No Till Notes: 'Predicting Yields'

Last week I wrote about the abundant moisture we have received in our area the past fall and so far this spring. I’ve also been tracking field pea and winter wheat yields over the past several years along with annual precipitation. I like to do this to see how our various dry land crops perform regarding the precipitation we receive during the growing season. Moisture is almost always the main limiting factor in crop production yields in our area.

I use moisture received from the 1st of October through the end of June the following year to measure moisture available for field peas. We plant our field peas into our dry land corn stubble from the previous corn crop and I figure our dry land corn crop is done using moisture by the end of September.

The USDA ARS research center in Akron, Colorado determined that field peas yield 3 bushels of yield per acre for each inch of moisture received. Field peas require 0.8 of an inch for vegetative growth. I have found our field pea yields are very similar to ARS findings and we have averaged 3.15 bushels/acre in yield for every inch of moisture received during the October-June time period. Our yields have ranged from 3 to 3.5 bushels/inch with last year being the high 3.5. I suspect this is due to our cooler than normal growing season last spring.

Looking ahead to this year’s field pea crop I think we have good potential to harvest an above average crop given the moisture we have received to date. So far we have received 10.41 inches of precipitation since last October.

Assuming we get our average 2.88 inches of rain in June this would give us a total of 13.29 inches for the October through June time period. This should give us a 42 bushel per acre field pea yield. I feel we will average roughly 30 bushels per acre over time with the field peas, so a 42 bushel/acre yield would be a bountiful field pea harvest.

Our winter wheat yields following the field peas have been good over the years. We plant the winter wheat directly into the field pea stubble in September following the July field pea harvest. For this moisture data I use the time period from the 1st of July when the field peas begin to dry down for harvest through the following June for the moisture the winter wheat crop gets to produce a yield. The average moisture for this time period is our yearly 15.12 inches.

Winter wheat requires 6 inches of moisture for vegetative growth and will produce roughly 6 bushels of grain yield per acre for each additional inch of precipitation. Over the past five years we have averaged 16.15 inches of precipitation each year and our average wheat yield has been 50.2 bushels per acre, excluding fields that were damaged from hail. My data would indicate that if we take 6 inches off our precipitation total of 16.15 for vegetative growth our yield would be roughly 5 bushels of grain for each additional inch received after the initial 6 inches for vegetative growth.

To date we have received 15.76 inches of precipitation since last July. The average June precipitation of 2.88 inches would give us a total of 18.64 inches.

If we take off 6 inches for vegetative growth this would leave us with 12.64 inches for grain yield. Using our 5 bushels per acre yield for each inch this would give us a total potential yield of 63.2 bushels per acre. This would be a very good wheat harvest if these yields do materialize.

I use this information in order to decide how much nitrogen fertilizer to apply to our wheat crop in the early spring. If we are in good shape for subsoil moisture like we were this spring we add additional fertilizer for the potentially higher winter wheat yields given normal rainfall through the rest of the growing season. This year we used these calculations and fertilized for a 60 bushel winter wheat crop. So far we have been receiving the moisture to achieve this yield goal. Hopefully Mother Nature will continue to provide us with the moisture we need to reach our yield goals for the growing season with our field pea and winter wheat crops.