The benefits of variable-rate fertilizer application. Interview with Kharkiv agronomist Vitaliy Ovcharenko

A fertilization system is an important part of growing any agricultural crop. What’s more, fertilizer-application operations account for a substantial share of the cost of the whole agricultural technology, and as a result, the cost of the final product. Applying mineral fertilizers affects the balance of nutrients in the soil, its fertility, and plant development throughout the whole growing season. That’s why correctly calculating fertilizer doses plays an important role in crop production.

Lately, more and more farmers are starting to take an interest in precision-agriculture elements meant to boost the efficiency of process operations. One such element is variable-rate fertilizer application. This is a relatively new but effective method that improves crop nutrition and takes the technology to a new level.

For the second year running, this method has been successfully applied at the “Rubin” family farm, located in the village of Bilyi Kolodyaz, Vovchansk district, Kharkiv region. Vitaliy Ovcharenko, the farm’s chief agronomist, told us how the switch to variable-rate fertilizer application affected yield and cost optimization.

Agronomist: Vitaliy Volodymyrovych, why did you decide to adopt this fertilization method?

Vitaliy Ovcharenko: When I came to work at this farm three years ago, I realized: to improve profitability, we needed to change our approach to our growing technologies somewhat. As a result, we adjusted our crop-protection system, optimized the acreage under the crops most profitable for us, and started studying what else could boost our efficiency. Variable-rate application, as a precision-agriculture element, looked like quite a promising step.

A.: By the way, what crops do you grow, and what’s the farm’s total area?

V.O.: We’re a relatively small farm – we cultivate 1,500 ha. We grow crops such as winter wheat – 600 ha, spring barley – 200 ha, sunflower – 550 ha, and corn – 150 ha. Wheat and sunflower are our main crops in terms of highest profitability. Accordingly, these crops also take up the largest areas.

A.: And how’s the yield?

V.O.: It varies. It all depends on the weather. Our soils are favorable – mostly deep, medium-humus chernozems. The pH level is close to neutral. But we always have problems with moisture. That’s our main limiting factor.

Average annual rainfall in the region is 350–400 mm. Even so, we often don’t get even that. What’s more, moisture distribution is very uneven. This year was no exception. From May through October there was almost no rain. Rain only came two weeks ago. Before that, wheat seed sat in the soil for about a month and only now started to emerge. So for us the main risks are tied specifically to moisture.

Given the constantly rising cost of mineral fertilizers, variable-rate application, as a precision-agriculture element, is a fairly promising step

On average, for winter wheat under favorable weather conditions we get 60–70 dt/ha. For barley – 45–50 dt/ha. Sunflower delivers around 30 dt/ha. In better years – 35. Corn yield ranges from 70 to 95 dt/ha. But we didn’t grow this crop at all for the previous two years, since we don’t have our own dryer. And drying at an elevator with high grain moisture was fairly costly. Though this year we came back to this crop. We chose early hybrids so they’d have time to fully ripen before harvest. In the end we already harvested grain at 16% moisture.

We can’t boast of any record yields, since we’re in a zone of insufficient moisture. On top of that, we’re still working on improving our technologies and updating our equipment. For example, we still don’t have a self-propelled sprayer to protect corn and sunflower at later growth stages, though from time to time the pest situation in the field already calls for it. Even so, most of our equipment fleet is now new and modern.

A.: What did introducing the variable-rate fertilizer application system start with?

V.O.: The very first thing we did was install navigation systems on our equipment – tractors, combines. Since then, all our operations have run on GPS signal. We installed yield-mapping systems on the combines. But the fertilization system also needed to change. Back then we practically didn’t pay any attention to phosphorus-potassium fertilizers, or applied them in insufficient amounts – just nitroammophoska when sowing wheat. The main focus was on nitrogen.

Given the constantly rising cost of mineral fertilizers, variable-rate application, as a precision-agriculture element, is a fairly promising step

Clearly, if we don’t maintain a nutrient balance, sooner or later it will affect yield, since soil reserves are limited. But we didn’t want to apply an average rate without understanding actual need. So we decided to run a trial soil analysis on one field, to see what our overall situation looked like.

The results showed we had a phosphorus and potassium deficiency. What’s more, the nutrient shortage varied significantly across different parts of the field. Understanding that fertilizers are expensive, especially phosphorus ones, we decided to try variable-rate application technology, to optimize costs and turn the field into a more or less uniform plot.

A.: Did you specifically buy a new mineral-fertilizer spreader?

V.O.: No, we already had a Bogballe spreader at the time that could solve this problem. All we needed was to fit it with the Dynamic Section Control variable-rate system. Then, on the field where the soil analysis had been done and where barley was planned, we decided to run a comparison and find out how much improving the crop’s phosphorus-potassium nutrition would affect the final result.

“Astra” representatives helped us prepare a fertilization map based on the soil analysis results. So, on one part of the field we applied our old technology of just ammonium nitrate, and on the other we applied ammophos and Kalium Makosh on a variable-rate basis, targeting the planned yield. The effect from the additional phosphorus and potassium fertilization turned out to be noticeable. What’s more, we saw that this application method really is effective. First, we managed to avoid overspending on fertilizer. Nutrients were applied only in the necessary amount, also eliminating overlap. Second, we evened out the soil’s nutrient supply across the field. When harvesting, we mapped the plot and noticed there were no longer any significant yield swings. Readings varied within 3–5 dt/ha. If we’d simply applied an average rate across the whole plot, overspending would have grown significantly.

Thanks to optimizing the fertilization system, the farm managed to avoid overspending on fertilizer. Now nutrients are applied only in the necessary amount, according to the needs of the planned harvest

What’s more, even after running two additional operations to apply phosphorus and potassium fertilizers, and factoring in their cost, we still came out ahead thanks to the yield increase. Additional profit in the end came to up to 200 UAH/ha.

So, our experiment let us note the effect of optimizing phosphorus-potassium fertilization and evening out the average yield across the field.

A.: Did you later expand the area under this fertilization method?

V.O.: Yes, the following year we ran soil analysis on several more fields, and in total already had around 400 ha under variable-rate application. On these fields we sowed part of our sunflower acreage, and corn. For disking, again, we applied ammophos and the Kalium Makosh potassium fertilizer.

This year, before sowing wheat on 400 ha, we again applied variable-rate fertilization. Though this time we didn’t run an additional soil analysis, and instead relied on the yield-map results, noting which nutrient and how much needed to be added for the planned harvest.

A.: What working width do you use to apply fertilizer?

V.O.: Usually 24 m, though the spreader can also apply at 36 m. Still, not all fertilizers reach that distance, so we chose the optimal option for ourselves. The spreader’s working speed is 15–18 km/h. So we cover a 100 ha field in 2.5–3 hours.

In general, to apply fertilizer evenly across the full working width, it needs to be good quality. We once had a case where we bought substandard-quality nitrate. As a result, during application the granules were simply pulverized into dust and, of course, didn’t reach the necessary distance. All of this later showed up in the wheat’s development – pale-green patches of unfertilized plants appeared in the field. So we always try to buy from trusted suppliers.

If you compare the classic application method with the variable-rate one, previously, without the Dynamic Section Control system, we had significant fertilizer overspending because of overlaps. On a 100 ha plot we were overspending around one tonne of fertilizer. Now that figure stands at 100–200 kg. And that, again, is cost savings.

A.: And how are things with nitrogen nutrition?

V.O.: Our main nitrogen fertilizer is ammonium nitrate. For sunflower and corn we apply it together with sowing at a rate of 150 kg/ha. We top-dress wheat in spring – 300 kg/ha on frozen-thawed soil. We also add urea at a rate of 10 kg/ha during spraying.

A.: Tell us more about the wheat-growing technology on fields where variable-rate fertilization is used.

V.O.: Wheat’s predecessor for us is mainly sunflower, and on a small area – barley. After harvesting sunflower we do disking in two passes. Before the second disking, ammophos and potassium are applied on a variable-rate basis. Then we sow with simultaneous application of nitroammophoska – 120 kg/ha. All sowing is done using navigation. We always treat the seed with an insecticide and a fungicide. In principle, this protection is enough for us through winter.

From spring, as I already mentioned, we top-dress with ammonium nitrate – 300 kg/ha. Up to now we’ve applied the whole rate in one pass. We simply haven’t had a way to work fertilizer into the soil for a second top-dressing, and leaving it on the surface is risky, since you never know what the weather will be. Still, next spring we want to run an experiment – apply the full rate in one pass on one part of the field, and split it into two applications on the other, doing the second nitrate top-dressing via navigation in the row spacing, which for us is 20 cm. We’ll see which method works better.

Then, after early-spring top-dressing, we harrow to seal in moisture and protection begins. Over the season we run two to three treatments. For example, this year there were two: the first – herbicide + insecticide + fungicide, the second – top-dressing + fungicide + insecticide. We use only quality products with long-lasting protective action for all of these. Seed treatments included.

We also make yield maps on all fields. Though for now we only use the ones with variable-rate application. But going forward, I think, we’ll switch all our acreage to this fertilization method.

A.: What yield target is the technology usually designed for?

V.O.: For wheat we plan for 80 dt/ha with the corresponding fertilizer rate. For corn we plan for 90 dt/ha, sunflower – for 35 dt/ha.

A.: Did introducing variable-rate application affect your crop-growing costs?

V.O.: Yes, since we started running additional phosphorus-potassium fertilization operations. Though they paid for themselves thanks to the yield increase.

Today, on average, a hectare of wheat costs us 11–12 thousand UAH, sunflower and corn – within 15 thousand UAH/ha. That is, at current prices, profitability for us starts at 40 dt/ha for corn, 20 dt/ha for sunflower, and 30 dt/ha for wheat.

The switch to variable-rate fertilization itself doesn’t require large costs. If you have the right spreader, you can simply fit it with the necessary system – and that’s it. But without a properly conducted soil analysis and practically grounded interpretation of the data, you can’t get any effect from this fertilization method.

I believe variable-rate fertilization is already a practical necessity, one that lets you get maximum economic return on the resource invested in the field, especially if your fields are patchy. Our own production results confirm this method’s effectiveness. Even so, we’re not stopping at just applying fertilizer with a spreader, and we’re already looking into variable-rate fertilization technology applied directly into the soil.