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- Author or Editor: Ajay Nair x
Organic no-till and strip-till systems have gained attention because of their reported capacity to enhance soil health and suppress annual weeds. This study, conducted at the Horticulture Research Station, Ames, IA, over 2 years (2013–14 and 2014–15) compared a cover crop–based no tillage (NT), strip tillage (ST), and conventional tillage (CT) in transitional organic broccoli (Brassica oleracea L. var. italica) production, with data collected on broccoli yield and quality, plant health, weed suppression, soil temperature, and cost of production. A cover crop mixture of cereal rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth.) was seeded in all plots in September, and was ended by rolling and crimping (NT and ST) or soil incorporation (CT) in late spring the following year. Each whole-plot tillage treatment was split into two subplot fertility treatments—one based entirely on organic preplant granular fertilizer, and the other split between preplant granular fertilizer and postplanting fertigation—to test the effect of fertigation on yield and plant growth under the typically nitrogen (N)-limited reduced tillage conditions. In 2014, yield of broccoli was highest in CT treatments, averaging 5.4 t·ha−1, with no difference between ST and NT treatments. In 2015, yields were equal among tillage treatments, averaging 20.0 t·ha−1. Changing the timing of fertilizer application through the use of fertigation did not affect yield. Weed density and biomass were lowest in the between-row (BR) regions of NT and ST plots in 2014, indicating effective early-season weed suppression. In 2015, NT and ST plots generally had lower weed biomass and density compared with CT plots, but weed growth in BR and in-row (IR) regions of NT and ST plots was similar. Soil temperature was highest in CT plots throughout the year, and higher in ST than in NT plots only during some periods. While production costs did vary slightly across treatments, profit per hectare was most strongly affected by yield. Our findings suggest that cover crop–based organic NT and ST systems may be viable options for organic broccoli growers.
The area of organic production has registered a steady increase over past recent years. Transitioning to organic production is not straightforward and often includes a steep learning curve. Organic growers have to develop strategies to best manage nutrients, pests, and crop growth and yield. Additionally, in regions with temperate climate like the Great Lakes region, weather (especially temperature and solar radiation) plays an important role in crop productivity. Growers routinely use compost for nutrient provisioning and rowcovers for insect exclusion and growth enhancement. The objective of this work was to study the combined effect of rowcovers (with different light transmission) and compost organic cucumber (Cucumis sativus L.) growth and microclimate. Plots were assigned to three rowcover treatments (60% light transmission, 85% light transmission, and uncovered) and two amendment treatments (compost and no compost) in a split-plot factorial design. Data were collected for ambient air and soil temperature, photosynthetically active radiation (PAR), relative humidity, plant growth characteristics, and yield. Rowcovers modified crop microclimate by increasing air and soil temperature and decreasing PAR. There was a marked increase in the growing degree-day accumulations under rowcovers when compared with uncovered treatment. The impact of rowcovers on plant growth was significant. Use of rowcovers increased vine length, flower count, leaf area, leaf count, plant biomass, and total marketable yield. Use of compost in conjunction with rowcovers enhanced the rowcover effect. With the use of compost, there were not many significant differences in plant growth characteristics between rowcover materials; however, as expected, rowcover with 60% transmission was able to trap more heat and reduce light transmission when compared with rowcover with 85% transmission. This study clearly shows the importance of organic amendments, especially compost, in organic vegetable production. Applications of compost enhanced crop growth and also led to higher marketable yields. Results of this study suggest additive effects of rowcover and compost application on organic cucumber production.
Stewartias (Stewartia spp.) are prized for their camellia (Camellia japonica)-like flowers, intense fall color, and exfoliating bark. In spite of having outstanding ornamental value and features, these plants are not readily available for landscaping in the horticulture trade. The primary reason stated is the difficulty of its mass propagation and production. In the last two decades, considerable research has been conducted on various aspects of stewartia propagation such as seed germination, cutting type, light, rooting medium, rooting hormone, cold acclimation, and tissue culture. In this article, we discuss factors that directly influence propagation of stewartia and we highlight results of published studies to propagate stewartia. The evidence indicates success in adventitious rooting of cuttings but at the same time recognizes the continuing challenge associated with overwinter survival. Sexual propagation has also been studied, but its commercial application is limited. To date, there is lack of concrete information on why stewartia remains under-represented in our landscapes. It still remains unclear if it is the lack of consumer demand or existing propagation difficulties that is the cause of under utilization of stewartia. Given the information from most published studies, we suggest further research on the aspect of overwinter survival in addition to a survey of the nursery and greenhouse industry to accurately determine the cause behind the absence of stewartia in horticultural trade.
Cover crops can be used as a sustainable weed management tool in crop production systems. Cover crops have the ability to suppress weeds, reduce soil erosion, increase soil organic matter, and improve soil physical, chemical, and biological properties. In the north-central region of the United States, including Iowa, much cover crop research has been conducted in row crop systems, mainly with corn (Zea mays) and soybean (Glycine max) where cover crops are planted at the end of the growing season in September or October. There is little information available on the use of cover crops in vegetable cropping systems, particularly on the use of summer cover crops for fall vegetable production. The choice of the cover crop will significantly impact the entire fall vegetable production enterprise. Vegetable growers need information to identify the right cover crop for a particular slot in the cropping system and to understand how cover crops would affect weed suppression, soil properties, and successive vegetable crop yield. The time interval between cover crop termination and vegetable planting critically affects the growth and successive yield of the vegetable crop. This study investigated how short-duration summer cover crops impact weed suppression, soil properties, and ‘Adriana’ lettuce (Lactuca sativa) yield. The study also examined appropriate planting times of lettuce transplants after soil incorporation of cover crops. The experimental design was a randomized complete block split-plot design with four replications. Whole plots consisted of cover crop treatments: ‘Mancan’ buckwheat (Fagopyrum esculentum), ‘Iron & Clay’ cowpea/southernpea (Vigna unguiculata), black oats (Avena strigosa), ‘Grazex II’ sorghum-sudangrass (Sorghum bicolor ssp. drummondii), and a control (no-cover crop) where weeds were left to grow unchecked. The subplot treatment consisted of two lettuce transplanting times: planted immediately or 8 days after cover crop soil incorporation. Fall-planted butterhead lettuce was used. Data were collected on cover crop biomass, weed biomass, soil nutrient concentration, lettuce growth, and yield. All cover crops significantly reduced weed biomass during the fallow period as compared with the control treatment. Highest degree of weed suppression (90% as compared with the no-cover crop control treatment) was provided by buckwheat. Southernpea, a legume, increased soil nitrogen (N) concentration and contributed to higher lettuce yield and improved quality. Southernpea also enhanced lettuce growth and led to an earlier harvest than other treatments. Sorghum-sudangrass showed evidence of detrimental effects to the marketable lettuce crop. This was not due to N immobilization but presumably due to alleopathic properties. There is no clear pattern within any cover crop treatment that lettuce planting time following cover crop termination affects plant growth; however, planting early or soon after cover crop incorporation ensures more growing degree days and daylight, thus leading to timely harvest of a higher quality product. This study demonstrates that cover crops can successfully be integrated into vegetable cropping systems; however, cover crop selection is critical.
Biochar, a carbon-rich material derived from the pyrolysis of organic matter, exhibits beneficial chemical and physical properties when added to a soilless medium. Research on the use of biochar to improve plant productivity and growth has increased over the past decade, and has focused on using biochar as an alternative to sphagnum peatmoss. However, little work has been done to determine whether biochar can be used to partially replace commercially available sphagnum peatmoss–based greenhouse medium in vegetable transplant production. This study investigated the potential for supplementing a greenhouse growing medium with biochar for ‘Paladin’ pepper (Capsicum annuum) transplant production. Biochar was added to a soilless mix at rates of 0%, 20%, 40%, 60%, or 80% (by weight). Pepper seedlings were grown for 56 days in 50-, 72-, or 98-cell transplant trays at each of the five levels of biochar concentration. Germination increased in the 50- and 72- cell trays with 20%, 40%, and 60% biochar; however, biochar had no effect on germination in the 98-cell tray. Seedling height and dry weight decreased as biochar concentration and cell number increased. Seedling stem diameter also decreased with increasing cell number and biochar concentration. Leaf SPAD readings (indirect measurement of chlorophyll) decreased with increasing biochar rate. Medium pH increased with increasing biochar application rates. Higher rates of biochar (60% and 80%) increased pH well beyond 7.0 and negatively affected transplant growth. Overall results indicate positive effect of biochar in sphagnum peatmoss–based growing mix on seedling growth characteristics; although higher biochar concentrations could negatively affect seedling growth. Biochar can successfully replace up to 40% of sphagnum peatmoss–based growing medium and serve as a sustainable alternative medium in vegetable transplant production.
High tunnels allow vegetable growers to extend the growing season, increase crop production, and improve produce quality. Tomatoes (Solanum lycopersicum L.) are the most widely grown crops in high tunnels; however, tomato production in high tunnels can be challenging. Continuous cropping in high tunnels can increase soil-borne disease pressure and can lead to soil salinity or nutrient depletion issues. Based on preliminary research, we hypothesized that use of the rootstock ‘RST-04-106-T’ would increase yield and quality of heirloom and hybrid tomato scions compared with nongrafted plants. To test this hypothesis, our research objectives were to assess marketable yields, fruit quality and nutritional value, and plant growth of grafted and nongrafted hybrid and heirloom tomatoes in a high tunnel production system. Grafted and nongrafted ‘Cherokee Purple’ (heirloom) and ‘Mountain Fresh Plus’ (hybrid) tomatoes were grown in the same high tunnel for two seasons (7 May–20 Oct. 2015 and 29 April–7 Oct. 2016) at the Horticulture Research Station in Ames, IA. Grafted plants produced significantly more marketable fruit, although marketable and total fruit weight did not increase significantly. Individual fruit size was unaffected by grafting. Across cultivars, mean soluble solids content (SSC) in fruit was 0.3 °Brix lower in grafted plants as compared with the nongrafted control. Grafting did not affect lycopene content of fruit. Grafting increased stem diameter by an average of 0.8 mm, but overall plant biomass was unaffected. The effect of grafting on leaf chlorophyll concentration (SPAD readings) was mixed. In addition, grafting increased leaf chlorophyll concentration in ‘Cherokee Purple’ but decreased it in ‘Mountain Fresh Plus’ plants. Grafting is a valuable tool in tomato production, but the impact of ‘RST-04-106-T’ rootstock use appears to be specific to certain soil types with high incidence of bacterial wilt.
Euphorbia pulcherima Willd. ex Klotzsch (poinsettia) are grown commercially in all 50 states. This experiment was conducted to find a suitable media for cultivating `White Star' poinsettia under natural day-length conditions in Orono, Maine. The growth, morphology, and foliar and substrate nutrient concentration of `White Star' poinsettia was evaluated in three different media formulations (Promix®, Metromix-560®, and a 1:1 v/v mixture of Promix® and Metromix-560®). Results indicated minimal variability in overall plant height, but there were significant differences in the canopy area. Canopy area was greatest for plants grown in Promix® followed by a combination of Promix® and Metromix-560®. Plants grown in Promix® recorded the highest fresh weight (170.6 g). Bract area was statistically insignificant among the three treatments. Nutrient status of the media varied widely and was significant for nitrate–nitrogen, phosphorus, soluble salts, iron, calcium, magnesium, manganese, sodium, sulfur, and zinc. Foliar analysis revealed that nutrient concentrations also significantly differed across treatment media. Optimum media pH for growing poinsettia ranges from 6.0 to 7.5. Media pH for Promix® was 5.9, which was significantly higher than Metromix-560® (4.65) and Promix® + Metromix-560® (1:1 v/v; 5.3). In spite of significant differences in foliar and substrate nutrient concentrations, overall plant growth remained the same.
The natural distribution and cultivated areas of Stewartia taxa are USDA cold hardiness zones 6 or warmer. One cold-tolerant clone, named Stewartia`UMaine' (UMaine Silk Camellia), has been growing well at the University of Maine Littlefield Ornamentals Trial Garden (USDA Zone 4). The plant also has brilliant red fall color and biennial flowering. Since cold hardiness field evaluation could not provide genetic information and no other taxa could grow in Zone 4, AFLP markers were employed to figure out its genetic relativeness with other 16 named Stewartia taxa. The three primer-pairs generated 360 useful markers with an average of 120 markers for each taxon. The genetic distance between S. sinensis and S. rostrata is only 0.031, which indicates that these two species are very similar and should not be treated as two species or cultivars, at least the plants in cultivation. The largest distance (0.533) occurs between S. pesudocamellia and S. malacodendron, two distinguished species accepted by all taxonomists. UMaine Silk Camellia is a distinguished taxon from all other 16 taxa and S. malacodendron `Delmarva' has the largest genetic distance of 0.453 to it. Although S. ×henryae`Skyrocket' has the smallest genetic distance of 0.183 to Stewartia`UMaine', UPGMA phenograms showed that they are not in a clad at all. AFLP data support that Stewartia`UMaine' is a new cultivar, which originated from a gene pool of S. pseudocamellia, S. sinensis, and S. koreana. These molecular results will also be used as guidance for future Stewartia breeding.
In the last decade, organic production has been the fastest growing segment in U.S. agriculture. With increase in organic acreages there is a strong and growing demand for organically grown transplants. As a result of limited commercial availability of certified vegetable transplants, growers often produce their transplants on-farm. Commercial organic mixes for organic transplant production may not be locally available and are usually expensive. Growers often design their own mixes using compost and other organic amendments. The purpose of this study was to evaluate the incorporation of alfalfa-based amendment in a peat-compost medium for organic tomato transplant production. Growing medium of 2 peat:1 vermiculite:1 compost (by volume) was amended with 0%, 0.6%, 1.2%, 1.8%, or 2.4% weight by weight of alfalfa-based organic amendment and incubated for 0, 1, 2, 3, or 4 weeks. Medium pH and electrical conductivity (EC), seed germination (untreated Solanum Lycopersicon L. ‘Mountain Fresh’ seed), transplant dry weight, height, stem diameter, and SPAD values were measured. Medium pH increased with addition of alfalfa-based amendment but remained within the range of 5.5 to 7.0. Germination percentages were less than 50% in amended medium that was either not incubated or incubated for 4 weeks. Germination was greater than 75% if amended media were incubated for 1, 2, or 3 weeks. Seeds grown in peat-compost without any amendments had the highest germination rates; however, severe nutrient deficiency suppressed seedling growth. Relative to growth in medium with no amendments, plants growing in the amended medium had increased stem diameter, height, leaf chlorophyll content, and plant dry weight (90% to 160% more), provided the amended medium was incubated for at least 1 week. Application rate of 0.6% or 1.2% of alfalfa-based amendment produced transplants with suitable growth characteristics and met commercially acceptable standards for transplanting and handling at a reasonable estimated cost.
Stewartia pseudocamellia Maxim. (Japanese Stewartia), a member of Theaceae (tea family), is an excellent garden plant with ornamental features for all four seasons. Reproduction difficulty, however, limits its popularity. We conducted three experiments to ascertain the optimum conditions needed for rooting and subsequent overwintering of semihardwood Stewartia pseudocamellia cuttings. Cuttings were collected in July and prepared for rooting using two types of hormones (KIBA quick dip and Hormodin powder) and three media (Perlite + ProMix, Perlite + Perennial Mix, or Perlite + ProMix + Perennial Mix). Rooted cuttings were overwintered at four different temperatures. The best overwintering temperature was 5 °C, at which 65.6% of newly rooted cuttings survived. Temperatures lower than –12.2 °C were detrimental to the plants. Without cold treatment, only 21.9% of the rooted cuttings survived, which was three times lower than those that received 5 °C treatments. Plants rooted in Perlite + Perennial Mix had 61.8% overwintering survival, which is significantly higher than Perlite + ProMix. The quality of roots, indicated by total root length per cutting, was higher (104.3 cm) with Perlite + Perennial Mix, but not statistically significant. Cuttings treated with rooting hormones had higher rooting percentages (71.9% to 93.6%) as compared with the control (53%). For the same concentration (8000 mg·L−1), liquid (KIBA) and liquid + powder (KIBA + indole-3-butyric acid) rooting hormones resulted in better rooting percentages than powder (Hormodin) alone, although there was no statistical difference in rooting percentages among rooting hormone treatments. The best hormone for subsequent overwintering survival was the combination of quick dip (5000 mg·L−1 KIBA) and Hormodin #2 (0.3% a. i.; equivalent to 3000 mg·L−1). It resulted in 64.2% survival, significantly higher than for KIBA quick dip (8000 mg·L−1 a.i.) or Hormodin #3 (0.8% a. i.; equivalent to 8000 mg·L−1) alone. Our results suggest that reproduction (rooting and overwintering) of Stewartia was affected by many factors. We recommend rooting Stewartia in media that has good aeration and moderate water-holding capacity and overwintering them at ≈5 °C.