With corn harvest nearing there may be some questions about harvesting corn stover for feeding beef cattle. There are some implications for the crop farmer with regard to nutrient removal, future nitrogen needs, organic matter and erosion control.
Grain yield is usually about 45-50% of the total dry matter yield of a corn field. It is estimated that a 140 bu/ac corn field leaves about 4 ton/ac of roughage (at 25-30% moisture). Table 1 includes some nutrient content values from past Manitoba studies1 compared to those of the International Plant Nutrition Institute2.
Table 1. Crop nutrient removal with a 140-150 bu/ac corn crop.
|Stover amount||Nitrogen (N)||Phosphorus (P2O5)||Potassium (K2O)||Sulphur
|IPNI average||Per dry ton||19||5.7||32||–|
|MB Ag||Per dry ton||12||4||34||1|
|Lb nutrient /acre|
|All stover removed||At 4 t/ac
(2.7 DM ton)
|½ stover removed||At 2 t/ac||17||5||48||2|
What is the approximate value of fertilizer nutrients removed in stover?
Using the MB Ag values from table 1, the approximate value of nitrogen, phosphorus, potassium and sulphur per dry ton of harvested corn stover is $6, $2.40, $10.20 and $0.40, respectively (based on fertilizer prices of $0.50/lb N, $0.60/lb P2O5, $0.30/lb K2O and $0.40 /lb S) for a total nutrient value of $19/ton. If harvested stover yields are 4 ton/ac (2.7 dry ton/ac), the total value of nutrients removed from the field would be $51.30/acre. Since the full stover amount is seldom harvested, the removal would be reduced accordingly. Note that over half the nutrient value removed is as potassium.
One might conclude that all nutrients need to be replaced to sustain continued crop production. But this may not be the case:
- clay textured soils in Manitoba tend to have high natural reserves of potassium.
- Potassium is readily leached from mature crop residues, so rained on and delayed corn stover removal will leave much of the potassium in the field.
- since stover harvest is done only occasionally, it will impact soil test levels slightly
- nitrogen requirements may actually be less for the next crop (read on)
Nitrogen needs of the following crop may actually be reduced when some corn residue is removed. With the typically high residue loads of corn stover and the relatively high C:N ratio, inorganic soil N levels can be depressed during residue decomposition, called immobilization. This temporary tie up of nitrogen by microbes to breakdown residue will be less if there is less stover. US studies with corn following corn have shown that optimum N rates may be 10-45 lb less N per acre when half the residue is removed. We grow little corn following corn here so may not such large differences.
Now if corn stover was grazed by cattle, many of these fertilizer nutrients would simply remain in the field, but most crop farmers want cattle off the field so they can complete fall tillage operations to prepare for the 2019 crop season.
Erosion, organic matter levels and soil structure would be negatively affected by full and continuous removal of corn stover, but not likely by occasional removal. Mechanical harvesting (usually stover cutting with a rotary hay cutter, raking with a double rake, then baling) may only remove some 40% of the total stover biomass, generally leaving sufficient soil cover. And since Manitoba corn stover is usually aggressively tilled, this reduced cover will require less than normal tillage to prepare a seedbed for springtime.
In summary, the occasional removal of a portion of the corn stover should have minimal effect on soil properties – other than nutrients. Soil testing is important to know if you have such nutrients to spare or how much to charge for such removal.
1 Heard, J. 2004. http://www.umanitoba.ca/faculties/afs/MAC_proceedings/proceedings/2004/heard_nutrient_uptake_corn.pdf
2Fixen, P. 2007. Better Crops/Vol 91, no.1) https://www.ipni.net/ppiweb/bcrops.nsf/$webindex/BD81AB2128ECC7D2852572DE005B4364/$file/07-2p12.pdf