Once the snow recedes is the time to assess small grain stands; determine whether an early topdress is required and to assess the status of some early season pests. This article will detail some points to consider that may help with management decisions.
Tillering Assessment: Spring tillering assessment is the first item to check in the field. The method can be the same as described in last month’s article for assessing plant numbers. To do this you will need a 3 foot measuring stick. Walk the field in numerous locations and drop the stick on the ground near the base of the plants and count the total number of tillers. Average the sites you check to arrive at an average tillers per three feet. The goal is to have 70–100 tillers per square foot (25–35 plants per square foot). To determine the number of tillers per square foot, calculate the average number of tillers found in the all the 3 foot measurements made, multiply by 4 and then divided by the row width in inches. This number represents tillers per square foot. For example if you checked 5 areas in a field and the average tiller count/ 3ft is 60 tillers, then you would take 60 times 4 (240) then divided by the row width(ex.7inches) to arrive at a total of 35 tillers per square foot. Since the goal is to have 70–100 tillers, this is far below the minimum. Nitrogen will be needed to stimulate more tillering and fields in this condition should be topdressed first. If you would like more detail there is a video at the CMEG Web site.
Topdress Decisions: Except to stimulate tillering, from the standpoint of crop need there is no need to top-dress N before green up. But top-dressing should be completed by the time the first node on the stem can be seen or N demand may not be met. Most wheat in our area provides straw and with the removal of straw comes the removal of phosphorus and potassium. Wheat removes 1.0 lb of P205 and 1.8 lbs of K20 per bushel of harvest. Last year, in some fields that double crop soybean crop were planted after wheat, potash deficiency showed up in the soybeans due to low levels in the soil. The point here is that unless the soil test is above optimum, compensate for P and K removal through fertilizer or manure sources.
Pest Considerations: This time of year, most pests like insects and disease are not active. However, weeds may be of concern depending on the number of weeds and there growth relative to the wheat. Weeds that encroach can hamper tillering and compete for nutrients. As you scout the wheat stands and determine the need to apply a herbicide for control, be sure to check the plants crown location. If roots are exposed from heaving or from improper planting depth, the herbicide may cause injury to the plants which will limit tillering. If this is the case then do not apply any herbicide unless absolutely necessary.
17 March 2015
15 March 2015
Interesting read with the recent resurfacing of the poly vs ortho debate. Seems like every 4 years this comes up at winter meetings.
George Rehm on 07 Mar 2010
Many farmers and ag-professionals have heard the terms “poly” and “ortho” thrown about in various marketing efforts for a variety of fertiizers. By definition, “ortho” refers to “orthophosphate” and “poly” refers to “polyphosphate”. Both are forms of phosphate in a variety of fertilizers used to supply P in crop production.
Orthophosphate is a negatively charged anion and is the form of phosphorus absorbed through the root and taken up by the plant. Polyphosphate can be thought of as a string of orthophosphate anions hooked together via chemical bonding. The size or length of the string is not fixed and can be of various lengths. Thus “polyphosphate” is simply strings of “orthophosphate” ions of various lengths. Polyphosphates are not absorbed by plant roots. In general, the phosphate in dry fertilizers exists in the “orthophosphate” form. Fluid fertilizers, on the other hand, contain phosphate in a combination of the “orthophosphate” and “polyphosphate” forms. There can always be an exception. In some fluids, all of the phosphate is present in the form of orthophosphate.
Should we expect the form of phosphate applied for corn production to affect yield? This is a frequent question from anyone who has been exposed to information originating from those who market fluid fertilizers that contain contain phosphate in the orthophosphate form. We can answer this question without considering results of any field research if the chemistry of polyphosphate in soils is considered.
When polyphosphate is added to soil, there is a chemical reaction whereby the polyphosphate is converted to orthphosphate in a short period of time. This is a purely chemical reaction and no bacteria are involved. The conversion takes 7 to 10 days to complete if soil temperatures are higher than 50 degrees F. So, if both forms of phosphate were applied to soil to supply the same rate of phosphate, equal yields should be expecteed.
Comprehensive field studies conducted in Nebraska have shown that both form of phosphate have an equal effet on yield. The calcareous soils at each of the five sites had a low soil test for phosphorus. The soils at the sites used for the study summerized in the following table had a low soil test for phosphous. The yields listed in the following table are averages for those five sites.
15 124 124
30 134 134
Average of five sites: calcareous soils
There was an increase in corn yield when each rate of phosphhate was applied. That would be expected if there was a low soil test for phosphorus. It’s also obvious that yield was not affected by the form of phosphte applied.
These results lead to the conclusion that a pounf of phosphate in a dry fertilizer (orthophosphate) is equal to a pound of phosphate in a fluid fertilizer (polyphosphate and/or orthophosphate). In the common fluids such as 10-34-0 and 7-21-7, approximately 2/3 of the phosphate is present as polyphosphate. The remainder is present as orthophosphate. So, if applied to supply the same rate of phosphate, all phosphate fertilizers . should have the same effect on yield.
The marketing information from companies that promote the use of fluids where phosphorus is in the orthophosphate form tends to add some confusion to the issue. This confusion can be attributed to a lack of understanding of “availability” and “uptake” or “utilization”
When fertilizers are in the tank or the fertilizer bin, the”availability” of the phosphate is the same regardless of the source. There are analytical procedures that can be used to measure availability and this analysis shows that availability of phosphate in dry fertilizers is equivalent to the availability of phosphate in fluids. Likewise, availability of phosphate in all fluids is equal.
The chemistry of the soil (percent calcium carbonate, organic matter percentage, etc.) determines how much will be utilized. At best, approximately 30% of applied phosphate is utilized (taken up) by corn in the year of application regardless of source. In calcareous soils, this percentage is lower.
In the fertilizer industry, the phosphate fertilizers are priced over a wide range. The fluids that have all of the phosphate in the orthophosphate form usually have the highest price tag. That high price is not justified with a superior crop response. Fertilizer prices are high. So, it’s a good idea to ask questions about the fertilizer before purchasing something new and high priced.