Fertilizing forages, pastures improves growth

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The 2017 growing season is here and our forages have already started to grow. What producers do to manage growth in their hay and pasture fields the next few weeks will influence both quality and quantity of production the remainder of the growing season.

Fertilizing

I have already seen producers applying fertilizer to their hay fields and I am sure this will stimulate plant growth to increase yield and quality characteristics before harvest starts in mid-May to early June.

If hay is harvested year after year and not fertilized, soil nutrients will fall below the critical levels and production will be substantially decreased.

Soil testing every three to four years is the best way to keep track of nutrient levels.

First cutting hay usually accounts for more than one-half to two-thirds the year’s total production because the growing conditions for our cool season grasses are optimum early in the growing season.

So, if only one application of fertilizer (especially nitrogen) is going to be made per year, it is most efficiently used by forage plants during the spring. However, split applications are highly recommended for most situations.

N, P and K. Recently, while at the local farm store, I heard people ordering and pricing fertilizer they were planning to spread on their hay and pasture fields within the next few days.

What I noticed was this: They were discussing fertilizer with an analysis of 19-19-19.

While this product can certainly be used to promote growth and increase nutrients in forages, I wondered what their application rate was going to be and why they were choosing that formulation.

Forage plants do not use nutrients in that ratio, so an under-application or over-application of either phosphorus or potassium was probably going to occur, depending on the amount used per acre.

If we look at what the grass plant’s nutrient requirement is, or nutrient uptake from the soil per ton of forage, we see that plants remove about 13 pounds of phosphorus (P) and 50 pounds of potassium (K) per ton of dry matter harvested.

Therefore, if an acre yielded 2.5 ton of hay from first cutting, the removal of nutrients would be approximately 33 pounds of P and 125 pounds of K.

Nitrogen (N) is a very mobile nutrient and can readily change forms depending on soil and air conditions. That means, it can be lost due to volatilization, denitrification, leaching etc., and does not remain in the soil for long periods of time.

For most mixed grass hay stands, N will be efficiently used and cost effective if we apply 50-80 pounds of actual nitrogen per cutting.

Poor management

Let’s use 19-19-19 fertilizer for an example. If we use an application rate of 400 pounds per acre, we would be spreading 76 pounds of each nutrient N, P and K per acre.

This would provide a suitable amount of N for a first cutting predominantly grass hay and we would be in the cost-effective range of 50-80 pounds N per acre.

However, we would be over-applying phosphorus need, which was 33 pounds per acre, by 43 pounds (nearly one and a half times the needed amount) and under-applying our potassium need by 49 pounds per acre.

If a producer makes more applications of 19-19-19 for second and/or third cutting — or worse yet, multiple years in a row — one can see how the amount of nutrients in the soil can get completely out of balance.

So, the fertilizer a producer uses to fertilize hay fields should have a P to K ratio more like 1 part P to four parts K and then include the amount of N desired in the mix.

With something like a 21-11-42 analysis, the farm manager could apply various rates to match the expected yield per cutting and very closely replace the nutrients removed in the hay bales.

As farm managers, we need to understand how the wrong fertilizer applications can be financially costly and detrimental to the environment. We should use best management practices in all our efforts.

Pasture fertility

Wise use of fertilizer in the spring is an important part of pasture management, too. Most pastures require a different blend of fertilizer than hay fields.

High percentages of P and K are returned to pastures in manure so they are not removed from the field like taking hay bales off.

Soil tests will tell you what nutrients are needed. If the soil tests show P and K are adequate, nitrogen may be all you need to add.

Again, 50-80 pounds of actual N per acre, in one application, is sufficient.

Do not heavily fertilize all of your pastures early in the spring. If you need more pasture early, only fertilize a few of your paddocks. Late May or early June is a better time for pasture fertilization. This will have several benefits.

First, you are not adding to the excess growth problem most livestock managers have in the spring. Trying to keep forage plants in a vegetative state and not go to seed is hard to do.

Second, you will be providing nutrients to the forage plants at a time before warmer and dryer weather is about to begin.

The plants can use the nutrients at this time to maximize productivity before the summer slump occurs.

This provides additional growth for livestock consumption at a time when it will be needed and the quality of this forage should still be very high.

Managing growth

Managing pasture growth early in the growing season is important to maintain high quality and high quantity production in paddocks throughout the spring, summer and fall.

A spring flush naturally occurs and producers should start moving animals through the first paddocks when soil conditions permit and the plants are 4-6 inches tall.

Setting the stage for staggered regrowth is important, but often hard to accomplish. Rotate livestock through paddocks or fields at a pace which gives them just enough time to graze the tops off the forage.

Move on to the next field and let livestock graze the same way. This will allow the production of healthy plants with well-developed root systems to produce high-quality forage for future rotations.

Feed supplements

Forages in early spring pastures are extremely lush. Plant material may be only 15 percent dry matter while crude protein is generally high, possibly 25 percent.

Hay or supplemental feed should still be provided during the early rotations to be sure adequate dry matter is available in the animal’s diet.

Producers need to be sure to supply free-choice mineral mixtures with adequate amounts of magnesium (minimum of 12 percent) at this time of year too.

This reduces chances of grass tetany in livestock that are grazing grass-dominate paddocks.

Grass is growing in our part of the state. The plants, the animals and you will be rewarded for properly managing the spring flush and using fertilizer of the correct blend and amount for your fields.

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