At a recent conference, Ward Laboratories president Ray Ward answered farmers’ questions about making the most of soil nutrients in no-till systems.
Among other things, Ward’s lab in Kearney, Neb., recently developed a biological test based on soil phospholipid fatty acid (PLFA) profiles that could help no-tillers determine if they’re making the right management decisions to promote a diverse, active soil-microbial community.
Q: Can both nitrogen and increased microbial activity from cover crops be measured in soils and assigned credit?
RW: “There are tests we use to measure cover-crop nitrogen to know how much to reduce the nitrogen for the following crop. We can also measure microbial life, but I don’t know how you interpret that right now.
“Harvest one square yard of cover crop, stuff it in a plastic garbage bag and send it to us, and we’ll measure the nutrients and calculate it to an acre basis. We’re saying 50% will be available for the next crop.”
Q: If cover crops are fertilized, will they give nutrients back to the crop?
RW: “They will, because it’s going to keep nutrients up top. As that cover crop decomposes, those nutrients are going to be released.
“During summer, the cover crop will be decomposing and releasing nutrients. We want broadleaves in the cover crop because they have a lot more nitrogen. That makes the carbon-to-nitrogen ratio narrow enough to release nitrogen.”
Q: Does your lab test for living organisms in the soil?
RW: “We can do the analysis, but right now, it’s up to you to make the interpretation — or find a microbiologist to do that. We have some expertise on staff to help us understand what’s going on.
“The idea of biological tests is to make comparisons. You compare different cropping systems and see which is best. Sample when the plants are growing — wheat up to tiller stage, corn knee-high or after. Take a 0-to-8- or 0-to-6-inch sample with 10 cores mixed together.
“Use a clean bucket and soil probe with no carbons at all — no WD40. We use WD40 for taking soil samples for fertility, but we can’t do that with biological because we’re measuring PLFA — phospholipid fatty acids — and oils are fatty acids.”
Q: What’s your opinion on sulfur and chloride application for wheat?
RW: “In no-till residue management, we’re trying to build organic matter in the soil. If we’re building organic matter, we’re sequestering all the nutrients. So if we use sulfur out of the organic matter, we aren’t building it.
“We tend to be sulfur deficient, since there’s less sulfur in the atmosphere. If you’re applying 100 pounds of nitrogen, you’ll probably need about 10 pounds of sulfur.
“On the chloride, we’re seeing lots of low tests. We’re frequently recommending 20 to 30 pounds of chloride, but I think you’d get by with 10 in most cases if you want to use it every year.
“Then there’s the question of when plants need nutrients. There are three mobile nutrients — nitrate, sulfur and chloride. We need to apply these annually because of leaching, and it’s best to apply them when the plant starts to grow fast because that’s the period of biggest nutrient demand.
“From tiller to jointing to the boot, wheat grows pretty darn fast. That’s when it’s taking up all those nutrients. By full tiller, you want your nitrate, sulfur and chloride present to build that plant. By flag leaf, we have about 50% of our dry matter produced, 70% to 80% of our nitrogen and phosphorus taken out, as well as about 85% of the potassium.”
Q: What source of chloride should be used on corn?
RW: “The first is the dry product, potassium chloride (0-0-60). If you need potassium, you get chloride with it. Ammonium chloride liquid and ammonium chloride dry are the other products that work well.
“Kansas State University work shows chloride response on corn is just as good or maybe better than on wheat. Milo responds well, too. We don’t have much chloride in soybeans, so I wouldn’t use it for that crop.”
Q: When is it best to sidedress corn?
RW: “On corn, I would do that in the five- to six-leaf stage. By the time it gets to eight leaves, you’re probably getting too late. You’re also at the mercy of the weather. If it starts raining and you haven’t applied, you’re in trouble.
“As soon as you can row the corn — if you have a lot of acres to get over — you should start. The immobile nutrients are in the soil. Nitrate, sulfate and chloride are anions. They are negatively charged and just move down with the water.
“But the immobile nutrients — potassium, calcium, magnesium, zinc, iron, manganese, copper — are positively charged and they hold on. Phosphorus attaches to aluminum or calcium ions and doesn’t move very far. Immobile nutrients should be applied before or at planting. If you sidedress phosphorus or any immobile nutrient, you’re fertilizing for the next crop.
“We’ve kind of lied to farmers over the years in saying phosphorus doesn’t move in the soil. It does — a little. At South Dakota State University, I had an experiment in the 1960s. We put on a high rate of phosphorus in ’63, ’64, ’65 and ’66, and in 1989 they sampled that soil and the phosphorus was moving down into the 12- to 18-inch zone. So it does move over time.”
Q: What options are out there for sulfur sources?
RW: “The liquid is ammonium thiosulfate, 12-0-0-26S, and it should never be put on with seed. Thiosulfate will kill plants. Keep it away from seed and don’t spray it on plant tissue.
“For dry sources, you have ammonium sulfate. It’s very soluble with 21% nitrogen and 24% sulfur. K-Mag or Sulfa Mag is about 22% potassium, 12% magnesium and about 22% sulfur. And then there’s gypsum at about 19% sulfur. All are good soluble sources.
“The other is elemental sulfur — the yellow flakes. They usually grind it into powder and granulate it. When it goes on soil, the microbes can go in the pores and convert sulfur to sulfate. That takes time, though, and it will be slowly released through the summer. If you need sulfur and want to use elemental, put one of the other sources with it at about half-and-half and you’ll have late-season sulfur, too.”
Q: How can the protein content of wheat be increased?
RW: “Nitrogen applied before the head emerges increases yield, but after that additional nitrogen usually increases protein.
“If you apply 2.4 pounds of nitrogen per bushel, subtracting the soil nitrate, that’s what you’d apply for yield. To increase protein, come in at flag leaf — or a little later — and apply 15 or 20 pounds of liquid. You might burn the leaf some, but that’s what’s going to increase protein. Urea won’t burn the leaves like UAN, though.”
Q: Do you credit organic matter?
RW: “No, I do not. If I take 1 pound of nitrogen out of the organic matter, I destroy 20 pounds organic matter. You cannot build organic matter without building nitrogen and other nutrients.
“I’ve had guys tell me they could increase organic-matter content by 1% in 4 years. My first question is, ‘Where do you get 1,000 pounds of nitrogen?’ Each percent of organic matter contains 1,000 pounds organic nitrogen in a 7-inch depth of soil.
“Organic matter of the soil dropped because the pioneers used it to supply nutrients to their crops. Now we’re trying to build it back, so we have to sequester the plant nutrients back into the organic.”
Q: Will lower per-bushel nitrogen rates rob organic matter?
RW: “I use 0.75 pounds of nitrogen per bushel of corn as crop removal, and that’s 10% protein on a dry basis. Most of our protein in corn is 9% on a dry basis, which would be closer to 0.7 pounds of nitrogen removed per bushel.”
“If someone says he gets by with less than that, the first question is, ‘What’s your protein content?’ If his protein content is high, then it’s getting the nitrogen out of the soil. The plant gets nitrogen somewhere, or yield suffers.”
“If you’re getting by with less nitrogen, you’re robbing somewhere else — or you have a big carryover of residual nitrogen. If you apply 0.8 pounds of nitrogen per bushel and grow maximum yields, you’re doing a great job with your soil. But if you’re getting by with less nitrogen, you’re stealing from organic matter.”
Q: With soil testing, how deep should the core sample be?
RW: “We ask customers to report depth, so we acknowledge that on the recommendation. I prefer the 8-inch depth.
“Whatever you take, be consistent. If you take a shallow sample, nutrient distribution is highest at the top. As it goes down, it gets lower. If you take just the top 3 inches, you have higher tests and your recommendation is going to be lower.
“You might like that, but the fertilizer guy doesn’t, so he might go 0 to 12. To be consistent, I’d like to see that 0 to 8 all the time so we know we’re making the same recommendation.”
Q: What about using zinc sulfate on low-testing soils?
RW: “Zinc sulfate is 33% to 36% zinc. It’s soluble and that’s the zinc fertilizer you should use. I really prefer to broadcast my zinc sulfate to raise the zinc soil tests up to 1 part per million.
“We have too many in the 0.3 to 0.2 range and it takes 1 pound to raise the zinc soil test one-tenth part per million. So if you’re at 0.3, you need 7 pounds. With 33% zinc, that would be 21 pounds of zinc sulfate and you can mix that with 11-52-0 or another fertilizer and broadcast it.”
Q: With growing corn, when is the right time to apply nitrogen?
RW: “On dryland, do it between the three- and five-leaf stage — or if you’ve got lots of corn, start a little earlier. On irrigated corn, I would do the same thing on sidedress, and then put a third of the nitrogen through the pivot when the crop is growing rapidly — eight-leaf to tassel. Put on most of it then and save the last 20 to 25 pounds for when the silks turn brown.
“About 25% to 30% of the plant nitrogen is taken up after tasseling.”
Q: What about soil tests for nutrient recommendations compared to tissue analysis?
RW: “The plant analysis won’t tell you much about how many pounds to put on. I could do that for nitrogen and maybe for sulfur — the mobile nutrients — but for the immobile nutrients, I cannot give a recommendation. I would always use soil tests as a basis for how much to apply, and the plant analysis to see if you missed something.”