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Weekly UpdatesOBJECTIVE: The objective of this study was to evaluate spent mushroom substrate (SMS) at varying application rates and two different timings of application in a pumpkin crop.
MATERIALS & METHODS
The study was conducted in 2007 and 2008 on a one-acre field consisting of a Hagerstown silt loam and located at the Horticulture Research Farm, Russell E. Larson Research Center, Rock Springs, PA.
Treatments consisted of SMS applied assuming varying rates of mineralization and at two timings of application (Table 1). Additionally three control treatments were included: ammonium nitrate at a rate of 80 lbs nitrogen per acre applied at two timings and an unamended control. Based on compost analysis (Table 2) conducted by the Agricultural Analytical Services Laboratory, Penn State, the amount of material to apply was calculated. Treatments were arranged in a randomized complete block design. Lach treatment was replicated four times on plots 1125 [ft.sup.2] in size. Treatments implemented two or three weeks before planting were applied on May 15, 2007 and May 24-26, 2008 and soil incorporated on May 22, 2007 and May 26, 2008 to a depth of about eight inches using an S-tine. The remaining treatments were implemented on May 29, 2007 and June 12-13, 2008 and soil incorporated on the same day.
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Four-week-old Racer pumpkin plants were transplanted on May 30, 2007 and three-week-old plants were transplanted on June 16, 2008 using 3 ft in row spacing and 6 ft between rows. A drip irrigation system was installed to provide supplemental water to the plants when needed. Insect pests and diseases encountered included cucumber beetles, squash bugs, viruses and powdery mildew. These were managed with insecticide and fungicide sprays. Weeds were managed by periodic cultivation.
Soil samples were collected from each plot on May 21, 2007 and May 23, 2008 prior to applying treatments and on Sept. 29, 2007 and Sept. 26, 2008 after harvest. Samples were collected with a soil auger to a depth of 12 inches. Samples were submitted to the Agricultural Analytical Services Laboratory, Penn State for analysis of soil properties and nutrient levels.
Leaf samples for nutrient analysis were collected on July 11, 2007 and July 28; 42 days after planting, night recently fully expanded mature whole leaves (petioles were removed) were harvested from border plants in each plot. Leaf samples were submitted to the Agricultural Analytical Services Laboratory, Penn State for determination of micro and micro-nutrient contents.
Hand harvest occurred on Sept. 20, 2007 and Sept. 15, 2008. Yield parameters measured and recorded were the weight and number of marketable and unmarketable pumpkins. Unmarketable pumpkins were categorized as diseased, damaged by insects or under mature (less than 50 percent orange).
Data were analyzed with General Linear Model Analysis of Variance using Statistical Analysis System 9.1.3. When significant differences at P [less than or equal to] 0.05 were detected, Duncan's least significance difference test was used to separate means.
RESULTS & DISCUSSION
Total Yield
In both years, the lowest yields by weight were observed when no supplemental nutrients were supplied (Tables 3 and 4). This was expected as nutrients are applied to maximize yield potential.
In 2007, larger yields by weight were observed from plants where SMS was applied at planting assuming a 10 percent mineralization rate compared to applying SMS two weeks before planting using a 10 percent mineralization rate or applying inorganic fertilizer. Intermediate yields resulted from applying SMS with a 20 percent mineralization rate regardless of timing of application. Applying SMS using a 10 or 20 percent mineralization rate and applying at planting resulted in a higher number of pumpkins produced than applying ammonium nitrate two weeks before planting to supply nutrients or providing no supplemental nutrients. All other treatments resulted in intermediate numbers of pumpkins being produced.
In 2008, larger yields by weight were observed from plants where SMS was applied at planting assuming a 10 percent mineralization rate compared to applying SMS assuming a 20 percent mineralization rate and ammonium nitrate at planting. Applying SMS assuming a 20 percent mineralization rate and ammonium nitrate three weeks prior to planting resulted in intermediate yields by weight. In terms of numbers of pumpkins produced, applying ammonium nitrate three weeks before planting resulted in the most pumpkins. All other treatments resulted in more pumpkins being produced than supplying no supplemental nutrients, but not different from each other.
In both years of the study, applying SMS at planting assuming a 10 percent mineralization rate resulted in large yields by weight. Nitrogen availability based on this treatment was likely higher than the other SMS treatments, the nitrogen in compost is primarily in two forms: the organic form and ammonium-N. The pumpkin plants likely benefited from the application of both nitrogen sources as well as other compost properties. Ammonium is readily available for plant use while organic nitrogen must be mineralized prior to becoming available for plant uptake. In 2007 the SMS contained 1.4 lbs ammonium per ton. Using a 10 percent mineralization rate to apply the SMS resulted in 37 lbs of ammonium/acre; 20 percent mineralization rate resulted in 24 lbs ammonium/acre; and 40 percent mineralization rate resulted in 14 lbs of ammonium/acre. In 2008 the SMS contained 1.2 lbs ammonium per ton. Using a 10 percent mineralization rate to apply the SMS resulted in 32 lbs of ammonium/acre; 20 percent mineralization rate resulted in 20 lbs ammonium/acre; and 40 percent mineralization rate resulted in 11 lbs of ammonium/acre. Timing was also a factor with SMS application at planting resulting in the largest yields. Ammonium is a cation and subject to volatilization while nitrate is subject to leaching. It is possible that applying two or three weeks earlier resulted in some ammonium volatilization and nitrate leaching before planting.
Marketable & Unmarketable Yield
In 2007, the number of marketable pumpkins produced was not different by treatment (Table 3). Applying SMS using a 10 percent mineralization rate and applying at planting resulted in the largest yield by weight.
In 2007, the fewest number and lowest total weight of culls resulted from no supplemental nutrient application (Table 3). Unmarketable pumpkins were further categorized as diseased, damaged by insects or under mature. Pumpkins categorized as diseased often also exhibited insect damage. The number and weight of diseased and under mature pumpkins were not different by treatment (Table 5). In general, the unamended treatment resulted in the least insect damaged pumpkins by number and weight.
The 2007 growing season was hot and dry. Water was supplied to the plants via a drip irrigation system between rain events when needed. However, across the state pumpkin maturity was hastened due to these environmental conditions. To have pumpkins during the peak of the selling season (around Halloween for face pumpkins), it was recommended that growers either harvest and store their pumpkins in cool dry conditions or delay harvest and spray fungicides to minimize rot. In this study fungicides were sprayed in the field to minimize diseases and harvest was delayed. Despite these efforts a considerable amount of pumpkins rotted and the ideal time for harvesting was slightly missed. For these reasons, marketable yield was somewhat low and unmarketable yield was somewhat high.
In 2008, marketable yields by weight were higher from plants where SMS was applied at planting assuming a 10 percent mineralization rate than when SMS was applied three weeks prior to planting assuming a 20 percent mineralization rate and not applying supplemental nutrients (Table 3). All other treatments resulted in intermediate marketable yields by weight. More marketable pumpkins were the result of applying ammonium nitrate at planting than applying SMS assuming a 20 percent mineralization rate regardless of timing, assuming a 10 percent mineralization and applying it three weeks prior to planting or using no supplemental nutrients.
In 2008, very few pumpkins were unmarketable and no significant differences between treatments were detected (Table 3). No differences were detected when unmarketable pumpkins were sorted by insect damage, disease or immaturity (data not shown).
Just as with total yield, in both years of the study applying SMS at planting assuming a 10 percent mineralization rate resulted in large marketable yields by weight. In 2008, most other treatments resulted in marketable yields not different than when applying SMS at planting and assuming a 10 percent mineralization rate. Based on these results, this treatment would most likely result in successful pumpkin production when using these methods.
Pre-Season Soil Properties
To serve as baseline levels, the soil properties of each plot were analyzed. In 2007, soil pH and phosphate, potash, magnesium and calcium levels were not different prior to implementing treatments (Table 6). These levels exceeded crop needs for calcium (using Penn State recommendations). They were within optimal ranges for the other nutrients (about 330-480 lbs/acre for Mg; 275-710 lbs/acre for phosphate; 225-400 lbs/acre for potash). In 2008, phosphate, potash, magnesium and calcium levels were not different across the field and once again exceeded crop needs (Table 7). Also, soil pH levels varied slightly throughout the field.
Post-Season Soil Properties
In 2007 using a 10 percent mineralization rate to apply SMS resulted in higher phosphate levels than using a 40 percent mineralization rate, applying ammonium nitrate or not applying supplemental nutrients (Table 8). Using a 20 percent mineralization rate to apply SMS resulted in intermediate soil phosphate levels at the end of the growing season.
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