How soon can alfalfa be planted following alfalfa? 

EXPLANATION: Establishing alfalfa following alfalfa is difficult because of several problems, including: 

-- Autotoxicity. 

-- Depleted soil moisture. 

-- Insects and soil diseases accumulated in the first alfalfa crop. 

-- Nutrient deficiency and pH problems. 

-- Drainage problems. 

Many studies indicate that alfalfa can be reestablished successfully following alfalfa. Most reports of problems with autotoxicity are from greenhouse and field studies where top growth of alfalfa was incorporated into the soil and alfalfa replanted immediately. Assuming little foliage was plowed under due to a thin stand, the importance of autotoxicity would be reduced greatly. 

Under some circumstances good producers can have success with alfalfa following alfalfa immediately with special attention. These include: 

--Plentiful rainfall or irrigation between alfalfa stands can alleviate problems with dry soil profiles. 

-- Deep moldboard plowing can assist with removing many of the insects and pathogens from the area where seedlings will grow. 

--Application and incorporation of needed fertilizer and lime before planting back to alfalfa can eliminate nutrient deficiencies. 

-- Drainage problems can be corrected between stands. 

Rotation to other crops allows more time to address these problems. How quickly one can rotate back to alfalfa depends somewhat on weather and how much time is needed to address problems carried-over from the previous stand. Currently, at least a 2-year rotation to another crop is recommended. Increasing rotation time between alfalfa stands minimizes most problems.

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What are good rotational crops with alfalfa? 

EXPLANATION: In Oklahoma there are only a few good rotational crops for alfalfa. The best rotational crops following alfalfa are cereal crops and annual forage grasses. Small grains can benefit from nitrogen released after alfalfa is plowed. Corn and sorghum could also follow alfalfa in those areas where rainfall is adequate or where irrigation is available. 

Yield improvement of cereal crops following alfalfa has long been recognized. Much of this is related to nitrogen (N) fixation by alfalfa. The amount of N plowed down depends on the time of the season and amount of nitrogen-rich top growth at the time of tillage. About 25% of the incorporated N associated with plowing down alfalfa is recovered during the next crop year. 

The crop preceding alfalfa is probably more critical. There should be sufficient time for preparation of a good seedbed. Harvesting a small grain crop in June usually is adequate for seedbed preparation for a September alfalfa planting. 

Alfalfa could also be planted in the fall, following early corn and soybeans. Little time is available, however, to resolve field problems (drainage, fertility), and adequate rainfall must be received to replenish soil moisture. It is frequently advisable to harvest summer crops and wait until the next year to plant alfalfa, thus, avoiding the rush. 

Using soybean, peanut, or other legume species just before or just after alfalfa is usually avoided because they are not effective in reducing build-up of disease organisms.

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Can I thicken up my thin alfalfa stand? 

EXPLANATION: Before reseeding a thin stand, reasons for the thin stand should be evaluated and corrected. 

Seedlings are sensitive to pests that build up in and on old plants in established stands. Seedlings cannot compete with mature plants for nutrients, water, and light. If an older stand has thinned to the point that it is not economical, the stand should be destroyed, and the field rotated to another crop for several years before reestablishing alfalfa. 

Drowned-out spots: There is a temptation to replant "drowned-out" spots. This is justified only if the reasons for the wet spots are corrected. After improving drainage and preparing a good seedbed, alfalfa can be established successfully. Trying to fill in wet spots with new alfalfa, without correcting the problem, usually results in another stand failure. 

Thin seedling stands: There is little danger of autotoxicity problems in thin stands less than a year old. If the reason for a thin stand, from a fall-sown stand, was poor seedbed preparation, late planting, or wash-out (or blow-out), then over-seeding into thin spots in early spring could thicken areas with fewer than 5 plants/ft². Likewise, thin spring-sown stands can be thickened up the following fall if seeds can be placed in the soil 1/4" to 1/2" deep. Again, the problem that caused the original poor stand must be corrected. Even after a few months, soils become hard and weeds encroach, normally resulting in poor seedbeds. 

Don't hope for miracles!! Try to get it right the first time. Thickening up thin stands is rarely completely satisfactory.

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Can alfalfa be established no-till? 

EXPLANATION: Requirements for no-till are similar to conventional seedbed preparation and include: 

-- satisfactory pH and adequate soil fertility. 

-- good surface and internal drainage. 

-- weeds and insects adequately controlled. 

-- adequate moisture for germination and growth of the alfalfa seedlings. 

Additional requirements for no-till planting include: 

-- presence of minimal plant residue on the soil surface so seedling alfalfa is not shaded. 

-- planting needs to be done with a no-till drill equipped to plant alfalfa. 

Any of these conditions are not adequate, then alfalfa establishment by no-till will likely fail, and costly investments for seed, fertilizer, etc. will be lost. 

best chance for success with no-till alfalfa establishment is into small grain stubble in the fall when fertility conditions and drainage problems have already been corrected. The two major problems will be control of weeds during the summer before planting and control of insects on seedling alfalfa. Planting no-till alfalfa into early-planted soybeans would also work, provided there is no left-over row effect. 

No-till establishment of alfalfa into grass sod is possible, but unreliable. Major problems are related to shading of alfalfa seedlings and inability of alfalfa seedlings to compete for soil moisture. The probability of success increases when strips of sod are killed with a herbicide and abundant rainfall or irrigation is received after planting.

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Will herbicide used on a previous crop cause injury to newly-planted alfalfa? 

EXPLANATION: There are "Rotational Crop Restrictions" on many herbicides used in Oklahoma (Table 2). The reason for these restrictions is that there may still be enough herbicide residue in the soil to injure subsequent crops. 

The use of the sulfonylurea herbicides (such as GLEAN and AMBER) on the wheat crop before planting alfalfa has resulted in severely stunted alfalfa seedlings in a number of fields in Oklahoma. This has been particularly evident after dry summers following herbicide application. To be safe, always read and follow crop restrictions on herbicide labels. This includes keeping accurate records as to: 

-- What chemical was applied. 

-- When it was applied. 

-- How much was applied. 

Many examples of alfalfa injury from herbicide carry-over probably occur each year. Often the variety, weeds, or weather are blamed for poor alfalfa stand establishment when in fact it was herbicide misuse, including forgetting when, what, or how much herbicide was applied on previous crops.

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