were maximized at 93 and 78 Mg⋅ha −1 , respectively, by a plant population of 385,000 plants⋅ha −1 in the Treasure Valley. In the mid-1990s, Treasure Valley packers started marketing a new onion bulb size class (super colossals, bulb diameter >108 mm
Clinton C. Shock, Erik B.G. Feibert, Alicia Riveira and Lamont D. Saunders
George E. Boyhan, Reid L. Torrance, Jeff Cook, Cliff Riner and C. Randell Hill
greater overall yields, but smaller bulbs. Finally, soluble solids and bolting (flowering) were not significantly affected. In a similar study, increasing plant population increased yield on clay or sandy soils ( Abo-Zeid and Farghali, 1996 ). In addition
Kent E. Cushman, Thomas E. Horgan, David H. Nagel and Patrick D. Gerard
Pumpkins (Cucurbita pepo, C. moshata) were grown in northern Mississippi during 2000 and 2001 for the purpose of more narrowly defining plant population recommendations for commercial production in the humid southeastern United States. Four plant populations were examined for `Aspen': 908, 1361, 2045, and 3068 plants/acre (2244, 3363, 5053, and 7581 plants/ha, respectively) and for `Howden Biggie': 605, 908, 1361, and 2045 plants/acre (1495, 2244, 3363, 5053 plants/ha, respectively). Plant populations were adjusted by varying in-row spacing while holding between-row spacing constant at 8 ft (2.4 m). Plant population significantly affected yield of `Aspen' and `Howden Biggie'. Linear and quadratic terms were significant for `Aspen', with maximum yield (ton/acre and fruit/acre) for the quadratic relationship occurring at about 2045 plants/acre. In contrast, yield of `Howden Biggie' decreased significantly (ton/acre) and nonsignificantly (fruit/acre) in a linear relationship as plant population increased from 605 to 2045 plants/acre. Plant population significantly affected fruit weight and size. As plant population increased, weight and size decreased slightly but significantly in a linear relationship for `Aspen' (lb/fruit and inch3/fruit) and `Howden Biggie' (lb/fruit). The quadratic relationship for `Howden Biggie' (inch3/fruit) was significant and the minimum value occurred at about 1361 plants/acre. Plant population significantly affected pumpkin yield components associated with plant productivity. As plant population increased, number and weight of fruit per plant decreased sharply in a quadratic relationship for `Aspen' (lb/ plant and fruit/plant) and `Howden Biggie' (lb/plant). The linear relationship for `Howden Biggie' (fruit/ plant) also decreased significantly. At the highest plant populations for `Howden Biggie', 40% of the plants did not produce marketable pumpkins. In conclusion, recommendations of optimum plant populations for a semi-vining cultivar such as `Aspen' should be centered on about 2045 plants/acre. Published recommendations from Kentucky appear sound, advocating plant populations within the range of 1360 to 2720 plants/acre (3361 to 6721 plants/ha). For a vining cultivar such as `Howden Biggie', recommendations can be as low as 605 plants/acre. Published recommendations from Kentucky and Georgia, along with those published in the Vegetable Crop Guidelines for the Southeastern U.S., advocate plant populations for vining cultivars of approximately 725 to 1465 plants/acre (1790–3620 plants/ha). Our results with `Howden Biggie', a cultivar that produces larger pumpkins than most other vining cultivars grown for the wholesale market, indicate that producers of vining cultivars should use plant populations from the lowest values of these recommendations or use even lower values. Our results also indicate that growers can control size and weight of pumpkins by varying plant population, with increasing populations resulting in a slight decrease of size and weight.
Peter J. Stoffella and Mike F. Fleming
Cabbage [Brassica oleracea L. (Capitata Group) cv. Bravo] transplants were grown on raised beds at Fort Pierce, Fla., during Fall 1987 and 1988. Plants were spaced at 8, 15, 23, 30, and 38 cm within rows or populations equivalent to 123,000, 61,500, 41,000, 30,800, and 24,600 plants/ha. Individual root weights, total plant weights, and core length increased linearly as within-row spacing (WRS) increased in both experiments. Untrimmed head weights, trimmed head weights, head height, head width, and core width increased quadratically as WRS increased in both experiments. Head shape and core index did not differ among WRS in either experiment, except for a quadratic increase in the head height: bead width ratio (head shape) as WRS increased in the 1988 experiment. Coefficients of variability (cv) for most measured variables decreased as WRS increased, indicating a reduction in plant-to-plant variation. Optimum marketable cabbage head size (>1 kg) and lower plant-to-plant variation (cv < 20%) were obtained at WRS of 23 cm or wider. However, trimmed cabbage yields decreased linearly as WRS increased in both experiments. In this study, a lower plant population (WRS > 23 cm) was more conducive to a once-over cabbage harvest since plant-to-plant variation in head size and other yield and quality characteristics was reduced.
Clinton C. Shock, Erik B. G. Feibert and Lamont D. Saunders
Onion (Allium cepa L.) production in the Treasure Valley of eastern Oregon and southwestern Idaho has been based on furrow irrigation with 318 kg·ha-1 N fertilizer and average yields of 70 Mg·ha-1, but these practices have been implicated in nitrate contamination of groundwater. Drip irrigation, introduced in the early 1990s, has several advantages, including reduced leaching losses. Since onion plant populations and N fertilizer rates can affect economic returns, studies were conducted in 1999, 2000, and 2001 to determine optimum plant populations and N fertilizer rates for subsurface drip-irrigated onion. Long-day onion (`Vision') was subjected to a combination of seven nitrogen fertilization rates (0 to 336 kg·ha-1 in 56-kg increments applied between late May and early July) and four plant populations (185, 250, 300, and 370 thousand plants/ha). Onion was grown on silt loam in two double rows spaced 0.56 m apart on 1.1 m beds with a drip tape buried 13 cm deep in the bed center. Soil water potential was maintained nearly constant at -20 kPa by automated irrigations based on soil water potential measurements at a 0.2-m depth. Onion bulbs were evaluated for yield and grade after 70 days of storage. Onion yield and grade were highly responsive to plant population. Onion marketable yield increased, and bulb diameter decreased with increasing plant population. Within the range of plant populations tested, gross returns were not always responsive to plant population. Returns were increased by the increase in marketable yield obtained with higher plant population, but higher plant population also reduced the production of the largest sized bulbs which had the highest value per weight. Onion yielded 95 Mg·ha-1 with no applied N fertilizer, averaged over plant populations and years. Onion yield and grade were not responsive to N fertilizer rate or interaction of N fertilizer rate with plant population. Preplant soil available N, N mineralization, and N in irrigation water all contributed N to the crop. Onion N uptake did not increase with increasing N fertilizer rate.
Elsa Sánchez, Kathleen Kelley and Lynn Butler
Eight edamame (Glycine max) cultivars were evaluated in the field in 2002, 2003, and 2004 to determine suitability for growing in central Pennsylvania. Data collection included plant populations (percent stand), marketable and unmarketable yields and edamame pod and bean quality indicators. Plant populations varied by year and cultivar and were generally below 80%. The effect of temperature on seedling emergence, and therefore plant populations, was evaluated for four edamame cultivars by using growth chambers programmed with varying day/night temperature regimes. Seedling emergence varied by cultivar and was generally below 80% with two exceptions. When grown in a 70/60 °F day/night temperature regime, `Butterbeans', and `Early Hakucho' exceeded 80% seedling emergence. In the field trial, plant populations affected marketable yields. Pod and bean quality were dependent on cultivar. Results indicated that `Butterbeans', `Early Hakucho', `Green Legend', `Shironomai', `Butterbaby', and `Lucky Lion' appear promising for growing in Pennsylvania based on pod and bean quality. However, the issue of poor seedling emergence and plant populations presents a major constraint to commercial production and needs to be studied further.
Stephen Reiners and Dale I.M. Riggs
Field studies were conducted in 1996 on two pumpkin (Cucurbita pepo L.) cultivars, `Howden' (vining-type growth habit) and `Wizard' (semi-bush growth habit), at two locations to determine the effect of plant population and row width on marketable yield. Increasing plant populations from 2990 to 8960 plants per hectare resulted in significantly greater fruit number and yield at both locations and for both varieties. Average fruit size declined at the highest populations. Increasing row width from 1.8 to 3.6 m resulted in a slight but significant decrease in number of fruit per hectare with no effect on other yield parameters. At one location, the effect of row width on yield and number of fruit per hectare depended on the population. At low populations, row width did not influence yield or fruit number; at high populations, wide rows produced lower yield and fewer fruit than narrow rows. The results demonstrate that growers may increase pumpkin yield by increasing plant populations but should use narrower row widths and wider in-row spacing. Growers who choose higher populations should ensure that all inputs are optimized to reduce potential plant-to-plant competition and use regionally adapted cultivars.
Charles A. Powell, Peter J. Stoffella and Harry S. Paris
Zucchini squash (Cucurbita pepo L.) fruit yield and the incidence of sweetpotato whitefly (SPWF) [Bemisia tabaci (Gennadius)], squash silver leaf (SSL) disorder, and zucchini yellow mosaic virus (ZYMV) were measured during Spring and Fall 1991 in experiments containing various plant populations. In both experiments, as the within-row spacing increased from 30.5 to 76.2 cm or the number of plants per hill decreased from three to one, the number of marketable fruit per hectare decreased, and the marketable fruit per plant increased. Adult SPWF populations increased with decreased within-row spacing in the spring but not the fall experiment. The incidence of SSL or ZYMV infection was not affected by plant population in either experiment. The results indicate that increasing zucchini squash plant population can increase yield without affecting the incidence of SSL or ZYMV.
Anusuya Rangarajan, Betsy A. Ingall, Michael D. Orzolek and Lewis Otjen
Butternut squash (Cucurbita moschata) plants are susceptible to defoliation and plant population (stand) reduction by insect, disease, temperature extremes, water, hail, or other mechanical damage. The timing of such losses may have variable effects on final fruit quality and yield. The objectives of these studies were 1) to determine the influence of the degree and timing of defoliation and stand reduction on the marketable yield of winter squash; 2) to determine yield compensation after stand reduction and defoliation; and 3) to explore effects of defoliation on fruit total carotenoid content. Experiments were conducted over 2 years in New York and Pennsylvania to explore these objectives. Marketable yields consistently improved with increasing plant population. If population losses occurred while plants were in the rapid vegetative growth phase, the remaining plants responded by increasing fruit number and weight per plant. Plant losses later in the season during fruit enlargement, however, did not elicit the same magnitude of response. Defoliation of 66% leaf area reduced marketable yields, and effects were most severe under high plant populations. Competition among plants restricted compensation. Moderate defoliation (33%) reduced yield in only one of three studies. This level of defoliation also increased the percentage of medium [1.0 to 1.5 kg (2.20 to 3.31 lb)] and large [1.5 to 2.0 kg (4.41 lb)] fruit and decreased the number of jumbo fruit (>2.0 kg). Total carotenoid concentration in mature fruit was unaffected by the defoliation or population treatments. Thus, butternut squash compensated for up to 33% leaf area loss at any time during the season. While the crop could compensate, under some conditions, for up to 50% plant losses, final plant population was more important than the growth stage of damage or defoliation for effects on crop yield.
Thomas F. Morris, George Hamilton and Sara Harney
There is little published data to support current recommended plant populations of 11,500 to 17,500 plants/acre (28,600 to 34,600 plants/ha) for fresh market sweet corn (Zea mays L.) in the northeastern United States. The plant population likely affects marketable yield and recovery of nitrate. Residual soil nitrate is of concern because of the potential for nitrate contamination of water supplies. Our objectives were to determine the effect of plant population on the yield of sweet corn grown for fresh market without irrigation and on the amount of nitrate in the surface 1 ft (30 cm) of soil at harvest. Seven main-season sweet corn varieties were planted in a total of eight experiments in 1995, 1996, and 1997. Seven experiments were in Connecticut and one was in New Hampshire. All but one of the varieties were standard (su) or sugary enhanced (se) varieties. The experimental design was a randomized complete block with four replications, and the treatments consisted of 12,000, 16,000, 20,000, 24,000, and 28,000 plants/acre (29,600, 39,500, 49,400, 59,300, and 69,200 plants/ha). The yield of marketable ears was classified based on the length of the ears. The results suggest that the current recommendations for plant population in the Northeast US may be too low. Populations of 20,000 and 24,000 plants/acre produced consistently greater yields of ears greater than 7.0 inches (178 mm) long. Soil nitrate-N concentrations at harvest were about 8 mg·kg-1 lower with 16,000 plants/acre or greater, compared with 12,000 plants/acre, which suggests that populations of 16,000/acre or greater should decrease the potential for nitrate contamination of water supplies in the fall, winter, and early spring.