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Wilton P. Cook and Douglas C. Sanders

Studies were conducted to determine the effect of N application frequency through drip irrigation on soil NO3-N movement in the bed profile and on yield and N uptake by tomato plants (Lycopersicon esculentum Mill. `Sunny') at two locations. Increasing N application frequency resulted in increased yields at Clayton, N. C., but not at Charleston, S.C. The number of fruit produced was not affected by N treatment at either location, but fruit size increased with increasing N application frequency at Clayton. Foliage N concentration decreased seasonally, but neither foliage N concentration nor total N content of the above-ground portion of the plants was affected by N application frequency. Regardless of N application frequency, NO3-N concentrations within the raised bed decreased with time due to plant uptake and leaching. Nitrogen levels declined most rapidly in the area closest to the drip tube.

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Jason M. Lilley and Elsa S. Sánchez

technique (2012). The remainder of the nutrient needs was supplied by broadcasting 5N–0.4P–0.8K granular fertilizer (Blue N; Fertrell Co., Bainbridge, PA) before field preparation. Soil nitrate levels Presidedress nitrate (NO 3 -N) tests were conducted

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Juan Carlos Gilsanz, D. C. Sanders, and G. D. Hoyt

Rye plus crimson clover cover crops were followed by spring potato and fall snap bean or sorghum or fallow. The soil samples at 15 cm increments to 90 cm were evaluated for nitrate levels after each crop and cover crop. After the cover crops, soil nitrate levels were reduced relative to the fallow area. After the potato, crop soil nitrate levels increased above initial spring levels due a uniform fertilization due to the amount of N applied and short cycle of the crop. Snap beans and sorghum had increased plant stands and reduced soil impedance after fall cover crops. HOW nitrate levels varied with soil depth and time will be discussed.

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H.H. Krusekopf, J.P. Mitchell, T.K. Hartz, D.M. May, E.M. Miyao, and M.D. Cahn

Overuse of chemical N fertilizers has been linked to nitrate contamination of both surface and ground water. Excessive fertilizer use is also an economic loss to the farmer. Typical N application rates for processing tomato production in California's Central Valley are 150-250 kg·ha-1, and growers generally fail to fully consider the field-specific effects of residual soil NO3-N concentration, or N mineralization potential of the soil. The purpose of this research was to determine the effects of sidedress N fertilizer application, residual soil NO3-N, and in-season N mineralization, on processing tomato yield. Research was conducted during the 1998 and 1999 growing seasons at 16 field sites. Pre-sidedress soil nitrate concentration was determined at each trial site to a depth of 1 m, and aerobic incubation tests were conducted on these soils (top 0.3 m depth) to estimate N mineralization rate. Sidedress fertilizer was applied at six incremental rates from 0 to 280 kg N/ha, with six replications of each treatment per field. Only five fields showed yield response to fertilizer application; yield response to fertilizer was associated with lower pre-sidedress soil nitrate levels. In most fields with fertilizer response, yield was not increased with sidedress N application above 56 kg·ha-1. Mineralization was estimated to contribute an average of ≈60 kg N/ha between sidedressing and harvest. These results suggest that N fertilizer inputs could be reduced substantially below current industry norms without lowering yields, especially in fields with higher residual soil nitrate levels.

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B.D. McGraw and B. Bostian

In March 1992 treatments were established in a split plot design to compare vegetable yield and nutrient buildup effects of 94 kg of 34-0-0, 1345 and 2692 kg/ha spent poultry litter under fallow or wheat rotation cover. The 2692 kg litter treatment caused a nonsignificant decrease in `Crimson Sweet' watermelon yield. Wheat was planted on half the plot area in September 1992 and harvested in March 1993. Fertilizer and litter treatments were reapplied in April and `Merit' sweet corn was planted. Corn plant growth was more vigorous and yield was significantly higher in fallow plots irrespective of litter treatment. Sweet corn yield was highest in plots treated with 2692 kg liter/ha. NO3, K, SO4, and Mg content of the top 30 cm of soil was decreased by wheat. Soil nitrate level remained below the pretreatment level after the first year except for the 2692 kg litter/fallow treatment. Soil P at the 0-30 cm depth remained the same as or higher than the initial level in all treatments. Soil K content exceeded initial test levels in all fallow treatments and one wheat treatment.

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K.M. Batal

Various applications of N fertilizer formulations to bell pepper plots were made to affect soil nitrate-N concentrations from 5 to 30 ppm throughout the growing season. Number and weight of marketable grades for the 1st and 3rd harvests were improved by increasing soil N from 5 to 30 ppm. In the final (4th) harvest, marketable yield was highest for applications maintaining soil N of 25 ppm. Earliness was enhanced by N sources with Ca(NO3)2 producing the earliest yield followed by NaNO3 and NH4NO3. Total marketable yield produced by Ca(NO3)2 or NaKNO3 was 3 t/ha higher than by NH4NO3 applications. High marketable quality was maintained with Ca(NO3)2 and NaNO3 treatments. The highest blossom-end rot (BER) incidence was associated with NH4NO3 applications. But the N source effect on BER was strongly influenced by soil nitrate levels. At 10-20 ppm soil N, leaf Ca decreased during the 8 to 12 week period, but at higher soil N, leaf Ca remained unchanged, indicating a constant Ca uptake during the critical growth period.

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Francis X. Mangan, John Howell, and Stephen Herbert

Hot cherry peppers were grown after incorporation of the following three winter cover crop regimes in Summer 1994—hairy vetch (Vicia villosa) plus winter rye (Secale cereale), hairy vetch alone, and no cover crop. For each main effect there were three N rates applied to peppers in three applications over the course of the season: 0, 85, and 170 kg·ha–1. The pepper yield was significantly higher with hairy vetch plus rye than rye alone or no cover crop. There was also no significant yield increase with the addition of N fertilizer to the peppers grown with hairy vetch. Soil nitrate–N levels taken just prior to N sidedress were significantly higher in plots that had hairy vetch plus rye compared to other treatments. There was also a significant linear relationship of the soil nitrate–N levels among the three N rates. Based on the results of this study, sidedressing peppers would be recommended when soil nitrate levels are above the 25 ppm that is the current threshold for other crops. SPAD readings were taken several times during the season. There was a high correlation of SPAD readings to pepper yield very early and very late in the season. The correlation of SPAD readings to pepper yield was poorest when taken at the time of N sidedress.

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Suzanne E. Allaire, Jean Caron, Isabelle Duchesne, Léon-Étienne Parent, and Jacques-André Rioux

A 2-year experiment with Prunus ×cistena sp. was conducted in pots using seven substrates composed of various proportions of primarily peat, compost and bark. Peat substrates significantly affected root and shoot dry weight. Water desorption characteristics and saturated hydraulic conductivity were measured in situ to estimate the pore tortuosity factor and the relative gas diffusion coefficient. The pH, electrical conductivity, C/N ratio, total and hydrolyzable N, as well as NO3 --N and NH4 +-N in solution were also measured. Estimates of the physical properties suggest that a lack of aeration limited plant growth. Plant growth was significantly correlated with both the gas relative diffusivity and the pore tortuosity factor. Among the chemical factors, pH and soil nitrate level were also correlated with plant growth. No significant correlation was found between plant growth and air-filled porosity or any other measured chemical properties. This study indicates that an index of gas-exchange dynamics could be a useful complementary diagnostic tool to guide substrate manufacturing.

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Meghan A. Curless and Keith A. Kelling

Within Wisconsin, there is a distinct movement toward dairy herd expansion and consolidation of small farms. These large dairies are considering various land and manure management arrangements with non-livestock farmers, such as potato (Solanum tuberosum) producers to increase their manure management options. This study used a fertilizer equivalence approach to evaluate the availability of nitrogen from dairy manure to potatoes. Nitrogen (N) availability was evaluated in field experiments in 2000 and 2001, conducted in northeast Wisconsin using a moderate and a high liquid dairy manure rate [10,000 and 20,000 gal/acre (93,536 and 187,072 L·ha-1)] compared with results obtained from N fertilizer applied at five rates [0 to 240 lb/acre (269.0 kg·ha-1)]. Availability estimates using the fertilizer equivalence method based on tuber yield, harvested tuber N concentration and uptake, petiole nitrate concentration, and soil nitrate levels resulted in apparent availability of manurial N from 10% to 40%, with an overall average across both years of 29.2%. This level is only slightly less than values typically measured where corn has been used as the test crop. In spite of being more shallow-rooted and perhaps somewhat less efficient in N use it does not appear that adjustments to manurial N availability estimates are warranted when potatoes are grown.

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Juan Carlos Díaz-Pérez and Touria E. Eaton

Eggplant (Solanum melongena L.) is an increasingly popular crop in the United States. In the southeastern United States, eggplant is often produced with high levels of irrigation water [above the rate of crop evapotranspiration (ETc)], resulting in water waste and nitrogen (N) leaching. The objective of this research was to assess the effects of irrigation rate on plant growth and fruit yield in eggplant. The study was conducted in Tifton, GA, in the fall of 2010 and 2011. Eggplant plants cv. Santana were grown on raised beds (1.8 m centers) covered with white plastic film mulch. There was a single drip tape along the center of the bed. The design was a randomized complete block with five treatments and four replications. Treatments consisted of irrigation rates based on ETc (33%, 67%, 100%, 133%, and 167% ETc). Plant growth, chlorophyll index (CI), and volumetric soil water content (SWC) were monitored over the season. In 2010, SWC (0–30 cm deep) increased and soil nitrate levels decreased with increasing irrigation rates. Foliar N and potassium (K), and CI decreased with increasing irrigation rate, probably due to a dilution effect. Stem diameter, leaf dry weight (DW), and vegetative top DW increased with increasing irrigation rate. Net photosynthesis and stomatal conductance (g S) were lowest at 33% ETc. Fruit number and fruit yields (marketable and total) were also lowest at 33% ETc and there were little yield differences among irrigation rates higher than 33% ETc. In 2011, irrigation rate had minor or no effect on SWC, plant growth of mature plants, leaf gas exchange, and fruit number and yield. The no treatment effect observed for eggplant in 2011 was likely because study was conducted in a low field that remained moist most of the time, nullifying the treatment effects. Results suggested that eggplant may tolerate mild water stress, since plants irrigated at 67% ETc produced fruit yields similar to those of plants irrigated at 100% ETc or higher rates. Thus, there is a potential to save water by reducing current irrigation rates without negatively impacting fruit yields.