Pasture Nutrition and Foliar Spraying

Fields can be improved with proper use of foliar sprays

Pasture is defined by livestock. Grass without animals standing in it and eating it is only lawn, meadow or hayfield. It would be foolish to pretend one does not influence the other. 

But the reader will have to forgive me for not adequately addressing the animal in this article, because I’m primarily going to consider the vegetal.

Grassland and silvopasture are the world’s preeminent solar energy collectors and, in combination with grazing animals, are elegantly self-sufficient. This makes pasture gigs rather satisfying and straightforward for me as a regenerative farm consultant. Animals are an almost-guaranteed way to build soil organic matter that just tends to work out over time, fertility-wise, because: nature. 

This ease of reaching a tolerable state of success, though, can blind us from the greater possibilities. Applying techniques learned from more fertility-intensive cropping systems allows pastures to produce phenomenal amounts of protein and fat per acre. Doesn’t it behoove us to polish that shiny jewel, rather than the turd of subsidized-synthetic-GMO-monocrops as CAFO fuel? 

Few are the times I’ve heard someone plan to retire to a vegetable farm. But folks often wax bucolic on spending their later years watching grass grow. A back-porch iced-tea dream, where mild-mannered hooved beasts peacefully sort out their own needs — that suits a laissez-faire mentality that intensive fruit and veg production simply does not. 

While overly idealistic, there is something to this. Grazing animals, for all their mass and persnickety willpower, can care for themselves rather well.

Given the right opportunity, livestock gather their own food and water, defend themselves from predators and move themselves to shade. (If only plants would do these things!) As importantly, ruminants care for and directly benefit their pastures. One begets the other — a wondrous and endless fertility-creating mutualism that many writers have plumbed the romantic depths of. 

I agree. It’s true: Well-managed grazing improves soil. However, poor grazing greases the slippery slope toward desertification — so note the qualifier “well-managed.” This includes at least rotational grazing, plant diversity and constant cover. It gets better from there, with multi-species and mob grazing, higher-impact rotations with longer rest, warm/cool-season seedings, etc. 

Overlap several of these techniques, and soils WILL improve over time with very little input. Forage quality and healthy, heavy animals can’t help but follow … eventually. But don’t retire just yet, as there may be some finer points to work out while determining your tolerance for “eventually.”

It’s impossible not to oversimplify pastoral interactions between sun, plant, microbe, ruminant, manure and soil. Thankfully, this magazine has introduced ideas, authors and ranchers over the years who have addressed these myriad interconnections. Thus I will only delve into a few bits of mineral nutrition here, with an emphasis on foliar applications. 

Perhaps more than any other crop type, pasture is ready and willing to receive and use a foliar spray. There is almost always plenty of leaf to intercept the droplets, it’s in a constant vegetative state, and there is a consistent cycle of graze-rotate-spray-grow-repeat. 

There is also a broader window of application timing than with other crops. As long as grass is not clipped below 4-6 inches, applications can be made immediately after a move. Many growers use an ATV-mounted sprayer setup to foliar feed each small paddock — a practice that piggybacks nicely onto the daily chore of moving electric fence in tight, intensive-grazing rotations. Alternatively, one can allow several weeks of regrowth before spraying and use a larger ground rig to treat multiple recently grazed paddocks or a large pasture at once, on a less regular basis. 

On established pastures, I usually forgo foliar applications until after the first grazing. Winter dormancy and rapid spring mineralization routinely produces the best grass of the year. It is coming into the stressful summer and fall months that routine foliars best maintain productivity. 

Pasture “yield” is all about high-protein leaf growth, with yield tied to vegetative response. There are few complex plant events like flowering, fruiting or seed-bearing to worry about. Thus, there are fewer minerals and points of influence to micromanage. Just facilitate photosynthesis all the time. 

The most critical photosynthetic minerals are manganese, iron, magnesium, molybdenum and nitrogen. Supplied amply with these minerals, photosynthesis is limited only by sunlight and water. Lack of even one, though — in complementary balance to the others — and the entire system is hindered.

Soils vary considerably in actual quantity and availability of these elements. Traditional soil testing gives a fairly accurate view of overall availability, though a basic pH will reduce actual plant uptake of soil micronutrients significantly. 

Manganese, iron and molybdenum are vastly more effective as foliar sprays since rates are so low. Nitrogen and magnesium can be applied to either soil or leaf with good results, but increased efficiency of uptake at lower volumes are achieved with a foliar. Magnesium levels change minimally over time, while nitrogen can go through huge swings based on soil health and weather.

More nitrogen generally grows greater grass tonnage but with lower protein content and fiber. Sulfur must be present at a 1:10 ratio with nitrogen in order for nitrogen to become protein. Sulfur is almost endlessly recycled in pastures once stable levels are achieved.

Molybdenum in plants converts nitrates — a major plus — but it can be a toxicity concern for sheep and cattle. When foliar-spraying molybdenum, leave at least a few weeks between application and grazing to allow any residues to be transported and diluted throughout the plant and root system. 

Timescale and trackability are confounding on pasture. What impact has one paddock’s offerings made by the time an animal leaves the farm? For a dairy, results are almost immediate. Better pastures make more milk with higher fat and protein the very next day. For a meat operation, the keenest pasture suitability test is performed by those eating it — second best, by those watching it being eaten. Thus, good animal husbandry remains as much about observation as technical analysis: The sward is mightier than the pen.

But there are other tools to confirm or confront our suspicions. Traditional forage analysis is viable. It tracks critical metrics of digestibility and energy from an animal-nutrition perspective. It only shows an end result, though, and lacks guidance while the plant grows — when there is something to DO about it. Sap analysis is a heartier tool for understanding how practices influence plant health and growth. 

Before sap-testing pastures, consider your goals. I suggest sampling the species you hope to increase, since the information will be used to steer fertility toward that crop’s needs. I.e., if your alfalfa is dying out year by year, test it and feed accordingly. Though many plants may receive the same nutrient spray, an optimized program provides disproportionate benefit to one. Or, one might collect leaves from a representative mix of species in the sward, in order to get a broader average. This is straightforward in a pure grass stand, a trifle trickier in a mixed legume and grass paddock and quite complex in diverse fields with many species of forbs, herbs, grasses and legumes. Test what you wish to improve.

For most pastures, where plants are not allowed to get to full height, the usual sap technique of sampling both old and young leaves separately is moot. I suggest a “half-test” of young leaves only. This is what the animals primarily eat and is what we wish to affect.

The most economically relevant time to sample is midway through each growth cycle, after plants have rebounded from the last grazing and grown at least a couple of inches of new leaf. This gives time to review test results, respond with a customized application, and get adequate plant response before the next graze. 

To examine the nutrient content of a stand as it will be going into the animal, delay sampling until just prior to a graze. This provides additional mineral data not represented by dry-matter forage analysis.

Many pasture managers are concerned with phosphorus. Yet after eight years of reviewing sap analysis — which allows an inside look at what plants do with the fertility we throw at them — to me, the most striking thing about phosphorus is that plants couldn’t care less … while we humans are obsessed with it. Phosphorus fluxes in plant sap are closer to the ppm-sized shifts we observe in micronutrients — not like one of the big three macronutrients. 

Plant sap phosphorus is very closely tied to growth stage. Levels are highest in a vigorously growing young leaves (which ruminants thrive on). In older leaves that are no longer growing, phosphorus remains low. If you want to believe you are phosphorus deficient, just sample old leaves. However, providing more neither makes the old leaf grow again nor causes the new leaf to grow faster or bigger. 

Lab-grown plants with artificially missing phosphorus do suffer. But in field conditions, it is very rare for it to be a limiting factor. Conventional agronomy has overstated plant need, and most soils are capable of providing what is needed through normal plant-microbe relations. 

Phosphorus applications are warranted when biological conditions are so bad that soil life is scant or inhibited — such that inoculations don’t establish phosphorus-solubilizing bacteria or mycorrhizae, or when soils are so sandy and low in organic matter that farming is questionable anyway. Then, repeated applications of available phosphorus may be on the menu for a long time. Still, rates less than a pound of actual phosphorus per acre, delivered as a foliar during growth, are as effective as many dozens of pounds dumped on cold, wet soils. 

If your dirt is dirty, it’s got phosphorus. And pasture is an ideal phosphorus recycler. Most animal-centric systems achieve over-abundant phosphorus status within a number of years. Critters collect, concentrate and solubilize phosphorus in manure and urine. Green plants keep bacterial populations intact. Unlike a hayfield, biomass stays in the pasture, so little is exported. There is very little tillage, which allows mycorrhizae populations to thrive. Soils are covered all the time, so erosion is minimal, and phosphorus won’t wash or blow away. All these things build biologically available phosphorus. Without solid evidence that your pasture truly lacks it, don’t worry. Where availability doesn’t yet match soil reserves, phosphorus-solubilizing bacterial inoculants, plant diversity and a few months work wonders.

Nathan Harman is a once and future farmer, a father, and a consultant for Advancing Eco Agriculture. He lives in southern Indiana and works with innovative fruit, vegetable and specialty-crop farmers across the country.