- Researchers Use New Approaches to Pumpkins in the South
- By Dr. Joe Kemble and Daniel Carroll
Auburn University
- The commercial pumpkin production industry in Alabama has increased over the past 10 years from approximately 200 to almost 1,200 acres. Most of this acreage is direct-seeded (end of June to mid July), bare ground production without the benefit of supplemental irrigation.
The most critical limiting factor for pumpkin production in Alabama is adequate soil moisture. Despite being regarded as a drought-tolerant crop, pumpkins do benefit from timely irrigation especially during stand establishment and sizing of fruit. Deficiencies in soil moisture lead to reduced stands, reduced yields, reduced fruit size and reduced fruit quality.
The use of cover crops and conservation tillage (no-till, strip-till) is not a new concept especially in row crops such as cotton and corn. In those crops, certain cover crops and conservation tillage systems have enhanced soil moisture retention and aided in weed suppression. The use of legume cover crops can help reduce the need for the application of supplemental nitrogen.
Four-year study
We conducted a four-year study (1999-2002) in Alabama aimed as developing a more sustainable pumpkin production system using legume cover crops and strip tillage.
Strip-tillage is a form of conservation tillage in which a portion of the soil surface is tilled and subsoiled, usually the in-row portion, and the row middles are maintained undisturbed with residues. The strip-tillage implement was composed of a front cutting culter, two fluted culters directly behind it, a plow to rip open a furrow, followed by a rolling basket.
In this study we compared three cover crop treatments – hairy vetch, yuchi arrowleaf clover, and a mixture of winter wheat plus crimson clover. The performance of these covers was compared to a bare ground treatment that represented typical conventional production in Alabama. Each cover crop was sown by mid to late October preceding the following summer’s pumpkins. The vetch and yuchi were sown at a rate of 40 pounds per acre and the wheat/crimson cover was sown at a rate of 100 pounds per acre and 40 pounds per acre, respectively.
In addition, we also examined the effect of varying rates of nitrogen (0, 45 and 90 pounds per acre nitrogen) within each of the cover crops and the bare ground treatment.
The cover crops were allowed to grow and mature until two to three weeks before seeding time for the pumpkins. Biomass samples were taken at peak maturity for each cover crop to determine how much biomass each produced and to calculate carbon to nitrogen (C:N) ratios. In most years, the cover crops had died back sufficiently to allow rolling and subsequent strip tillage. When needed, paraquat or glyphosate was applied one to two weeks prior to tillage. Based on soil test results, all lime, phosphorous, potassium and other nutrients were applied prior to planting of pumpkins. Nitrogen was applied pre-plant to all treatments except the zero-pound-per-acre nitrogen treatments. Additional nitrogen was applied to the appropriate treatments.
Throughout the season, we measured soil moisture levels at varying depths both between the rows and within the plant rows, evaluated the nutritional status of the pumpkins, monitored weed pressure, and at harvest, we determined the total number of fruit and yield.
What we found
C:N ratios are important because the higher the ratio is (above 27:1), the more nitrogen will be tied up. The lower the ratio, more nitrogen will be released into the soil for immediate use. The ideal range is between 15:1 and 25:1. An estimated 40% of nitrogen from decomposing plant tissue becomes available the first year. In the four years of this research, C:N ratios for vetch averaged 12:1, for yuchi 17:1, and for wheat plus crimson clover 23:1.
The cover crops effected yield, average fruit weight, and average fruit number. In each year, yields were highest (ranging from 10 to 12.5 tons per acre) for the hairy vetch and yuchi arrowleaf clover treatments regardless of the nitrogen rate that was applied. The bare ground treatments averaged approximately 7.5 tons per acre. Average fruit weight was also higher in all of the cover crop treatments, averaging 12.5 pounds of fruit for each of the cover crops and 10 pounds of fruit for the bare ground treatment. The number of fruit per acre averaged 1,850 for the cover crop treatments and 1,500 for the bare ground treatment.
Over the four years of this study, nitrogen rate did not interact with any of the cover crop treatments. This means that the effect of nitrogen rate was the same regardless of the nitrogen rate. A better way to think about this is to say that the trend was the same. As nitrogen rate increased, yield, average fruit weight, and average fruit number increased despite the cover crop. What is interesting to note is that there were significant differences between the zero pound per acre N rate and the 45-pound-per-acre and 90-pound-per-acre nitrogen rate for yield, average fruit weight and yield. There were no differences, however, between the 45-pound-per-acre nitrogen rate and the 90-pound-per-acre nitrogen rate. This indicated that you did not receive any benefit (in terms of yield, fruit size, or fruit number) by applying more than 45 pounds per acre of nitrogen even on the bare ground plots.
In terms of soil moisture, the yuchi arrowleaf clover, hairy vetch, and wheat plus crimson clover residues helped to maintain higher soil moisture levels in between the rows of pumpkins. There were no differences within the rows due to the use of drip irrigation. In all cases, the bare ground treatments maintained the lowest soil moisture. Nitrogen rates within any of the cover crops did not affect soil moisture.
Weed pressure was the lowest in the wheat plus crimson clover treatment as compared to the other cover crops. Both yuchi arrowleaf clover and hairy vetch did not perform as well but performed better in suppressing weed growth compared to the bare ground treatment.
Take home message
The use of legume cover crops enhanced the growth and development of pumpkins – yield, average fruit weight and average fruit number per acre - all increased as compared to the conventional bare ground production.
Cover crops reduced weed pressure and helped to mediate soil moisture levels between the rows providing a reservoir of moisture for the pumpkins.
In Alabama, growers can safely reduce by one-half the nitrogen rate (45 pounds per acre instead of 90 pounds per acre) on pumpkins without a detrimental effect to yield or quality whether they are using a cover crop or producing on bare ground.
In any case, it is never a good idea to jump full bore into altering your entire operation to use the system we have outlined. Growers should evaluate their current production methods, environment, management style, etc. to determine if this will fit into your overall farm plan. Try it on a limited scale the first year then scale up.
