Ways to combat yield loss in the second year

Thursday, January 2, 2014

If you grow the same crop for a second year, you can expect a yield drop. But there are things you can do to combat this, among them – using more nitrogen

by PAT LYNCH

One of the basics of crop production is crop rotation. Usually, the more crops in rotation, the higher the yield of each crop.

If you grow the same crop for a second year, you can expect a yield drop. Typically there is a 10 per cent yield reduction when corn is planted after corn or soybeans after soybeans or wheat after wheat. If you are on a heavy soil, there can be a 50 per cent yield reduction if corn or wheat is planted after the same crop.

There are exceptions to this rule. When you grow soybeans the second time ever on the same soil, typically the yield is higher than the first time you grew them. If you have deep silt loam soil, the yield decrease for the same crop the second year can be less than 10 per cent. In fact some of the world's highest corn yields have been grown on fields that were in continuous corn. These are exceptions. And there is a year effect. Growers have told me that the second year they grew corn on a certain farm, the yield was higher than the first year. But weather, hybrid and other management things had changed.

But the reality for next year is that some farms will be planted to the same crop as they were in 2013. This may be because of no wheat planted or just the mix of crops on other fields. Or it may be related to commodity prices, or the need for on-farm feed.

There are things you can do to increase yield on second-year crops. First, if you have to plant some acres a second year to the same crop, plant them first on lighter silt and loam soils.

Change the variety/hybrid that you planted in 2013. No matter how much a hybrid or variety yielded on a certain farm in 2013, the diseases that started on the roots in 2013 will be at a high level in 2014.

The biggest cause of yield reduction in second-year crops is the diseases, insects and nematodes in the soil. Typically, different hybrids/varieties will have different genetic resistance to the disease in your farm. In the case of the soybean cyst nematode (SCN), try and use a variety with different genetic resistance to it.

Also, be aware that you will have more diseases, both above ground and below ground. Having a good seedbed is paramount to getting quick emergence of your second-year crop. Use seed treatments. If you are planting corn on corn, use a hybrid with resistance to corn rootworm. Consider using foliar fungicides on both corn and soybeans. If you had anthracnose in your area in 2013, you may need to spray twice for anthracnose in 2014. If you had bad white mould in 2013, the probability of having a yield loss to mould in 2014 is high. For those fields, plant corn.

You will need more nitrogen when planting corn after corn. Use the nitrogen calculator. Typically, it will recommend 20-30 pounds more nitrogen per acre for second-year corn.

I like nitrogen on soybeans when you plant a second time. The Ontario agriculture ministry's soybean specialist will disagree with this recommendation. But if you are on heavy soil and especially if you are in an area with SCN, consider 30 pounds per acre of nitrogen.

Weeds typically are worse in the second year than the first. You should use a pre-emerge soil residual herbicide in all Roundup Ready second-year crops. Just know that any weed that escaped in 2013 will be much worse in 2014.

And scout second-year fields more diligently than first-year fields. They generally have more problems. BF

Consulting agronomist Pat Lynch, CCA (ON), formerly worked with the Ontario agriculture ministry and with Cargill.