Planning fertilizer for forage crops

Some food for thought on fertilization to establish forage crops in your fields

Kevin Elmy of Saltcoats, Sask., uses a wide variety of plant species in his cover crop mix.

Forage crops are sometimes treated as the neglected child. Once it is established, come along with a haybine if there is enough rain to make a crop. If it continues to rain after the bales are off maybe even come in to get a small second cut. Grass hay crops are often left to wither away to low yields and broken up as “sod bound.” What follows is more food for thought than any specific recipes.

Grass hay

Nitrogen: Most “sod bound” grass fields just need a good dose of N fertilizer to kick them into gear. Nitrogen is the big deficiency in almost all grass stands. If the stand is not weedy, a shot of 100 pounds of N/acre will kick it into gear — as long as there is moisture in the soil or rain comes along early.

An average of 28 site years of data from west central and northwest Saskatchewan from years ago showed a doubling to tripling of hay yield from a single broadcast application of 100 lbs. N/ac.

Many sites also showed substantial residual effects into the second and even third year after such an application.

In the good old days we still had ammonium nitrate fertilizer (34-0-0) with little volatile loss when surface broadcast. We now have mostly urea, which is subject to loss, but much forage fertilizer data shows less loss than we might fear. And, in today’s world there are enhanced urea fertilizer options that are less subject to volatile loss.

Phosphorus: Nitrogen is so limiting for grass crops that response to low rates of broadcast P fertilizer are small, if any. But, when yields are pushed with N, then P will be required and the responses will be cumulative for multi-year applications.

The need for P really kicks in when yields are pushed with large and repeated N fertilizer.

Potassium: Most Prairie soils still have lots of K but where soil test is marginal K will be needed.

Sulphur: S is a big issue for Grey Wooded soils and full N response will not be obtained without it.

Alfalfa hay

Nitrogen: Alfalfa is still the queen of hay crops — especially for dairy cows. Being a high nitrogen-fixing legume takes care of the N requirements, but other nutrients are required.

Phosphorus: Alfalfa yield response to P is not as dramatic as the N response on grass, but P will be needed in the long term. Each tonne of hay removes about 15 pounds of P2O5 per acre.

Potassium: Each tonne of hay will haul away about 60 lbs. K2O/acre, so marginally K deficient soils will soon need K.

Sulphur: Alfalfa has a high S requirement and will be needed for marginally deficient soils. On grey wooded soils early alfalfa crops failed until S fertilizers were used.

Alfalfa/grass mixtures make for good quality hay but maintenance of the ideal mixture can be a problem. Any high N fertilizer rate will favor the grass and squeeze out the legume.

The morning after: The negatives

There is often the concept that when a forage crop is broken up the land will be like new breaking and little fertilizer will be required. If it was a good crop of pure alfalfa then, usually, the N requirements of the next annual crop will be met.

Moisture: Perennial forage crops use water from snow melt to freeze up and the soil profile will be depleted to considerable depth. Soil probing should confirm adequate moisture before committing expensive inputs to an annual crop.

Moisture is the main reason forage crops, in regular rotation with annual crops, have never been popular in the brown and dark brown soil zones. It simply did not work because of moisture deficiency!

Our recent seven years of natural irrigation in parts of the Canadian Prairies has changed all that for now. I took my trusty soil probe late last fall to a grass pasture right next my barley crop and found no dry soil. But, this cycle will end and we will again need to consider moisture as No. 1.

Phosphorus: Apart from N after alfalfa there are few residual effects after forage. In fact, hay crops remove the entire plant so several years of good hay yields can lead to severe P deficiencies. Deficiencies of K and S can also kick in where the soil test is marginal.

The morning after: The positives

For most of our annual crops, the recent wet cycle has juiced up inoculum of plant diseases of most of out annual crops. Sclerotina of canola, fusarium head blight of wheat and various root pathogens of pulse crops are major headaches. Especially for FHB, fungicides are a Band-Aid and genetic resistance is partial at best.

That leaves rotation as the best option. That rotation could include forage crops — if it can be made practical and economic. Potato growers have faced this problem for years — potatoes can only be grown every fourth year. So, what is a potato grower to do to keep the land out of mischief for three of four years?

At the irrigation area at Outlook, Sask., the answer has been renting land from regular crop farmers and moving around to make it all work.

Is there any such thing as an alliance between stubble jumpers and cowboys? In most areas the limitation would be too few cowboys but maybe it would work in some areas. But the few years of relief from annual crop disease could be a big issue.

Modern cowboys and pasture management

I watch with interest the soil health discussions around pasture management. Innovators are using many plant species including legumes, and mob grazing of small areas for a limited time.

It was my great pleasure to attend the recent annual meeting of our Saskatchewan Soil Conservation Association this year. The topic was soil health and included several excellent presentations by farmers who are actually making it work.

Those practices achieve much biodiversity and recycling of manure nutrients with a reasonable distribution and with no diesel fuel to haul. It seems that the farmers are ahead of the research on this one. Not the first time — they did that with zero till as well.

Well known Gabe Brown of Minot, ND, made the point that annual crops only capture CO2 for about 70 days per year and cover crops extend that greatly. When it comes to moisture use, the effect is even greater. Our annual crops, planted mid May only really suck significant water out of the soil from about mid June to late July. In our current wet cycle annual crops are just not cutting it to suck up enough water.

In the fall of 2016 my barley came off in late August and a good catch of volunteer canola, some barley and some sow thistle type weeds took off. In dry cycles that growth would be dealt with to save moisture. But this year it was “grow, grow, grow! Use up all the water you want — we have too much already.”

But, in dry areas and when dry returns to our area , the cover crop idea will fail due to lack of water.

So, there you have it — more food for though than any specific silver bullets.

More information

If CCA and P.Ag types want to delve into the topic in more detail, this paper will provide a good start: “Fertilizer Management of Forage Crops in the Canadian Great Plains,” by S.S. Malhi and D.H. McCartney. At the time of writing (2004), the authors were with AAFC.

About the author


Les Henry

J.L.(Les) Henry is a former professor and extension specialist at the University of Saskatchewan. He farms at Dundurn, Sask. He recently finished a second printing of “Henry’s Handbook of Soil and Water,” a book that mixes the basics and practical aspects of soil, fertilizer and farming. Les will cover the shipping and GST for “Grainews” readers. Simply send a cheque for $50 to Henry Perspectives, 143 Tucker Cres., Saskatoon, Sask., S7H 3H7, and he will dispatch a signed book.



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