Calcium Products - Andrew Hoiberg, Ph.D.
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Andrew Hoiberg, Ph.D.

Andrew Hoiberg, Ph.D.

More sulfur updates...

While reading the 2012 Annual Farm Progress Reports from Iowa State University's Northern Research Farm in Kanawha, IA, we discovered another trial investigating sulfur fertilization via gypsum on corn. The impetus for the study was the same as the Iowa Soybean Association's; sulfur deficiencies are becoming widespread in both corn and alfalfa in Iowa and many other midwestern states. The experiment was performed by Dr. John Sawyer and David Rueber of Iowa State University.

Four rates of sulfur (5, 10, 20, 40 lbs/A) were applied to two different soils—one with low organic matter and a slope, and one with higher OM and less slope—as was a non-treated control (no sulfur) to compare differences throughout 2011 and 2012. These rates were applied to corn in 2011 and soybeans in 2012. The 2011 plots were planted to corn after soybean in 2011 and planted to corn again in 2012 to test residual effects of sulfur application. In 2012, additional plots were planted to soybean from corn the previous year.

In June 2011, corn leaf greenness was visibly different among plots that had sulfur applied vs. those that did not, as well as having taller plants. By late June, there was still a height difference but the color differences were diminished. Despite visual differences, there was no difference in yield between the treated and non-treated pltos.

This is where it gets interesting...

In 2012, the plots that had received sulfur in 2011 showed no visible differences from those that did not, unlike the differences in 2011. However, when harvest time came, there was an increase in corn yield for sulfur treated plots as a whole when averaged and compared against the non-treated control plots. So, there's something happening with the sulfur in the soil from year to year that isn't being accounted for that has increased corn yield as a residual effect. This is similar to what we saw with the Iowa Soybean Association On-Farm Network trials over the last few years; residual activity from sulfur application making a yield difference a year after we thought it would.

Soybeans did not show any statistically different response to the sulfur application in 2012.

This study will continue in 2013 and we are excited to see the results.


Interaction of zinc and calcium

Zinc is an extremely important micronutrient that has many roles in plant health and deficiencies are widespread, even if unknown to the grower. Recommendations for zinc levels in soils are dependent on crop, soil type, pH and other nutrient status and can range depending on which institution is offering the recommendation. Generally speaking, below 1ppm on your soil test indicates that you should apply some type of zinc fertilizer. However, growers should pay attention to their soil tests and site-specific factors, because while 1ppm of zinc in one soil type may be sufficient, 4ppm in another soil with zinc antagonists may be a better target.

Deficiency symptoms are generally seen in new growth, early in the life cycle of the plant and result in stunted growth, shortened, sometimes split internodes and discoloration of new leaves—the color of which can vary depending on plant species. Internally, zinc deficiency can result in reduced water uptake, phytohormone (hormones that regulate plant growth) activity and uptake of other nutrients. In corn, zinc deficiency results in a broad band of bleached tissue on either side of the midrib, beginning at the base of the leaf and generally staying in the lower half of the leaf. Severe zinc deficiency may result in new leaves that are nearly white, a phenomenon called 'white bud.'

Zinc availability is very sensitive to pH, and is therefore reduced by over-liming or by other agents causing high pH. However, rates and acidifying forms of N commonly used in agriculture generally alter the pH enough in the rhizosphere to enhance zinc uptake. Zinc is also well known to interact with P; where zinc is deficient, P uptake is increased in certain plants and vice versa. Zinc deficiency is also more common on cool and wet soils with low organic matter.

Specifically, we are interested in the interaction of zinc and calcium, a topic on which there exists little information. Feedback from growers indicates that when zinc levels are not sufficient, they don't see a good response from our products containing calcium. Why this happens, we are not exactly sure, however, we theorize that perhaps the limiting factor is zinc, rather than the calcium, which results in no visible effects from the application. One thing we do know is that alkaline earth cations, specifically calcium, can inhibit zinc uptake. This may have something to do with the fact that a large amount of basic cations in soil generally result in higher pH values, which is known to inhibit zinc uptake. One way to combat this problem is to apply some slightly acidifying N fertilizer that will cause a temporary shift in pH—favorable to zinc uptake—in the rhizosphere to combat the inhibitory effects from calcium. The take-home message is that if calcium-based products are needed in your system, it is prudent to pay attention to your zinc levels and adjust with a zinc fertilizer, or another method to ensure your plants are getting the requisite amount of zinc.



What does all this rain mean to your field?


Obviously, it’s been a cool, cloudy and wet spring. So much so that corn planting, as of last week, stands at only 88%, 11% behind the five-year average of 99%. Only 44% of the soybean crop has been planted, way behind the 99% we experienced last year at this time. The stark weather contrast between this year and last has not only limited farmers’ ability to get into their fields, but also may have consequences in regards to soil fertility.

During drought conditions, it is normal for a ‘bank’ of nitrogen to be stored in the soil as there isn’t sufficient moisture to move it in the soil, so it stays put. Soil samples taken by Iowa State last fall indicated that it may be possible to have upwards of 100 lbs N/A carryover to this season, which is roughly double what may normally carry over from year to year. However, with all of the moisture that has fallen this spring, a significant amount of that nitrogen may have already leached out of the soil.

My suspicion is that the same thing may be happening with sulfate as well. Observations that I’ve made as I drove past corn fields last week generally show a yellowish, chlorotic plant that is starved for nutrition, at the V3-V6 stages on average.

The Iowa Soybean association is recommending farmers do a late-spring, pre-sidedress soil nitrate analysis in early June when the plants are 6-12 inches tall. The benefit of this test is that it predicts the amount of nitrogen available before the corn plant begins taking up more nutrients as it matures. ISA is recommending that if the test shows less than 21ppm nitrate, there is a high probability that the cost of an additional nitrogen application would be covered by the increase in yield you will see from that application. It’s completely up to the individual, but it may also be worthwhile to consider a sulfate source to sidedress along with additional nitrogen.

There are other compounding factors when soil is waterlogged for prolonged periods. Not only does the saturated soil predispose corn and other plants to disease pressure, it depletes the soil of oxygen, which has many negative impacts on plants. One of which tends to be exacerbated when it happens early in the season is restriction of root growth and development. Fortunately, we are not dealing with temperature extremes along with the saturated soil which would make the situation even worse. Things look to warm up this week; hopefully the soil will start to dry out a bit so we can all get back to our regularly scheduled growing season!




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