FERTILIZATION OF LETTUCE

A soil test is highly recommended in the spring. A good soil test will eliminate guessing on soil nutrient test levels and will easily pay for themselves in fertilizer savings or better crop yields. A top soil to 8-10" is recommended. One important thing to remember when fertilizing lettuce is that it's a crop with a limited root system and although it is not a particularly high users of fertilizer, when the lettuce needs certain elements they have to be readily available. Therefore the correct amounts of fertilizer and there timing and placement is very important for a successful lettuce fertility program.

NITROGEN

Total Nitrogen Requirement = 120 to 170 Units/A Use higher figure if a lot of leaching is expected of nitrogen.

Use a Nitrogen budget in a limited way to determine what the actual field will need. Lettuce with its limited root system cannot take advantage of many residual forms of nitrogen in the soil. Divide the soil and water test residual levels by 1/3 for the final figure for the nitrogen budget.

Nitrogen requirement: ___________________________

Surface soil Nitrate-N / 3: _____________________________

Organic Matter N Release / 3 : _________________________

Manure N Release / 3 : _______________________________

Irrigation Water Nitrate / 3 : ___________________________

NITROGEN FERTILIZER REQUIRED:_______________ (Lbs./A) This result shouldn't be much under 110 units/A

(Subtract the various nitrogen forms available from the nitrogen requirement to get the nitrogen required)

Organic matter release in the SLV = 10 x % Organic Matter in topsoil which is usually 10 units nitrogen/A.

In Warmer areas the O.M. release will be 20 x O.M.% or even 30 x O.M. %.

Irrigation well water supplies some nitrogen, but varies with location and depth of well. Use the following table to interpret water test results to estimate the nitrogen supplied by the irrigation well water.

Nitrogen Credit from Irrigation Water
No3N-N in Water	Water Applied (inches)
ppm	6	12	18	24	30
1	1	2	4	5	7
2	3	5	8	11	14
3	4	8	12	16	20
4	5	11	16	22	27
5	7	14	20	27	34
6	8	16	24	32	41
7	9	19	28	38	47
8	11	22	32	43	54
9	12	24	36	49	61
10	13	27	40	54	67
12	16	30	45	60	75
14	19	38	57	76	95
16	22	43	65	86	108
18	23	49	73	97	122
20	27	54	81	108	135

Calculating release of nutrients from manures is always tricky and is best done with experience and a nutrient test of the manure to be used. Soil temperature can influence release as well from year to year. Use the table below to estimate nutrient content on a dry basis of various manures.

Manure	Total N	Ammonium N	Phosphorus	Potassium	Sulfur
	Lbs./Ton
Non-Composted Poultry
Turkey	35	4	53	37	6
Fresh Broiler	78	6	51	53	9
Fresh Layer	79	8	125	67	16
Aged Layer	43	9	164	79	14
Non-Composted Dairy/Steer
Fresh Dairy separator solids	43	1	17	12	10
Fresh Dairy corral scrapings	47	2	26	141	12
Aged Dairy separator solids	41	1	13	8	9
Aged Dairy corral scrapings	26	5	31	66	8
Composts
Broiler	38	2	86	50	11
Dairy	27	1	27	57	9
Dairy/Steer	33	0	17	51	9
Dairy/Poultry	34	2	39	75	29

Nitrogen Timing: Lettuce responds to splitting nitrogen applications. Applying too much at the beginning can result in high leaching losses below the root zone. Its best to band or use directed spray to apply fertilizer to only the beds as any fertilizer applied to the furrows will not be utilized since virtually no lettuce roots will be found in the furrows. At planting apply the nitrogen that comes with most phosphate fertilizer sources or about 20 - 30% of the total amount. This can be banded or sprayed on the beds. The rest of the fertilizer should be banded. Its estimated that 50% of all the nitrogen a lettuce plants uses is taken up in the last weeks of growth so save a lot of nitrogen for late season banding as long as its not so late that the crop is damaged in the banding process. Be careful to not place bands too close to the lettuce plants as lettuce is very salt sensitive. Early season the lettuce plants may "sweat" nitrogen at the tips of the leaves - this is not a problem. Really late applications of nitrogen can at times not give a yield response.

Phosphorus

Use a soil sufficiency method to determine any needed phosphorus:

Mehlich test results ppm	Olsen Sodium Bicarbonate results ppm	Phosphate Requirement in Units./A P2O5
Above 70	Above 35	25 Units./A
50 - 70	26 - 32	40 Units./A
40 - 50	21 - 26	60 Units/A
30 - 40	15 - 21	80 Units/A
20 - 30	10 - 15	100 Units/A
10 - 20	5 - 10	125 Units/A

Phosphorus availability varies a lot in SLV soils. Adjustments should be made to these recommendations.

• Soils with pH's of above 8.4 add 20 Lbs./A to the above amounts.
• Soils with excess Calcium (excess lime) add 20 Lbs./A to the above amounts.
• On heavy soils add 20 Lbs./A

Potassium

Most western soils have sufficient potassium levels for a lettuce crops but some areas may need some additional potash applied. Use the following table to determine amounts needed:

K test value in ppm	less than 50	50-150	150-250	250-350	350-
K needed in Units./A	200	100	20	10	0

Sulfur

Lettuce is a medium - low user of sulfur which is a mobile nutrient like nitrogen which can move with soil water. Sulfur availability should be 1 unit of sulfur to 4 units nitrogen, but apply at least 30 units/A sulfur at a minimum.

Micro nutrients

Zinc

Zinc is the most common micro-nutrient problem in the San Luis valley of Colorado. Use the table below to calculate your zinc fertilizer needs:

Zinc test value in ppm	< 0.2	0.2 - 0.5	0.5 - 0.8	0.8 - 1.0	1.0 - 1.5	> 1.5
Zinc Needed in units/A	7	5	3	2	1	0.5

Apply the zinc with the pre-plant band or with a liquid nitrogen injection early in the season. Soils with high pH's and calcarious need higher zinc application amounts.

Other Micro Nutrients

Problems with other micro-nutrients are not common and related to specific local conditions. Often micro-nutrient problems are related to an imbalance of other nutrients. In this case, applying the micro-nutrient in shortage will not solve the problem, since the imbalance of other nutrients still exists.

Calcium

Calcium is a nutrient that is often short in a lettuce crop and can result in quality problems like internal tip burn. Calcium problems can occur even in soils high in calcium. Using calcium nitrate fertilizers can help a calcium problem, but not always. The problem may be related to that calcium uptake is difficult for the plant and at time of high growth rates the lettuce plant just can't uptake enough calcium for its use no matter how much is present in the soil. For other micro nutrients use these problem soil levels:

Nutrient	Level below which additional amounts may be needed:
Iron (Fe)	< 4.5 ppm
Manganese (Mn)	< 1.0 ppm
Copper (Cu)	< 0.2 ppm
Boron (B)	< 0.5 ppm
Magnesium (Mg)	< 50 ppm

Tissue testing can be very useful to see how a fertilizer program is really working. Although tissue testing results are usually not in time to change a crop in season, the results can be used to adjust future fertility programs. Sampling is easy, just collect wrapper leaves or fully expanded leaves from 12 heads in a representative area of the field. Put them in a labeled paper bag and store in a cool place and ship them to a lab for analysis as soon as possible. Below are some guidelines for interpreting the results. In many cases its important to refine guidelines for your area by regular sampling and sorting out results by good fields and bad fields and using the good fields' results as guidelines.

Note: This information should only be used as a guide. Adjustments for local conditions must always be made.

Return to Homepage