Top Crop Manager

Irrigation
Water – the most important crop input in the prairie region

Standing stubble can help  maximize crop benefits from this precious resource.


November 22, 2007
By John Harapiak

The prairie region is classified as being semi-arid and that means, on average, our moisture supply is insufficient to meet crop demands. So prairie growers, especially those located in the drier soil zones, greatly appreciate the moisture provided by rainfall and snowmelt. However, I question whether or not they are doing the best they can to preserve the moisture and to maximize the efficiency with which they utilize that water.

Moisture conservation
For re-cropping in the semi-arid prairies, one of the most important factors that will help to determine the amount of crop produced is the amount of water stored in the soil and growing season precipitation. In recent years, prairie growers have made huge strides in adopting soil and moisture conserving practices. Can we do better? Research findings suggest that indeed, more can be done to make better use of our limited moisture supplies.

Soil moisture – a precious resource
In the drier portions of the Canadian prairies, the decision of whether or not to proceed with re-cropping is often dependent on the evaluation of the supply of soil-stored moisture in the spring of the year. In these regions, the odds of producing a good crop increase significantly if three or more inches of available water are stored in the soil at the time of seeding. So what can we do to improve the chances of achieving those critical extra three inches of soil-stored water?

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Minimize tillage
Brian McConkey, an AAFC researcher based at Swift Current, states that simply eliminating fall tillage can result in the conservation of an additional 0.8 to 1.6 inches of soil-stored moisture for the next crop within the Brown soils. Depending on the growing season and how efficiently the crop is using that moisture could translate into an additional three to five bushels of wheat per acre.

Capturing more moisture from snow
Capturing more of the over-the-winter snow precipitation can also be very beneficial. The amount of extra moisture that can be captured by either strip or tall stubble, as compared to cultivated stubble, can be quite worthwhile (see Table 1). In this case, in a re-cropping situation, the extra moisture captured by leaving the stubble six inches taller resulted in an additional five bushels of grain. Taller stubble can create seeding challenges. For a discussion of how southern Alberta growers manage this seeding issue, access the January and February 2006 issues of this column in the Top Crop Manager archives.

Microclimate benefits of standing stubble
Standing stubble can significantly modify the microclimate at the ground level where a young crop is being established. The influence on decreasing wind speed and evapotranspiration at the ground level is related to the height of the standing stubble. The taller stubble reduced evaporative moisture by 30 percent compared to only five percent for the shorter stubble. Obviously, increasing the height of the standing stubble pays because it enables the crop to utilize the available moisture more efficiently.

What is the role of fertilizer?
The contribution of the fertilizer you apply to the actual weight of crop harvested is really quite small. In fact, at least 95 percent of crop weight is accounted for by oxygen, carbon and hydrogen. None of these elements are derived from fertilizer, but rather from water and air. The proportion of the weight accounted for by the N, P, K and S is in the range of four percent. This is quite surprising when you consider the dramatic impact that application of
fertilizer can have on increasing crop yields. What is the explanation to this puzzle? Fertilizer boosts water use efficiency.

Since fertilizer nutrients are present in relatively small quantities in crops, one could easily assume that the role of fertilizer nutrients in crop production is minor. That idea is far from being true! Information presented in Table 2 illustrates that even surface applied N fertilizer increased both barley yield and moisture use efficiency. However, sub-surface band application of N fertilizer had an even greater impact on increasing yields and improving moisture use efficiency by the crop.

Fertilizer placement is critical
Early access to fertilizer-N as a result of band, rather than broadcast, application had a dramatic impact on the efficiency with which the barley was able to convert available water present in the soil and carbon dioxide from the air into additional yield. In the case of this trial, the soil profile was full of moisture at seeding, but the following period was drier than normal, which may have resulted in the broadcast fertilizer-N becoming temporarily stranded in the drier soil present near the soil surface. Nevertheless, the results help to clearly illustrate a very important crop production principle; crops that are properly fertilized can use soil moisture more efficiently!

Assessing spring moisture reserves
Researchers are demonstrating that the efficiency with which a crop converts available moisture into grain yield can be significantly improved based on management practices that are used. Therefore, assessing the amount of soil-stored moisture that is available in the spring can be quite important. Keep in mind that the ability of a soil to hold moisture varies with clay content. A soil that contains three inches of soil-stored moisture will be moist to a depth of 16 to 18 inches for clay soils, 20 inches for clay loams, 24 inches for loams and 36 inches for sandy loams.

John Harapiak has more than 40 years of western Canadian based fertilizer related experience. He will continue to contribute stories to Top Crop Manager. He can be contacted by e-mail: jharapiak@shaw.ca, telephone: (403) 281-3132.


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