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Soil fertility tips in high-cost environment

As the costs of ammonium nitrate and phosphate reach and exceed 70 cents and 80 cents per pound, respectively, most farmers are seeking ways to increase efficiency or implement new – and even old – technology.  Following are some pointers from soil fertility experts in the South:

  • Testing soil.  According to Larry Oldham, an Extension soil expert at Mississippi State University, all farmers should be on a soil testing program.   “If you use a land grant university recommendation system, the result is going to be based on the sufficiency philosophy — to supply enough to grow the crop during a growing period. If you go on replacement — X bushels will replace X pounds of potassium (K) and phosphate (P) — this can lead to a higher application rate.”

    According to Charles C. Mitchell,  an Extension agronomist at  Auburn University, if potassium (K) and phosphate (P) levels are already elevated, these nutrients do not need to be applied for maximum production, as there is already sufficient in the soil to meet crop needs..

    Keep in mind that soil tests do not reveal the total amount of K in the soil – usually much more than test results show – and that it does become available in the soil over time.  Soil pH should be maintained for maximum availability of applied and native K and P.

  • Avoiding nitrogen losses. “There are volatilization issues when urea is used in hot weather, on heavy crop residues or forages, on high-pH soils, and in dry weather,” said Mitchell. “However, it could still be incorporated, irrigated in, applied just before a rain, used on bare soil or injected.”

    Commercial additives known as urease inhibitors are also available, which help to bring down losses due to volatilization.  It is useful to compare prices to determine if the effects of such inhibitors are worth the additional cost.  As Oldham explains,  “We still like split applications of nitrogen on corn.  We think it might be a little more efficient. We like to use the liquid sources in Mississippi. Remember that UAN solution, a mixture of urea and ammonium nitrate, has the potential to volatize if we don’t get it in the ground soon after application.”

  • Using legumes.   Hairy vetch, common vetch, or crimson clover (i.e. winter annual legumes) can offer 90-150 pounds of nitrogen per acre to summer crops.  Mitchell states, “This has been demonstrated for over 110 years by Alabama’s old rotation experiment (circa 1896). In fact, cotton with only winter legume nitrogen has produced as much or more yield as cotton with 120 pounds of nitrogen per acre per year and no winter legume (it averaged over 2 bales per acre of non-irrigated cotton the past 10 years).”

    Using legumes not only provides nitrogen, but it also can help build organic matter in the soil.  Forage quality is improved by using either perennial or winter annual legumes in permanent, summer grass pastures; this also provides sufficient nitrogen for three tons of dry-matter production.  It is worth noting that this might not be enough nitrogen to maximize production in bermudagrass hayfields, but it may allow farmers to make one or two fewer applications of fertilizer nitrogen.

  • Using poultry litter. “If you need the P and can’t afford DAP or triple superphosphate, try poultry litter,” said Mitchell. “I’m told there are places where you may still be able to get it spread for around $30 to $40 a ton but it won’t stay at this bargain price for long. The farther it has to be transported, the more it will cost, but I’m told some row crop farmers are paying around $60 per ton for it and glad to get it.”

Most producers are having a difficult time acquiring enough poultry litter as it has gained in popularity.  However, compared to commercial fertilizers, the price poultry litter is still a bargain.  Most poultry broiler litter is , at minimum, a 3-3-2 grade fertilizer (60-60-40 pounds of N-P2O5-K2O per ton). These nutrients are usually valued at over $100 per ton at today’s commercial prices.

Mitchell explains that  poultry litter “has the most fertilizer value the day it comes out of the chicken house. Whatever you do to it is adding costs. So if you pelletize it, it makes it easier to handle, but you haven’t added any value to it.”  It is important to keep in mind that the analysis (percent N-P-K) in raw poultry litter very widely, while pelletized or processed litter offers much more stability.

Challenges with availability of poultry litter may be caused by “poultry houses just not cleaning out the houses fast enough,” according to Mitchell. “One reason is that chicken houses are paying more for shavings which are removed with the chicken litter.”  Mitchell adds that a number of cotton producers in Alabama are hauling poultry litter 150-200 miles to their farms, which was unheard of a decade ago.

Oldham has explained that there is a cost-share assistance program for poultry litter transportation, under EQIP, but issues still exist with respect to getting sellers and buyers together.

Your local Extension office is a good source of information regarding best management practices in poultry litter application.   In the short-term, many crops can withstand temporary increases in fertility costs, according to Mitchell: “My research shows that if you’re growing crops such as soybeans and peanuts, they don’t mine much P and K.”

It is important to calibrate your equipment well, so that fertilizer is applied only in the desired locations and amounts.  As fertilizer supplies have been unstable at different times throughout the year, Oldham suggests that maintaining a positive relationship with fertilizer suppliers is key. “Suppliers are not wanting to invest a lot of money in inventory and have someone say he can’t afford to buy it.”

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