You can’t change the weather. But knowledge and technology can help crops cope with any curveballs Mother Nature throws your way. “Weatherproofing fertility reduces seasonal stress, resulting in higher yields and a better return on the money you spend on inputs,” says Farm Journal Field Agronomist Ken Ferrie. “Over time, it produces more consistent yields, which impresses landlords. In addition, reducing nutrient losses protects water supplies and identifies you as a good steward of natural resources.” When you think about it, Ferrie adds, weatherproofing fertility is simply applying the 4Rs—right product, right rate, right time and right place.
Timing and placement, in particular, help counter weather threats. Runoff is a concern on frozen ground and on ground that receives rainfall exceeding the soil’s infiltration rate. On sloping fields, nutrients can be carried away on eroded soil particles. Nitrogen and sulfur can be released as gas (from volatilization and denitrification) into the atmosphere in areas where poor drainage causes ponding and saturated soils. Ferrie shares the following tips for nutrient timing and placement in various weather challenges: 1. On some soils, runoff, erosion and poor drainage issues arise every year. Applying nutrients as closely as possible to crop usage counters the threat. So does injecting or promptly incorporating fertilizer. “On those fields, don’t leave nutrients on the surface any longer than necessary,” Ferrie says. 2. When rain is plentiful, there’s a bigger chance for nutrient loss. “On soils prone to leaching, switch nitrogen and sulfur applications from fall to spring,” Ferrie advises. “When you apply sulfur in the spring, use the sulfate form. Elemental sulfur might not have time to convert to sulfate, the form plants need early in the season.” In the spring, apply nitrogen and sulfur in the row-warming pass prior to planting or with the planter. “Banding fertilizer also protects it from becoming as tied up in the soil and unavailable to plants,” Ferrie explains. “In cold weather, it keeps roots growing until they’re able to find nutrients on their own. In our plots, any nutrient applied in a band is usually twice as effective in the plant.” Other options for applying fertilizer closer to the time of use include side-dressing with a traditional colter toolbar or placing nitrogen close to the row in the stem-water area (where dew or light rain moves down the stalk). NutraBoss, Unverferth Manufacturing and 360 Yield Center offer tools that place fertilizer in the stem-water area. “We can also broadcast nitrogen and sulfur in the spring,” Ferrie says, “but that’s the least effective method. If you broadcast nitrogen in the spring, and heavy rainfall delays planting, the nitrogen might leach below the roots, causing plant growth to stall or slow down.” Even with timely applications, it’s still important to monitor nutrients through the growing season, Ferrie adds. “With highly leachable soil, you might need to make a rescue application of nitrogen, or add it to the irrigation water, to make up for losses.” 3.Dry weather brings worries about nutrient availability, rather than nutrient loss. “In dry conditions, many nutrients come up short, especially those that depend on mass flow to enter plant roots,” Ferrie says. “And soil biology slows down, so microorganisms no longer mineralize, or release, nutrients.” The first step to weatherproofing against drought is maintaining balanced fertility levels. “When fertility is in good shape, the soil is more capable of handling adversity,” Ferrie says. “This is especially true with pH—acid soils can’t handle drought.” Eliminating soil compaction helps minimize the impact of dry conditions, by facilitating root penetration and water movement through the soil. So does placing nutrients in the stem-water area. If you apply nitrogen with a colter in heavy clay soil, you risk scoring the soil. “If it dries out later, it might crack on the score line, damaging the root,” Ferrie says. “You can prevent scoring by using a cover board on your applicator. Or you can apply the fertilizer in the stem-water zone.” Placing fertilizer in the stem-water zone makes it less dependent on rainfall to move it into the soil. “In 2017, we had little rain after sidedressing our plots,” Ferrie says. “Stem-water placement usually yielded 10 bu. or more per acre than a colter applicator. “With stem-water placement, corn must be bigger when you sidedress,” Ferrie adds. “If you plan to do a stem-water application later in the season, you must apply enough nitrogen early to keep the corn going two weeks past the time you plan to sidedress. This is especially true during the rapid growth stage, when corn needs 7 lb. to 10 lb. of nitrogen per day per acre.” Sidedressing promotes timely application, but in dry conditions the fertilizer might be locked up near the surface until you get rain. “Nitrogen placed in the center of the row, just below the surface, will stay there until rainfall moves it into the root zone,” Ferrie says. “If plants are already nitrogen-deficient, they’ll continue to show a deficiency until it rains. Apply enough nitrogen at the front end of the season to carry the crop beyond sidedressing time, in case the weather turns dry for a couple of weeks.” Limit late-season sidedress treatments to one-third of your total nitrogen application, Ferrie advises. Plants will use that nitrogen for tip-fill. “The other two-thirds of your nitrogen, which is used for stalk-building, should be applied earlier in the season,” he says. If you see an immediate, visible response when you sidedress corn, you probably need to apply more nitrogen earlier in the season. “A visual response indicates the corn wasn’t growing at full speed when you sidedressed the nitrogen,” Ferrie says. “If you apply enough nitrogen early to keep plants growing at a full pace, too much or too little rainfall after sidedressing will be less of a threat.” 4. The last area to weatherproof against is cold temperatures. “In cold soil, just like dry soil, you get reduced microbial activity and reduced mineralization of nutrients, especially phosphorus and sulfur,” Ferrie says. “Even in high-testing soil, phosphorus and sulfur availability will be low until soil temperature reaches and stays about 65°F. Then microbial activity and mineralization pick up again. “Soil temperatures between 50°F and 65°F might last several weeks,” Ferrie says. “But you can get a lot of growth during that period if plants have access to available nutrients.” The solution is to place some phosphorus—and sulfur, if needed—close to the seed as you plant. That will keep plants growing until the soil begins supplying nutrients. “Don’t increase the rate, just modify your placement and timing,” Ferrie says. Regardless if your weather turns wet or dry, or ricochets from one to the other, weatherproofing your fertility program by applying the 4Rs will help ensure crops never have a bad day or go hungry.