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When to fertilize your forage crop

woman standing in a canola field

Fertilizing forages pays off in the long run and could be a game changer if the race gets called on account of weather. Like any crop, forages need a significant amount of nutrients during the growing season to replace the nutrients removed with the crop, says Charlotte Ward, a forage specialist with the Saskatchewan Ministry of Agriculture (SMA).

As a rule of thumb, if less than half the forage taken is legumes, fertilize the aftermath as a grass, focusing on nitrogen. If more than half is legumes, fertilize for a legume focusing on phosphorus, potassium and sulphur. Numerous studies show there’s no benefit in applying nitrogen to heavy legume stands because it only displaces the nitrogen the alfalfa would have fixed on its own.

“Oftentimes we get caught up in the agronomy, but we don’t bring it back to how it pencils out on the farm,” Ward says.

The economics of fertilizing hayfields boil down to the cost relative to the value of the expected increase in yield and the cost of baling and hauling the additional tonnage. It also pays to look at the cost of some other ways to get extra forage such as renting pasture or buying standing forage, baled hay, straw or supplements, sod seed legumes into an established stand, or ripping up cropland and planting more forages.

In a webinar on forage fertilizer economics last month Ward made use of the SMA’s new Economics of Commercial Fertilizer for Hay and Pasture Calculator.

If you want to use it you’ll need to gather some numbers to start. First, enter the type of fertilizer you plan to apply, the rate and cost per tonne with application costs, plus your expected dry-matter (DM) response.

One pound of actual N per acre is expected to boost forage DM yield by 20 to 35 pounds per acre (lbs./ac.). Ward expects to gain 25 lbs./ac. more forage, pretty typical under good weather on the black soil of east-central Saskatchewan. Keep your expectations realistic, she advises, because many variables will affect the actual result… the level of nutrients already in the soil, past management practices, organic content of the soil, the species in your mix, the list is endless.

You will need the moisture content at harvest, plus your value of the standing hay (in dollars per ton as if it’s baled) to calculate a return on investment. The program ignores the cost of baling and hauling so Ward adds them at the end using prices from the provincial custom rate guide.

The calculator churns out the value of the standing hay, the additional yield both as-fed and dry matter, the total fertilizer and application cost/acre, and the net profit or loss/acre associated with the fertilizer application.

The pasture worksheet requires input on cow weight, consumption as a percentage of body weight, unused production, and grazing fees. It calculates DM consumption in pounds/day, DM production from fertilizing, additional cow days/acre, added value of pasture production from fertilizing and fertilizer cost/acre, to roll out the net return or loss.

You’ll also need to add your land and establishment cost for accurate comparisons of various scenarios. SMA’s Hay Share Calculator can be used for that and to figure out the value of standing hay and hay rent shares. The land and establishment cost for the following scenarios came to $42/acre/year.

What if you lose hay land?

Thirty per cent of the stand (450 acres) is under water, leaving 1,050 harvestable acres from which to get the usual number of bales. Production will have to be bumped up to 1.78 tons/acre. That’s an extra 0.53 tons, 1,071 lbs./ac. as-fed, or 930 lbs. DM/acre when baled at 13 per cent moisture.

If one pound of N boosts forage DM yield by 25 lbs./ac., then 37 lbs. N/acre should suffice to meet the 930-lb. DM target. The calculator pegs fertilizer and application costs at $23,450 for the 1,050 acres. With haying and hauling costs added on, the overall cost per bale is $32.62.

Alternatively, the producer could choose to fertilize fewer acres at a higher rate to get the same production. If half the hayfield had been fertilized with 50 lbs. N/acre, the cost per bale would have been $35.73. Land and establishment cost isn’t included in the comparison of the two application scenarios.

Does it pay to kick-start an old hayfield?

Fertilizing with 50 lbs. N/acre would increase forage DM yield by 1,250 lbs./ac., or 1,438 lbs./ac. as-fed. That works out to 2.63 bales/acre, or almost one additional bale an acre compared to the starting point of 1.66 bales/acre. Fertilizing 260 acres would meet the increased hay requirement. The additional 250 bales worked out to $12,000, or $48/bale.

The bill for buying an additional 187 tons of hay at the local price of $80/ton is $15,000, or $60/bale and there would be transportation costs on top of that.

The third option is to establish a new legume-grass stand with a higher percentage of legume in the mix. The expected yield is 2.0 tons/acre, or 2.67 bales/acre, therefore, 94 acres of additional land would be needed to produce the extra 250 bales. The total cost for this scenario is $101/acre, or $38/bale.

“This looks like the cheapest way to increase production but it tied up 94 acres, which might not fit into your farm plan,” cautions Ward. The disadvantage is the lag in production unless a companion crop is grown to produce greenfeed the first year. The advantages are that it gives time to rejuvenate the old stand and it will be three years before the new stand will need to be fertilized with the goal of maintaining the high percentage of alfalfa and yield.

Staying in front of the 8-ball

Instead of getting 1.25 tons/acre in each of the next three years for a total 3.75 tons/acre or five bales per acre, she expects to maintain 2.0 tons/acre/year for a total of 6.0 tons/acre or eight bales/acre. That’s an increase of 2.25 tons/acre (6.0-3.75), or 4,500 lbs. as-fed with 3,915 lbs. DM.

The all-in cost without fertilizing is $252/acre or $50.48/bale over the three years. Fertilizing increases the overall cost to $353/acre, but the cost per bale is lower because it’s spread over the higher yield, coming in at $44.14/bale for three years.

“You are actually saving $6.34 per bale across the three years by fertilizing. Maybe that doesn’t seem like much, but you’ve maintained production and prolonged the life of the stand,” says Ward. Fertilizing to improve yield could produce extra hay to sell, support more animals or reduce the land requirement for hay production. Fewer acres to cover during haying season reduces time and labour cost and could improve chances of getting the hay put up in good condition.

Her take-away message is to plan fertility rather than using it to fix a problem after the fact. “Soil fertility is an investment in your stand because it will keep plants healthy with improved vigour for early-spring growth and tolerance to (environmental) and grazing stresses.

“Commercial fertilizer isn’t a substitute for good management, though. In lots of cases fertilizing doesn’t pencil out,” she says.

Webinars on many forage and beef production topics are available free of charge at the Saskatchewan Ministry of Agriculture website.

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