Fertilizing grass with a mechanical cow


by Troy Bishopp

Nowadays many farmers are rolling down growing cover crops and plowing under sod as green manures for a corn crop. The traditional rotation practice adds nutrients and organic matter benefits to the next crop. It wouldn’t be a stretch to figure mowing or trampling down a pasture crop could help fertilize itself also.

This makes some sense since my animal numbers didn’t match the explosive growth of May.

What to do with all the “seedheads” and excess pasture has been a hot topic on many social media platforms and group chats. The typical banter is to cut it for hay, put on more animals to eat it down (not so easy), do some form of adaptive mob-grazing and/or clip pastures before or after the ruminants’ graze period. Recipes and commentary abound with little context for individual farm goals, tools, experience and the price of high input costs. Consider what your best options are – they should be holistically vetted given our current parameters.

For many farmers without the scale, resources or desire to make winter feed from their pastures in this environment of high costs, the thought process can be daunting as the plants mature and feed quality dwindles. Maybe all this grass has a silver lining. We should consider this a good problem to have, given our Western counterparts have little moisture or pasture and have sold their animals.

An enterprising alternative, back in 1955, was used by farmer/author Newman Turner, who wrote about his experiences in “Making a Ley with a Mower” as a chapter in his book, “Fertility Pastures and Cover Crops.” Turner wrote, “In my experience the only essential is organic matter. The use of adequate organic manure (crop residue) and animal wastes will, on all soils, ensure the release of all other requirements of the ‘ley’ – pasture. Organic nitrogen, phosphates, potash, even calcium in small but usually adequate quantities are supplied in the process of decomposition of organic matter.”

He continued, “The orthodox reason for topping (mowing) after grazing is to stop the seeding stems and encourage fresh, leafy growth. But I soon discovered the benefits resulting from the mowing after grazing consisted of deep rooting herbs and a diversity of plant herbage supplying a rich supply of subsoil minerals, trace elements, plant hormones, mycelia, fungi and who knows what, contributing free fertilizer back on itself. I found in this way that I could maintain, entirely by utilizing free natural processes, the high production of the pasture.”

His premise and study didn’t really sit well with fertilizer salesmen and his own “Ministry of Agriculture experts.” The frugal farmer was more concerned about thriving from their homegrown, productive, diverse pastures than making friends from industry (a sentiment that could be realized in today’s farming environment perhaps).

Fertilizing grass with more grass may make sense in the age of high inputs. Photo by Troy Bishopp

There is a bevy of information of how many nutrients are extracted from forage harvesting per ton. Many university bulletins give a range of $40 to $60 worth of NPK in a ton of hay harvested as an example. What if we looked at this as fertilizer instead of cow feed only?

This is what I think about as I ride my mechanical Deutz cow with Woods mower in tow, emulating Mr. Turner’s teachings and pruning my barely grazed pastures. This ain’t no vanity mowing. This is fertilizing pastures.

I reached out to several agronomy professionals for a hypothetical look on what I may be achieving. According to my pasture sward measurements, I am mowing down one to 1.5 dry matter tons/acre (20 inches x 150 lbs./inch/acre) after the 50 beef finishers took their grass cream off the paddock.

Some said the greener the material, the more nitrogen potential (catalog.extension.oregonstate.edu/sites/catalog/files/project/pdf/pnw636.pdf). All said, it takes time for material to break down and provide its slow-release fertilizer so the benefits aren’t immediate, like other sources of fertility. There were many intangibles from mowing, such as weed suppression, covering the soil, encouraging new growth, feeding the biological community, providing a natural seedbank and creating organic matter on the soil plus roots sloughing off the plants under the soil.

The fertilizer value of bush-hogged pasture was said to “depend” on what stage of pasture maturity was getting mowed. Apparently, the older the plants, the less nutrients applied. After much discussion, a 10-10-45 fertilizer ratio on a dry matter basis was agreed upon. Given that today’s prices are over $1/lb. for nitrogen and phosphorus, and 60 cents/lb. for potassium, a hypothetic value of this mowed fertilizer is somewhere in the neighborhood of $50/acre. Not bad if you have excess grass to invest in your soil and don’t have enough cows to eat or trample it down.

Of course, mechanical cows don’t run for free (or horse-drawn iron, for that matter). I personally bill the mowing operation out at $90/hour these days to account for the increased fuel, maintenance and labor costs. I’m keeping track on my grazing chart how long it takes me to mow a field off behind the cows. Typically, I can mow four acres of heavy pasture down to six inches in 1.5 hours with my seven-foot bush-hog and sharp blades. The math plays out in my head: 4 acres x $50/acre = $200. Then $90/acre x 1.5 hours = $135 for a positive return of $16/acre for doing the practice that Mr. Turner discussed. Is it enough benefit to use Mr. Turner’s idea? You’ll have to judge based on your own considerations.

This idea has some merit to consider especially as outside inputs become more expensive or even scarce. It’s just one tool in a vast toolbox of possibilities for this short-term excess pasture issue some folks are experiencing. However, the ultimate pasture scenario is to have every blade harvested by an appreciating grazing animal to be truly sustainable. Don’t beat yourself up if you have a few too many seedheads.  Finding the triple bottom line balance is always a moving target. Invest in knowledge – you won’t be sorry.

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