EXTREME WEATHER: Does it call for extreme soil fertility measures?

As if the extreme weather conditions aren’t wielding enough damage on the 2011 crop, farmers must also consider the longer-lasting effects that severe drought and extended flooding could have on soil fertility affecting next year’s crops. “Some areas were so affected by drought that seed never even germinated, while flooding in other areas may have stalled out planting altogether and resulted in significant nutrients losses,” says Dan Froehlich, manager of new product development for The Mosaic Company. “Crops in ‘good to excellent’ condition do exist this year but in many regions are rare.”

Research shows that a key strategy for helping crops through periods of stress is maintaining proper soil fertility, says Dr. Paul Fixen, senior vice president at the International Plant Nutrition Institute (IPNI), Brookings, S.D.

“As we prepare to face more extreme weather events in the future, it becomes even more critical for growers to get their nutrient houses in order,” he says. “Balanced soil fertility can be the boost that puts an ear of corn on the stalk in a tough year.”

Crops simply have a better shot at recovering from wet or dry conditions when growers have routinely practiced the right source-rate-time-place approach to nutrient management, he says.

Regional Soil Fertility Considerations
Residual nutrient availability following this year’s wet and dry spells must be carefully considered when making soil fertility management decisions this fall and spring. While such decision are site specific and should be based on soil tests, below are regional weather snapshots and soil fertility considerations.

In the Southern and Central Great Plains, IPNI regional director Mike Stewart says severe drought has led to lower yields and complete crop failure in large swaths.

“Where yields have been reduced or crops have failed, farmers will need to consider that some fertilizer applied in 2011 may be carried over into 2012,” he says. “On the other hand, some corn and sorghum that was initially planted for grain was harvested for silage or baled in anticipation of grain crop failure. In this situation, drought may result in more removal than expected and therefore a need for greater fertilizer inputs going into next year.” 

Soil testing prior to next season will be important, he says, including testing for N (nitrate-N, 2-foot sample depth).

The situation in the Southeast is similar, says IPNI”s regional director Steve Phillips: “While we have not had the extent of crop failure that Texas and Oklahoma have seen, our dryland corn yields will be down. However, we would not expect the residual N that western states might find as a result of lower yields.” The moisture and flooding that have plagued the Northern Great Plains Region this year have presented a different set of soil and nutrient management challenges, says Tom Jensen, IPNI regional director.

“Some excessively wet and flooded unplanted fields are now being summer fallowed until the fall when a winter cereal may be planted,” he says. “Often these fields had fertilizer applications applied either the previous fall, or in some cases before the planned planting operations that the moisture prevented. There is always a question as to what happened to nitrogen in the previously applied fertilizer.”

Soil sampling and analysis can determine whether nitrogen has been lost due to denitrification, and if a portion of the applied nitrogen was lost, it is important to know what is remaining, he says.

“Many of the fields that were eventually planted, albeit later than normal, are benefiting from adequate P and K applied in a starter blend that will help the crops to mature before fall frosts,” Jensen adds.
Weather in the Corn Belt has been highly variable, says Dr. T. Scott Murrell, Northcentral director for IPNI. “Different areas within a single field may have seen both flooding and drought this season. A year like 2011 reminds us how weather can impose a great amount of variability on crop growth and development.”

Weather extremes will come and go, he says, but when it comes to nutrient management approaches, there are a few things growers can do to prepare for the worst that Mother Nature can dole out:

Soil Fertility Strategies for the Worst (and Best) of Times

• Right time: Apply nitrogen (N) close to the time the crop needs it. Pre-plant and side-dress applications accomplish this goal. Fall applications run the risk of losses over the winter and early spring, especially when precipitation is high prior to planting.
• Right place:
• For corn and wheat, apply part of the recommended rates of nutrients with or near the seed at planting. Subsurface applications near the seed are positioned well for uptake early in the season, and in some cases such a placement can hasten crop maturity, resulting in lower grain moisture at harvest.
• Next year, band phosphorus (P) near the seed at planting on soil areas that were flooded for a week or more this year or were fallow. Both fallow periods and flooding reduce the population of beneficial mycorrhizal fungi that the crop typically counts on for providing a significant portion of its P needs. When populations of these fungi become lower, P nutrition can suffer, and banding P near the seed is the best approach for at least partially making up the difference.
• Get nutrients below the soil surface. Both fertilizer and manure have a portion of their nutrient supply readily soluble in water. When intense rainfall leads to runoff events, soluble nutrients can move off of the field and into surface waters.
• Right rate: As finances permit, build the phosphorus (P) and potassium (K) fertility of the soil profile. Broadcast applications followed by incorporation with occasional deeper placement (6 to 8 in.) will keep nutrients better distributed vertically. When drought or just drier weather hits, nutrient movement in soils becomes limited. Higher fertility levels help compensate, keeping the plant better fed when water movement in the soil becomes limited.
• Implement erosion control practices where needed. Erosion removes more than just soil. It also removes the P and K bound to it. Keeping soil in its place in the field ensures that nutrients remain in their place too.
• Apply agricultural lime to soils with high reserve acidity. Soil pH affects the availability of many nutrients as well as root growth and development and nodulation. Ensure that soil pH is within the target range for the crops to be grown.
• Limit soil compaction. Soil compaction does many things to adversely affect nutrient and water movement in soils. It also limits root development and rooting depth. When soils become dry, compacted areas are often the first to show signs of both water and nutrient stress.