THE LAND, SEPTEMBER 27, 2013
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Rains, but also wind, come for Iowa Iowa received some much needed precipitation during the week ending Sept. 22, according to the U.S. Department of Agriculture National Agricultural Statistics Service.
short, 41 percent short, 23 percent adequate and zero percent surplus. Subsoil moisture levels rated 41 percent very short, 40 percent short, 19 percent adequate and zero percent surplus.
Areas of central Iowa experienced wind damage from Thursday evening’s storm. Statewide there were 5.6 days suitable for fieldwork. Other activities for the week included chopping corn silage and harvesting seed corn.
Southeast Iowa was the driest with 97 percent of topsoil moisture rated in the very short and short categories.
Topsoil moisture levels rated 36 percent very
With almost the entire corn crop in or past the dough stage, 89 percent of the crop was dented, 6 percentage points behind normal. Thirty-five per-
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Formula helps when estimating soybean crop yield potential Soybean producers can easily get an idea of the yield potential of their crops with a Purdue Extension soybean specialist’s calculation method. Soybean yield potential is built on many factors, including the genetics selected, management decisions during the season and the weather. Yield components of soybeans are pods, seed size and number of seeds per pod. “Individual plant production varies, and every field will vary based on pests, soils, fertility and other factors,” said Shaun Casteel. “But I’ve simplified the process of estimating soybean yields so that producers can scout multiple areas quickly while maintaining representative estimates.” Casteel’s system is based on estimated yield in one ten-thousandth of an acre. The basic formula involves multiplying the number of pods by the number of seeds per pod, then dividing that result by the seed size factor. That calculation will show the estimated bushels per acre. To calculate, producers first need to count the number of pods in one ten-thousandth of an acre, an area determined by a 21-inch length of a row of plants and how far apart the rows were planted. “Nearly 90 percent of our Indiana soybean acres are planted in 30-, 15- or 7.5-inch rows, so just remember that each count needs to be 21 inches long,” Casteel said. “You will count the number of pods in one row for 30inch width, two rows for 15-inch and four rows for 7.5-inch.” Producers should count the number of pods that are at stage R5 or higher — when they can see seeds. Next, they must determine the number of seeds per pod. Casteel said using the average of 2.5 seeds per pod is best because there can be a range of one to four seeds per pod. “This value is conser-
vative since we don’t know exactly how the rest of the season will finish,” Casteel said. Changing this one value can increase or decrease yield estimates. The third step is to calculate seed size factor. Casteel said the starting point is seed size factor 18, equaling about 3,000 seeds per pound. “If you expect larger seeds from late-season rains, you would divide by a lower seed size factor such as 15, which equals about 2,500 seeds per pound,” he said. “If the field has late-season stress, such as a lack of water, you would divide by a higher seed size factor like 21, or 3,500 seeds per pound.” The three values — number of pods in stage R5 or higher, number of seeds per pod and seed size factor — go into Casteel’s equation. For example, 250 pods times 2.5 seeds per pod divided by a seed size factor 15 equals 41.7 bushels per acre. Fair soybean growth with limited pod retention but with good late-season moisture will result in a fair crop. Although producers can start estimating yields as soybeans enter the R5 stage, the estimates will be more accurate as soybeans develop and enter R6, or full seed. If soybeans are just coming into R6, Casteel said the yield potential still depends on pod retention and seed size. The weather is an important contributor to yield potential, and dry conditions over the past four to five weeks have lowered yield potential in some fields. “Reductions in excessive heat and the return of rain helped yield potentials more in seed size than pod retention assuming the soybeans are into R6 and beginning to drop leaves,” Casteel said. “If fields are green, soybean yield potentials could improve. If fields are losing foliage, yield gains will be very limited.” This article was submitted by the Purdue University Agricultural Communications Department. ❖
cent of corn was mature, well behind the normal 61 percent. Some farmers reported harvesting their earliest planted corn. Corn condition improved slightly to 9 percent very poor, 18 percent poor, 36 percent fair, 32 percent good and 5 percent excellent. Sixty-nine percent of soybeans had turned color, 20 percentage points behind normal. Twenty-two percent of the crop had dropped leaves, 10 days behind normal pace. There were scattered reports of the earliest planted soybeans being harvested. Soybean condition also improved slightly to 10 percent very poor, 19 percent poor, 37 percent fair, 30 percent good and 4 percent excellent. The harvest of third-cutting alfalfa was 96 percent complete, slightly ahead of the normal 93 percent. Pasture condition improved and was rated 32 percent very poor, 30 percent poor, 27 percent fair, 10 percent good and 1 percent excellent. The condition of Minnesota’s crops improved during the week ending Sept. 22. Statewide, an average of 0.43 inch of rain fell; improving topsoil and subsoil moisture to 51 and 43 percent adequate, respectively. Central Minnesota received 0.96 inch of rainfall making it the wettest region for the second consecutive week. Temperatures averaged 57.2 degrees, 0.3 degrees cooler than normal. Statewide, 5.2 days were rated suitable for fieldwork. Ninety-one percent of the corn crop was at or beyond the dent stage, remaining behind the normal 94 percent. Seventeen percent of Minnesota’s corn was mature, 12 days behind normal. Seventy-six percent of corn silage has been cut, two percentage points ahead of normal, yet behind last year’s 99 percent. Corn conditions were rated 4 percent very poor, 9 percent poor, 37 percent fair, 45 percent good and 5 percent excellent. Seventy-nine percent of the soybean crop was turning yellow, 20 percentage points behind last year. Forty-six percent of soybeans were dropping leaves, six days behind normal. Soybean conditions improved slightly to 50 percent good or excellent. Dry beans were 28 percent harvested, compared to last year’s 85 percent. The sugar beet harvest has begun, with 5 percent of the crop lifted. Minnesota’s potatoes were 58 percent dug, while sweet corn was 89 percent harvested. Pasture conditions also improved and were rated 27 percent good to excellent, compared to 17 percent a year ago. The harvest of third-cutting alfalfa was 93 percent complete. ❖