When you applied your fertilizer this spring, you probably hit some sticker shock – prices are way up. I can’t help you with the high prices (my magic wand is in the shop) but I have collected some best practices for NPK application and use to help cut the bill.
Let’s hit nitrogen first. Some midwestern farmers are making good savings on their nitrogen bill by using N-Serve and greatly reducing their application of liquid nitrogen – to as low as 20 to 25 pounds per acre. N-Serve application used to be limited to anhydrous tanks, but new injection technologies make it possible to directly inject the N-Serve along with the nitrogen application, using a Sidekick to control the flow. Mapping technology allows you to target the N-Serve to the exact full or partial field where it’s needed, although many farmers just apply it across the entire acreage.
No-till farmers already know that losses of liquid nitrogen can reach 20% due to volatilization under the right conditions. These farmers have built an applicator that allows them to apply NH3 subsurface. Not only is the NH3 cheaper by twenty or thirty cents a pound, but the subsurface application greatly reduces loss to environmental conditions.
A slightly higher tech-approach is the use of ESN, a fertilizer mix that wraps urea pellets in a polymer that degrades slowly over time. The ESN polymer is more expensive than straight nitrogen by about ten cents a pound, but the savings come from the fact that you can use somewhat less of it. The polymer protects the N from leaching during the heavy spring rains, but is degraded to the point of releasing most of the nitrogen right around the time that plants are hitting their peak growth cycle. It’s like doing a side dressing in advance.
With phosphorus, oftentimes it’s a question of too much, rather than too little. Phosphorus runoff causes any number of problems with local water sources, and the last thing you need is to have environmentalists yelling at you. Fortunately it’s not too difficult to manage your phosphorus situation. The first step is to know your yield goal for your acreage. Second, calculate your P requirement to hit that yield. Third, test your soil and see what you’ve already got – the odds are pretty good that you have enough P already and don’t need to add any at all. If you are low, then apply the P in the most efficient manner possible. One efficiency booster – add zeolite to your soil. Naturally occurring P, and any that you apply, will bind to the zeolite and be released naturally in response to plant action over the course of the growing season.
If you do need to add P, then add it in the right place! Surface application, unless you’re growing perennial forage, is a huge waste, and contributes to P runoff and eutrophication. Apply P to the root zone only, either at planting time or using subsurface application. If you are using manure as a fertilizer source, be aware that adding enough N to meet your yield requirement is almost certainly going to overload your soil on P. That won’t hurt your crops, but it will make your runoff a problem for your neighbors, and you’ll need to take some extra care in managing your water.
Given the ubiquity of P in the natural environment, however, it’s more likely that you won’t need to add much if any – particularly if you preserve what you have. Soil management technique is the way to keep the P you have in the ground, instead of running out into the wastewater ditch. Any number of land management techniques can help with that – conservation tillage, conservation cover, conservation cropping sequences, delaying your seed bed preparation, adding a grass filter strip or waterway, contour farming, strip cropping, terracing, a sediment control basin, even a constructed wetland – these are good for the environment, AND good for your fertilizer budget as well.
Potassium (K) is of course a critical fertilizer, and one of the most important things to be aware of in K application is the target crop. K uptake rates vary wildly by crop – from 120 pounds an acre for soybeans, to 400 pounds an acre for alfalfa. Be aware of the K need that your particular crop has, and adjust your application accordingly. Also bear in mind that your N uptake rate is controlled by the K level in the plant – a deficiency of K can cause an effective deficiency of N, even if you’re drowning your crop in NH3. K also regulates P uptake – so be sure to get that K level right.
Like phosphorus, potassium levels in the soil are often high enough already, so soil testing is definitely worth the minor investment, especially if it saves you an application. In addition, as with phosphorus, improving your K cycling on the farm can preserve the element and prevent the need for future application. As with P, a zeolite admixture can help bind the nutrient and prevent runoff and leaching, leaving plenty of K available when the plant starts to really draw on it. However, when you do need K, there are some techniques you can use to manage the cost.
Common potassium fertilizers tend to have a high salt index – don’t place them near seeds or seedlings, especially in sandy soil or with high levels of application. Instead, a band three inches to one side and two inches below your seedbed will provide plenty of K for developing plants without injuring seeds or transplants. Split application is recommended for crops with long growing cycles, because plants will uptake more K than they need if it is available, possibly reducing levels below the critical point later in the season. If you are using no-till or low-till, you will need to increase the K application because liquid K applications tend to stay near the surface; you won’t need a higher level if you’re fertilizing corn, however, as corn’s extensive shallow root system will absorb what it needs.
I’ve only hit some of the high points; there is a lot of literature and information out there to help optimize your fertilizer application this year. Good luck!
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