These conditions are usually indicated by a soil test and may be corrected by liming or applying phosphorus or potassium fertilizer. In addition to showing whether or not liming is necessary, the routine soil test taken prior to seeding shows the phosphorous and potassium soil fertility levels. The calibration of these is provided in Table 6. Note that fertilizer phosphorus and potassium are not needed at soil test indices of 65 or greater for phosphorus and 350 or greater for potassium. Because these nutrients, like lime, are immobile in the soil, the efficient use of applied forms by alfalfa is improved when they can be incorporated in the soil.
Incorporation is practical only before planting.
When annual phosphate deficiencies are no more than 100 lbs. After alfalfa is established, the fields should be soil tested at least every three years to monitor changes in soil fertility and the need to adjust fertilizer rates. The fertility levels of sandy soils will change more rapidly under alfalfa production than with other crops. Soil testing every year is a good practice for adjusting fertilizing needs to sustain high alfalfa yields. Calibrations do not apply to soil tests by other laboratories.