You may not get a great return from every crop in a rotation, but that doesn't mean you should quit growing those that don't pay as well as others. 

That's the advice of Dwayne Beck of Dakota Lakes Research Farm at Pierre, South Dakota, North America's foremost researcher in rotations.

"On dryland, peas give me some of my lowest returns," he says. "But, they more than compensate for that by increasing my returns from wheat following the peas. Margins from the whole rotation count for more than returns from individual crops." 

 Cover crops may provide no cash return and there's a cost to growing them, but Beck believes they have real value, even in very dry regions. 

"You may need a fallow period somewhere in your rotation," he says. "Not a 16 month fallow, something shorter, say between silage harvest and spring seeding. If you put in a cover crop for that time, you gain organic matter rather than losing it and you can gain soil moisture." Bob Blackshaw of the Lethbridge Research Centre confirms this. He's found more spring soil moisture after a cover crop than after fallow, even where chinooks vaporize most of the snow. 

Beck also uses cover crops to "fake out" disease organisms. Many fungal diseases overwinter on crop residue as spores that can stay dormant for months or even years. Once there's a canopy, though, the spores germinate, but before they can complete their life cycle and cause a disease, you terminate the cover crop. The inoculum of disease is reduced more than by fallow. The weed seed bank and perennial weeds can be reduced by cover crops too. Weeds emerge with the crop and then they're terminated before they can set seed or replenish the nutrient reserves used in early growth. 

Beck is opposed to a full year of fallow because the normal precipitation is greater than the water holding capacity of the soil. "Soils hold up to 2 inches of available water per foot," he says. "So, at most, the top four feet of soil can hold 8 inches of water. Average precipitation at Medicine Hat is 12 inches. The other 4 inches is going to run off, waterlog the soil or leach out of the bottom of the soil profile and cause problems. 

"We have to gear our rotations to the long term, quit wasting water with tillage and disturbance and use a mulch layer to cut down evaporation. If crops didn't fail in a year as dry as 2001, your rotation isn't intense enough. You're wasting water.  

"Some of the worst problems in dry areas are caused by too much water. In parts of Australia, farmers have taken out the trees to grow shallow rooted crops that can't reach deep stores of water the trees used. Salinity has become a huge problem." In a region like southern Alberta, where it's normal to have abnormal weather patterns, a good rotation, one with diverse crops, can be a form of insurance. Weather that's hard on one type of crop may be good for another.