Masters Theses

Date of Award

12-1992

Degree Type

Thesis

Degree Name

Master of Science

Major

Plant, Soil and Environmental Sciences

Major Professor

David L. Coffey

Committee Members

James Wyatt, Donald Howard

Abstract

Evaluation of fertilizer rates, nutrient sources, time and method of application has been one of the major research areas to improve growth, development and yield of cowpeas. The first year of research consisted of three experiments evaluating, 1.) the effects of nitrogen (N) rates, N sources, time of N application, 2.) foliar N applications, and 3.) Phosphorus (P) and potassium (K) fertilization rate of southern peas. In the second year the experiments were expanded to include tests on cowpea responses to ratooning and starter fertilizer nutrient combinations.

Research was established on a Collins silt loam (Aquic Udifluvent, coarse-silty, mixed, acid, thermic) at the West Tennessee Experiment Station, Jackson, Tennessee. In 1990, the site was fall planted in wheat which was cut and removed prior to planting. The experimental designs varied with each experiment.

Some of the N applied in 1990 may have been immobilized by the decomposing wheat roots. This immobilization may have resulted in less N being available for uptake during the growing season requiring higher application rates for a response. In 1991, cool temperatures and excessive rains after planting may have resulted in cowpea yields being considerably lower than the 1990 yields. During the months of May and June, precipitation was 10.32 and 6.17 inches, respectively, with an average temperature of 83° F.

The yield of cowpeas were not significantly affected by N source, N rate, or time of application. Yields varied slightly as a result of N source. Splitting the rate of applied N did not affect yields. Leaf N concentration was also unaffected by N rate, N source, and time of application. Both yields and leaf N concentrations varied due to year. Leaf N concentrations for the 60 lb/a rate was 2.83 percent N in 1990 compared to 4.24 percent in 1991. The highest mean yield was produced by the 30 lb/A N rate. Yields tended to be reduced with the 90 lb/A N rate.

In another test, cowpea yields were increased from soil applied and foliar applied N. In 1990, yields were increased with N rates up to 60 lb/A soil applied and 20 lb/A foliar applied. In 1991, yields were increased by soil applying 30 lb/A and foliar applying 10 lb/A of N.

Phosphorus and K fertilizer applications had no significant affect on cowpea yields when analyzed by year. Yields averaged across years showed that applying 120 lb/A of P2O5 reduced yields when compared with the 60 lb/A rate. Yields were unaffected by broadcasting K2O. Phosphorus and K application rates had no significant effect on P, K, Ca, or Mg leaf concentrations. Applying 90 or 120 lb/A of P2O5 increased soil test levels from medium to high.

Cowpea yields for both the main crop and the ratoon crop were not affected by fertilizer treatments applied at planting. The main crop was planted on May 23 and harvested on August 5 for a total of 73 days from planting to harvest. The ratoon crop was harvested on September 27, 53 days after harvesting the main crop. The time interval between harvesting the main and ratoon crop was reduced 20 days for the ratooned crop. The ratooning process added an average of 1030 lb/A of shelled peas or an increase of 77 percent to the total yield.

Starter fertilizer treatments had no effect on yields. Yields ranged from 1077 to 1200 lb/A, with no marked differences between broadcast or the band (starter) treatment.

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