It’s the time of year when we are all concerned about how Mother Nature is going to treat us be-cause weather drives yield. One thing we can control as growers and consultants is making sure our crop is getting the right nutrition at the right stages and the right amounts. I will use corn as an example as it is our most consistent return on fertility dollars for our area.
When thinking about fertility needs we need to first focus on the development and critical stages of our crop. In corn V5-V8 determines the girth (rows around on the ear). The next step in making yield is from V6 to just before pollination, which is right now in most of our corn fields. Our corn is determining the length of the rows of kernels on the ear. Rapid growth is happening and has been happening for the past 10 or so days. When this stage hits, water con-sumption goes up rapidly as well as nutrient uptake.
One key nutrient for this stage is nitrogen. With all of the tools we have today, we can thoroughly evaluate the need for more nitrogen. We can tissue test to look at a snap shot of what our plants are seeing, as well as whole plant testing to see what nutrients have been taken up as and the balance of nutrients in the plant.
Soil testing is an option also. My suggestion is to get a nitrate and ammonium test at the very least to determine what is in the gas tank to ensure adequate nitrogen is available when needed. I like to take tests in the side hills and low/sandy areas and then in our average producing areas of the field. If you want this done please let us know.
Is there still time to fix an issue we find through testing? The answer is YES. If you have the equipment, you can apply nitrogen or any other nutrient through Y drops that a few of you have invested in for your sprayers. Numerous ag retailers have also added this system to their arsenal of equipment also. Airplanes are another way to safely apply more nitrogen if needed. The corn crop takes up 60-65% of its Nitrogen by the time we are fully tasseled. So unless the soil is extremely short on nitrogen, you can apply nitrogen at this stage and still see a yield benefit. The best part about this timing is the fact we have a little better idea on the moisture profile and yield potential than we did at planting or traditional timing of V5-V6 side dress applications. We also know where we drowned out or burnt up due sands or gravels and saltier areas of the field. In an ideal high management system, we could vary the rates of applied nitrogen and become extremely efficient with our nitrogen dollars.
- This example is a field of mine that had nearly 6 inches of rain in a 2-day period as the corn was entering the V2 stage. As you can see there is a lot of variability within the field, and I won’t be adding nitrogen to my struggling areas of the field where my yield potential is limited.
June 20 2016
June 29 2016
July 7 2016
How to fertilize based on NDVI maps.
Dentify the different stress levels within the field.
Soil sample the zones that are identified
Identify in the field what caused the lack of growth. Shown in red on the map.
step 4 :
Customize a variable rate fertilizer recommendation and map based off of the
analysis from the lab to use in your machine or for the custom applicator
In the scenario above, my planned approach going into the season was to apply 40 lbs of actual nitrogen as a top dress application. After doing what was needed due to the recommendations that were based off of all of the above information the following is what is needed:
Low yielding zones: calls for 0 lbs of nitrogen
Medium yielding zones call for 40 lbs of nitrogen
High yielding zones calls for 30 lbs of nitrogen
This is a savings of better soil health by not putting salt on areas that won’t remove it.
This is also a savings of
14 acres x 40 lbs of Nitrogen= 560 lbs
19 acres of 10 lbs of Nitrogen = 190 lbs
750 x $0.50/lb of N = $375 / 61 acres = $6.15 an acre
We also increased our overall yield potential of this field by jumping our yield goals 15 bushels an acre on the good production, and 10 bushels on the medium production zones.
Another experiment that I wanted to learn from this field is how do cover crops effect moisture availability for the subsequent crop. Last year the whole field had oats on it, the oats were harvested for hay and then the majority of the field was drilled to a 10 way cover crop. The cover crop grew extremely well and was then grazed to approximately 30% of the original total biomass that was produced from the cover. The rest of the field was left untouched from mid-July with standing oat stubble. This spring was very wet for about a 20-day timeframe from the end of May to the first week in June. Since that time the moisture has basically shut off with the exception of a couple .10” of rain.
Non-cover crop ground started with much greater growth than the cover crop area due to soil temperature.
Dry weather proved the value of the cover crop ground by preserving moisture due to ground cover and allowing better rooting depth.
These images were taken in the same field as the example from the previous page. Image 9 was the portion of the field that was left as oat stubble. Image 10 was the portion of the field (only 3 rows away from image 9) that had cover crops on it last summer and fall.Both spots were interseeded at the exact same time, which goes to show the evidence that the cover crop preserved the moisture in Image 10, and the dry soil in Image 9 didn’t allow the shallow seeded cover crop to get established.
Corn Water Use
With the passing of this Holiday, we will be getting into our highest water use period in the South Dakota Corn Crop; and, this is also often times a stressful period for growers and corn alike. Over the next week or two for normal plant date corn we will be seeing tassel emergence and shortly thereafter we will go into silking and pollination. At these beginning reproductive stages, the water use of corn is going to be at 30-40 hundredths of an inch of water per day. After we get through the early reproductive stages and enter into blister kernel stage our water use will begin to decline until we hit Black Layer. In the chart below the long term average water use per day is shown with the black line, and the daily water use for a specific year is shown with the green line. As you can see there is quite some variability between the long term average and the specific year water use, this variability is driven by the weather conditions of a given year.
As I’m sure most everyone has seen there has been quite a bit of Leaf Rolling and Wrapping go-ing on in the fields in the last couple weeks. This Rolling of the leaves is not necessarily a sign of a total loss in yield potential, if we can catch a rain shortly after the crop begins to exhibit this symptom most of the yield loss will be negligible. This leaf rolling is a physiological response to high heat and less than ideal moisture conditions, this is the main response that corn uses when it senses moisture stress. When we will begin to see certain loss in the yield potential is when the rolled up spots begin to lose height on the plants in the rest of the field, this often most evi-dent in gravel and sand veins or areas of high salinity.
With this moisture stress we are seeing this time of year it is important to think about ways to improve the moisture holding capabilities of the soils in the future to help fend off the symptoms from these extended periods of dryness. It also seems that we are starting to see most of our rain in large quick weather events, with that being said water infiltration rates are anoth-er key factor in improving the ability of the soil to sustain the crop throughout the season. Re-ducing tillage is one the first steps towards water retention as no till and strip till allow for ground cover from last year’s stubble to remain on the surface and helps shield the ground from the beating sun before canopy. Reduced tillage also helps with the building of pore space with in the soil which is going to allow for more water holding capacity. When it comes to increasing infiltration rates, the instability of soil aggregates is often times the limiting factor. The stability of aggregates will be improved when transitioning to a reduced or no till system, but the hands down fastest way to improve aggregate stability is a small grain or grass type crop followed by a cover crop in the fall. This addition of small grain/cover crop to the rotation will also help build organic matter levels in the soil and in turn increase the water holding capacity of the soil. With all of this in mind I hope we are able to make some changes to your operation to help improve your water efficiency in the years to come.