Fall 2005

Northcentral

Many in agriculture are concerned about higher fertilizer prices. Here are a few key concepts to remember when thinking about a phosphorus (P) and potassium (K) fertilization program.

• Soil testing is the best tool for indicating whether or not a soil should receive fresh supplies of nutrients. It is a worthwhile investment. Remember that if a soil sample represents a large area, there may be areas within the field with much lower soil test levels than the overall result might indicate.
• Soils with higher soil tests do not need additional broadcast applications of nutrients in the short term. But remember to monitor crop removal rates and keep testing the soil over time to ensure that soil test levels do not drop lower than desired. Soils with higher initial tests tend to drop more rapidly than soils with lower tests.
• In some states, addition of nutrients in a band applied near the seed at planting (termed starter fertilization) provides early and late season benefits, even on higher testing soils.
• Management of P and K depends on land use. Short-term rental ground may be most profitable to the renter if kept at lower, more responsive levels. However, overall yield levels may suffer. Land that is owned and cared for with a long-term strategy is best built to higher levels, where the risk of nutrient shortages is minimal and the probability of higher yields is greater. In lean years, these fields can be built more slowly or maintenance applications made until economic conditions improve.
• Use manure sources wisely. Whenever possible, apply manure to fields that need supplemental P and K supplies. Get the manure tested and keep good records of where in the field applications were made. This will allow you to determine how much of each nutrient was applied and where it all went. If you occasionally scrape pits, remember that there is a good supply of P in the manure solids that collect at the bottom.

It is important to recognize that there is no one strategy that fits all scenarios, even on one farm. Accounting for all sources of nutrients will ensure that purchased nutrients are used only where needed.

Winter wheat has performed well in many parts of the region. For next year, assure yourself a good start by planning for the fertility needs of the crop to be seeded this fall. Nitrogen (N) and phosphorus (P) are important components of a starter to ensure a healthy stand. Wheat can be profitable, as well as an excellent soil builder in the rotation.

Manure applications following harvests of cereals and silage corn should be guided by soil tests and manure nutrient analysis. Rates should be appropriate to supply the soil's needs for P, K and organic matter. Avoid wasting N by ensuring a cover crop grows to absorb what is released from the manure.

Soil buffer power is the factor which makes a big difference between mobile nutrients like N and immobile nutrients like P. The capacity of the soil to re-supply P to the soil solution after crop removal defines its buffer power. A soil with a high buffer power is fast to maintain P in solution around the plant roots. Alternatively, a soil with a low buffer capacity is not as capable of re-placing soil solution P after crop uptake.

Routine soil tests do not measure the buffer power of the soil, but they do measure the nutrients in solution and a fraction of the nutrients that may come into solution. Soils have different properties that affect their P buffering ability and the rate of P replenishment. Amount and type of clay minerals, organic matter level, other soil constituents, and fertilizer P history are all important contributors.

Buffer power increases with increasing clay and organic matter content, as does the ability to influence soil test P with fertilizer additions . Soils with high buffer power (high organic matter and clay) need more P fertilizer to increase their soil test level than soils with low buffer power (high sand and low organic matter). Typically, 14 to 22 pounds of P2O5 per acre is required to increase a P soil test by 1 part per million (2 pounds per acre).

Preparation for wheat planting is well underway. Growers and their advisors should remember that phosphorus (P) nutrition of wheat is a critical factor in achieving optimal yield. Although only small amounts of P are taken up by wheat early in the season, it nevertheless plays a major role in early plant development and determination of attainable yield potential. During the first few weeks, P supply increases the proliferation of roots as well as the initiation of tillers. An insufficient supply early in the season creates irrecoverable yield losses. Phosphorus shortages later in the season have less impact than those encountered earlier. Although higher soil fertility levels are important for season-long P nutrition, early season P supplies must be accessible to the limited root system of the young wheat plant. For this reason, P placed near the seed at planting (starter P) has proven effective, especially in cold soils. The response of wheat to low rates of starter P is often referred to as the “pop-up effect”, and is marked by improved leaf and root growth, tiller formation, and yield. Some research has indicated that starter P can provide benefits even at higher soil test levels, probably because of its superior positional availability. Bottom line… make sure wheat planted this fall has sufficient available P so that yield potential is not compromised. Also, remember that a well-managed fertility program must consider the complete nutritional needs of wheat.

Asian soybean rust has been detected primarily in sentinel plots, and fortunately, only in a few production fields to date. Several of the sentinel plots have been destroyed to limit the potential for spread of the rust spores. The map pasted here depicts the counties in the Southeast region where soybean rust presence has been confirmed, as of August 10, 2005. The hurricane season, so far, has not dispersed the disease as widely as was feared possible. Vigilant scouting by Certified Crop Advisers, independent consultants, industry representatives, county Extension agents, and farmers continues. Disease detection and control treatments in the Southeast region may help limit the potential for spread to fields in the upper Midwest.

Extension workers in several states have reported increased symptoms of potassium (K) deficiency this summer. Agronomists in Kentucky have pointed out that soil test K levels may not be as high as some farmers thought, after the exceptional yields produced the last 2 years. Removal of K with past crop harvests, soil compaction, a developing good yield potential, and recent dry weather are factors that may have contributed to the symptoms. All farmers should be encouraged to have soil samples collected at least every 2 years, to track trends in fertility over time. Frequent sampling can identify problems that can be corrected before the next crop.

Continued storms and showers in Florida and Georgia hampered some pesticide applications on peanuts and cotton, and made hay harvest challenging. Vegetable production and peanut yield potential is being affected by increased diseases. Watermelons are ripening and pecans look good. Rice harvest has begun in southern Louisiana and initial yield reports are favorable. Corn is drying down and harvest has begun in some states, but much of the corn is just approaching the dent stage. Wet and cloudy weather in the more eastern states has caused some shedding of cotton squares and bolls, while drought is resulting in fruit abortion in parts of Mississippi, Tennessee, and Arkansas. In Mississippi, early maturity soybeans were beginning to shed leaves as they mature. Some April-planted Maturity group IV soybeans were harvested in Arkansas.

According to the Florida Ag Statistics Service, citrus growers in some of the southern Florida counties are pumping excessive water out of their groves. Fertilizing, spraying, and care of hurricane-damaged groves and young trees have occupied grove managers.

Pastures in Arkansas, Missouri, parts of Tennessee and Kentucky have suffered from prolonged heat and lack of moisture. Some ranchers have reportedly begun to liquidate their stock because they can not afford to purchase more hay. The heat is also taking a toll on livestock weight gains.

There are rumblings among farmers… and some fertilizer sales people are worried that farmers may balk this fall in purchasing needed plant food… because of the higher fertilizer costs. The recently signed U.S. trade agreements, foreign competition, international trade pressures to abandon commodity support programs, and the U.S. administration’s intent to phase out subsidies has many farmers in the southeast concerned about their future. There is speculation that some farms will be sold and that the better managers will purchase or rent the available land, such that the total acreage farmed may not change greatly. It seems likely that fewer farmers will be making larger purchases and sweeping management decisions. Many farmers who are good managers know the value of maintaining soil fertility to protect yield potential, since they have no influence over crop prices.

Given the essential role of soil testing in making correct management decisions, collecting proper samples is critical. This means taking samples from representative areas in the field, identifying special management zones (such as those receiving manure), and accounting for differences in the landscape. Taking good soil samples will take the guess work out of management decisions and help get the most return from your fertilizer investment.