Crop Rotations - A Small Management Decision With A BIG Impact

Think of a single management decision that could set the stage for your crop’s yield potential right out of the gate. Now think about that same decision potentially setting-up your cropping limitations for the next 3 to 4 years. It is the much preached, but seldom considered crop rotation plan.

Farmers are very vocal that they need to plant according to what will pay the bills, but this could be short-sighted as that enticing price in January – March is not what is locked in for November delivery! To show the value of crop rotation, lets look at the impact a diverse rotation and a tight rotation has on crop performance and cash flow.

Scenario 1: What Was Planted This Year Impacts Your Yield Potential Next Year.

Table 1: Yield Response of Major Manitoba Crops Sown on Various Previous Crops (stubble) in Rotation (source: MASC 1998-2007 Harvest Production Reports)

Table 1, using crop performance on wheat stubble as a baseline, demonstrates that planting the same crop two years in a row can reduce yields by 15%. It also shows that growing certain crop combinations on stubble, such as flax on canola, really do not work. Negative interactions that result from planting a crop on another crop’s stubble can be due to things like disease or soil residual herbicide carryover.

Scenario 2: Tight Crop Rotations And Increased Disease.

Small plot research trials have demonstrated a link between tight canola rotations and the increase in blackleg. As blackleg pressure and incidence increases, resistance to blackleg fails and yields go down. Dr. Debbie McLaren from AAFC Brandon conducted an interesting real-life study looking at how often canola was grown in the rotation and the corresponding disease levels in the same fields. Dr. McLaren and her team identified fields with different rotation frequencies (canola back to back, 1 in 2 years, 1 in 3 years, 1 in 4 years, 1 in 5 years) and surveyed them for disease presence. What they found validated small plot research trial results – the tighter the canola rotation (or more intense canola frequency in rotation) the higher the amount of diseased plants in the field (Figure 1).

Figure 1: Impact of Frequency of Canola in Rotation and Prevalence of Sclerotinia and Blackleg in Crop (Source: D.L. McLaren, AAFC Brandon. Unpublished)

Tight canola rotation/blackleg is not the only concern when planning a crop rotation to reduce disease. Other crops/diseases can show a link between tight crop rotation and disease incidence. These include Fusarium Head Blight in wheat, barley and oat; Goss's Wilt in corn; Pasmo in flax; and Ascochyta in field peas. Lengthening the time between any one crop in rotation can help with controlling disease now and in the future.

Scenario 3: Impact On Net Returns

Right now, regardless of what you are planning to grow, commodity prices are making everything look good. Is this the year to put in a different crop and maybe break up a tight rotation? What about in years when commodity prices are not so good – will diverse crop rotation pay over a longer period of time? Or does it pay to keep the high profiting canola in a canola-cereal-canola-cereal rotation?

The revenue of the crop rotation in this scenario (Table 2) looks at net profits (gross profits minus operating costs).

Table 2: Net Profit of Manitoba Crops with and without Fungicide Applications.

In Table 3 there are three potential crop rotations varying the length between canola crops and the net profit of each crop per year. Looking at a six year rotation, things look promising in all three rotations, but as successive canola is planted in the tight rotation (Rotation Plan #1), disease may start to be evident (see Figure 1) and yields may go down or you may need additional fungicide help. In Year 3 on the tight canola rotation (#1), a fungicide is added, as well as in year 5, in hopes that the yield will still remain. The addition of the fungicide reduces net returns by $20/year where tight canola or wheat in rotation are shown. In the other two scenarios no additional fungicide costs were added.

Table 3: Net Returns of Crops in Rotation over a Six Year Period.

From the rotation/economics scenarios it demonstrates that even when lower net return crops are planted, money can still be made. The addition of a fungicide to maintain yields or the reduction in yield due to disease build-up can take away whatever added bonus the commodity market will give you for growing the same top grossing crop year after year after year.

In conclusion, agronomically sound crop rotations can work for the health of your crop and make you money! It does not take extra machinery or extra inputs to make it work, just a plan. Even in years where commodity prices are not so favorable an agronomically sound crop rotation can add value to your bottom line as you may not have the extra fungicide costs needed to maintain yields. In addition, in some years other crops may end up having a high price in fall that was not expected in the spring. With a more diverse crop rotation you could take advantage of this by spreading out the markets that you are targeting to deliver into.

For further information or to find out more about shared disease between crops, herbicide carry-over risks, or other interactions that could affect your yields, talk to one of our crops staff. MB ARD office