LOVELOCK - Although alfalfa production was limited this year because of the lack of irrigation water, it is still important to maintain proper soil nutrient levels to prevent any further stress on the plants.
Determining when applications of nitrogen (N), sulfur (S), potassium (K) and phosphorus (P) fertilizers are needed is also important to maintain alfalfa yield and quality.
The Western U.S. is diverse in terms of climate, soil types, irrigation water need and availability, historical nutrient use and alfalfa production systems.
Therefore, few generalizations hold regarding the timing and location of N, S, K and P deficiencies. Soil and tissue testing are the most reliable ways to assess alfalfa nutrient status and determine fertilizer needs.
Growers must understand what soil test methods (mainly sampling depth and chemical extractants) are appropriate for their area and use interpretations (recommendation tables) developed for those methods. Tissue testing procedures and interpretations are more similar throughout the West, but growers must still match tissue sampling protocols (mainly growth stage and plant part) with the interpretation data.
Nitrogen (N). Alfalfa is a legume and through a symbiotic relationship with bacteria obtains N required for growth from the atmosphere. Most references acknowledge that, during establishment and before bacterial symbiosis develops, a small amount of N is beneficial (20-40 pounds N/acre). Nitrogen application in established alfalfa stands is still controversial. Few of the studies found any positive effects of N fertilization on established alfalfa.
Sulfur (S). Sulfur is an important component of several amino acids and has been shown to influence the yield, protein content, stand density and stand life of alfalfa. Yield responses of up to 300 percent have been reported under severe S deficiency conditions; however, more typical yield responses to S fertilization are in the range of 15 percent to 25 percent. Some soil deficiencies that have been attributed to lack of phosphorus may actually have been cases of sulfur deficiency.
If poor crop growth was corrected by an application of single superphosphate, the benefit may have been due to the gypsum contained in this material. Critical soil test values for sulfur are less than 25 ppm of SO4 or less than 8 ppm of SO4-S.
Potassium (K). More K is removed than any other nutrient except N by alfalfa. A long history of high-yielding alfalfa production has depleted native soil K levels to the extent that most Western States now encourage testing for K and make K fertilizer recommendations.
Recent research from Utah State University showed alfalfa yield responses to relatively high K application rates on low K-testing soils. Due to the high K requirements of alfalfa, frequent and relatively high rates of K fertilizer will be required to maintain high yields once native soil levels are depleted. Critical soil test values for potassium are less than 150 ppm K.
Phosphorus (P). Phosphorus is essential for alfalfa production and likely represents the most common fertilizer input for this crop across the Western U.S. Correlations between soil test P and alfalfa yield are normally very good for the Olsen P test. Various P fertilizer sources are available in the Western U.S.
Research has generally found that conventional dry (11-52-0, 0-45-0) and liquid (10-34-0, phosphoric acid) fertilizer sources are equally effective for alfalfa. Selection of a P fertilizer source should be based on availability and cost per pound of P2O5.
On-farm testing is one way in which alfalfa growers can refine fertility programs for specific situations. An on-farm test might involve a trial to determine whether a higher rate of P or K results in higher yields.
When conducting an on farm test, treat several strips in a field with the new fertility practice and alternate strips with the standard practice. Where possible, treat several test strips in a field and only change one variable (such as nutrient type or rate) for each trial.
Keep individual records of fertilizer applications, soil and tissue test values, and alfalfa yield for the trial to assess whether the new practice improved yield or changed soil test values.
If you need any assistance with setting up a fertility trial, do not hesitate to contact me at the Pershing County Cooperative Extension Office at (775) 273-2923.[[In-content Ad]]
