that smell is volatilization occurring. For a different example, spreading manure on top of a field, in warm weather, can induce 100% free nitrogen loss.
Iíve seen soil samples from lawns, and they are insanely high in N, P and K. But, the N is not at high in proportion to the P and K. If you spread a higher P and K fert for a few seasons, your soil levels will be very, very high because there is little loss (unless you are bagging clippings, then there is a lot of removal).
N is a different story, after a large snow melt each year, or the downpours of the rainy season in warmer climates, N loss can be very high, meaning we still need to fertilize N. Sulphur is the same, sulphate is prone to leaching much the same as nitrate, and we arenít getting the Sulphur deposits like we used to do to coal plants becoming a thing of the past, so we should be fertilizing sulphur at a 10:1 (ish) ratio of N:S.
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