A Decade of Pepper Fertility Research

Regina P. Bracy  |  4/27/2006 2:30:59 AM

Regina P. Bracy

Bell peppers are grown extensively throughout southeastern Louisiana, with production concentrated in Tangipahoa and surrounding parishes. Gross farm value in 1999 was about $1.6 million.

Bell peppers are produced using transplants, supplemental irrigation and raised, fumigated beds covered with polyethylene mulch. Because of the intensive production, the cost of establishing and producing the crop is estimated at $3,700 per acre, even before harvesting begins.

Fertilizer costs have always been considered a small, insignificant part of the overall cost of vegetable production, but growers are realizing that small savings in fertilizer add up over acres and years. Also, the environmental impact that leaching of excess fertilizer has on surface and ground waters must be considered.

Researchers at the Hammond Research Station conduct field studies to develop the most efficient and effective use of fertilizer for bell pepper production. A discussion of the findings of a decade of pepper fertility research follows.

Phosphorus, potassium
Recommendations for phosphorus and potassium fertilization of bell pepper had been based on early work with mixed fertilizers. Improved cultivars, extensive management practices and different cultural systems required a re-evaluation of fertilizer recommendations.

Four rates (0, 100, 200, 300 pounds per acre) of phosphorus and potassium were applied to bell peppers in three experiments. Nitrogen rates of 100 pounds per acre preplant and 40 pounds per acre sidedressed were kept constant over all treatments.

Phosphorus had a greater effect on bell pepper production than potassium when soil levels of phosphorus and potassium were low. Rates of 200 pounds per acre of phosphorus and 100 pounds per acre of potassium are adequate for bell pepper production on soils low in phosphorus and potassium. Adding phosphorus and potassium fertilizer to soils with adequate levels (more than 100 milligrams) of phosphorus and potassium is not necessary for bell peppers grown with plastic mulch.

Nitrogen rates
Evaluations of various preplant nitrogen rates (from 0 to 200 pounds per acre) have indicated that at least 50 pounds per acre of nitrogen should be applied initially (preplant) under the mulch. Higher rates of initial nitrogen (100 to 200 pounds per acre) did not increase yields over the 50 to 80 pounds per acre rates, if the crop was sidedressed.

Fall or spring N
Because spring rains often prevent timely field operations, many growers prepare the field and apply preplant fertilizer and mulch in the fall for the spring bell pepper crop. Although mulch may offer some protection from Louisiana’s heavy rains, soluble fertilizer nutrients (particularly nitrogen) are still subject to leaching losses when applied in October for late March-early April planting.

Initial nitrogen rates of 0, 50, 100, 150 and 200 pounds per acre were applied in the fall and again in the spring to determine if initial fall fertilizer rates could be reduced. Phosphorus and potassium were banded in the bed center at the rate of 200 pounds per acre in October, and beds were covered with polyethylene mulch. Initial nitrogen treatments in the fallapplied treatments were banded with the phosphorus and potassium. The spring nitrogen treatments were injected through the mulch using a spoke-wheel injection system within one week of transplanting.

At higher rates of nitrogen, marketable and extra-large yields were not different for application timing. Applying the initial nitrogen fertilizer in the fall instead of the spring did not have an effect on production, if an initial nitrogen rate of more than 50 pounds per acre was used.

Using plastic mulch offers many benefits such as weed control and soil temperature modification. This method of production, however, hinders the application of fertilizer after the mulch has been applied. The common method of applying fertilizer after the mulch is in place is to drop the fertilizer in the furrow between beds or to punch holes through the mulch and manually place a small amount of fertilizer in the hole. A third method of applying fertilizer was introduced to the area several years ago and consists of injecting liquid fertilizer through the mulch with a spoke wheel.

Experiments were conducted to evaluate the effect of sidedress fertilizer applications on pepper yield and size. Plants were sidedressed twice after transplanting with nitrogen (40 pounds per acre) using one of three methods: (1) granular fertilizer mechanically dropped in the furrow between the beds, (2) granular fertilizer manually dropped between each plant in holes punched through the mulch and (3) granular fertilizer dissolved in water and injected through the mulch using a spoke wheel.

Yields of extra-large and marketable bell peppers were not affected (statistically) by the method of sidedress application, although there was a trend toward higher yields in plots sidedressed with the spoke-wheel injector. The use of the spoke-wheel injector increased yield at the first harvest, offering an advantage of producing more peppers during the early market when the price is usually most favorable.

Liquid fertilizer  
By injecting liquid fertilizer through the mulch, spokewheel injectors offer more accurate placement of plant nutrients, reduce leaching and potentially improve plant-uptake efficiency. If liquid fertilizer could be used to supply the preplant and sidedress fertilizer needs of the bell pepper crop, the practice of applying preplant granular fertilizer in the fall or spring would be eliminated. Applying mulch without preplant fertilizer would reduce fertilizer leaching and shorten the time needed for field preparation. Greater flexibility in timing of liquid fertilizer applications when the crop is growing could reduce overall fertilizer requirements, reduce potential losses through leaching and improve plant-uptake efficiency, since the fertilizer could be applied as needed.

Several studies were conducted to evaluate the effect of fertilizer type (granular or liquid), rate and timing on bell pepper production. Fertilizer treatments included a ½X, 1X and 2X rate of fertilizer applied at transplanting or split over two applications (at transplanting and two weeks after transplanting). Liquid fertilizer (10-10-10) was injected at the rates of 2340, 1170, 585 pounds per acre for the 2X, 1X and ½X rates, respectively. Granular fertilizer (13-13-13) at the rate of 900 and 450 pounds per acre for the 1X and ½X rates, respectively, was applied preplant in the fall.

Fertilizer type (granular or liquid) did not affect marketable yield or earliness, indicating that fertilizer application could be delayed until spring and a liquid formulation could be used. Splitting the fertilizer application, regardless of the rate applied, had a significant effect on size of bell pepper produced. Applying one-half the fertilizer two weeks after transplanting increased the yield of extra-large peppers.

Nitrogen sidedressing
Research at the Hammond Station has shown that bell peppers respond to additional applications of nitrogen fertilizer during the growing season. Sidedressing nitrogen has consistently increased total and extra-large yields, pepper weight and earliness in several different experiments. Applying additional nitrogen in sidedressing has had a more consistent effect on production than have preplant nitrogen rates. If sufficient initial nitrogen fertility (more than 50 pounds per acre) is provided, applying nitrogen fertilizer three to five weeks after transplanting has more effect on bell pepper size and production than either fertilizer rate, fertilizer type or fall/spring application timing.

What we learned
  • Bell peppers respond to sidedress nitrogen application.
  • Applying nitrogen fertilizer three to five weeks after transplanting had the most consistent and positive effect on production.
  • Nitrogen rate and initial fertilizer timing were not as critical for production when the initial nitrogen rate was at least 50 pounds per acre and the crop was sidedressed.
  • Rates of 200 pounds per acre of phosphorus and 100 pounds per acre of potassium are sufficient for production on most soil types.
  • Liquid fertilizer can be used for initial or sidedress application of fertilizer without affecting yield or fruit size.

(This article was published in the winter 2000 issue of Louisiana Agriculture.)

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