Browse

The impacts of weed interference on hemp (Cannabis sativa) yield are largely unstudied despite causing serious economic losses in most cropping systems. For high-cannabidiol (CBD) hemp, understanding the role of weed competition on CBD and tetrahydrocannabinol (THC) content may help promote profitability and regulatory compliance. Therefore, we tested the effects of varying waterhemp [Amaranthus tuberculatus (zero, one, three, and five waterhemp plants per planting hole)] and hemp (zero or one hemp plants per planting hole) planting densities on total hemp yield, chemical composition, and aboveground waterhemp biomass in plasticulture. There was no significant total biomass or stripped floral biomass yield loss resulting from waterhemp competition, although unexpectedly high variation in hemp phenotypes likely limited the ability to detect subtle differences between treatments. Furthermore, there was no significant effect of competition treatment on total CBD, total THC, or measured terpene composition. However, waterhemp biomass was reduced significantly by competition from hemp in comparison with hemp-free treatments. Suppression of waterhemp by hemp and lack of significant yield loss suggest that hemp can be highly competitive and grown successfully without herbicides in certain circumstances.

Black cumin (Nigella sativa) is an important medicinal plant in the pharmacological industry. It is cultivated on a commercial scale, but its seeds have a slow, unsynchronized germination rate. Enhancing seed germination is crucial for improving the production of black cumin. The influence of presowing treatments [gibberellic acid (GA₃), potassium nitrate, salicylic acid, and stratification at 4 °C] on seed germination was assessed. Seed germination was determined daily for 30 days, and germination parameters, including final germination percentage (FGP), corrected germination rate, number of days to reach 50% of FGP, and seedling length vigor index, were evaluated. Endogenous contents of GA₃ and abscisic acid (ABA) in nonstratified and stratified seeds were estimated using high-performance liquid chromatography (HPLC) and seedling growth was determined in 45-day-old seedlings. All presowing treatments tended to boost early germination for the first 10 days compared with the control. Low concentrations of GA₃ at 0.25 g·L⁻¹ also increased FGP (80%) compared with the control group (65.55%). Stratification for 4 weeks provided the greatest FGP value at 95.56%, and stratification for 3 weeks proved to be the most effective treatment for optimal seedling growth. Sodium dodecyl sulphate–polyacrylamide gel electrophoresis patterns of stratified seeds revealed the alteration in intensities of 13 bands and the appearance of a new band (180 kDa) indicating a change in the synthesis of proteins during stratification. Moreover, stratification modulated the endogenous GA₃ and ABA contents of black cumin seeds, which alleviated the physiological dormancy and resulted in high and synchronized seed germination.

Small-scale vegetable farmers are interested in cover crops and reduced tillage, but scale-appropriate technology and equipment are necessary to expand these practices to the growing segment of small farms. We sought to determine the efficacy of tarps, an increasingly popular tool on small farms, to end overwintering cover crops and provide weed suppression for subsequent no-till cabbage production. In three fields over two seasons in Maine, we grew a winter rye (Secale cereale L.) and hairy vetch (Vicia villosa L.) cover crop, which we managed by a factorial combination of tillage (no-till, till) and tarping (tarp, no-tarp) in June, followed by a transplanted cabbage crop (Brassica oleracea L. var. Capitata) in July. Within each treatment, subplots were either weeded by hand or left unweeded. Cover crop biomass ranged from 2.8 to 4.5 Mg⋅ha⁻¹. Mean cabbage weights in the novel no-till system (no-till/tarp) were greater than (year 1) or equal to (year 2) those in tillage-based systems (till/no-tarp and till/tarp). In year 1, the mean cabbage weight in weeded subplots was 48% greater in no-till/tarp than in till/no-tarp systems. In unweeded subplots, this difference was 270%, highlighting the efficacy of the no-till/tarp system to reduce the impact of weeds. In year 2, weed biomass was higher with all treatments than it was in year 1, and unweeded subplots failed to produce marketable heads (i.e., >300 g). The mean cabbage weight in weeded subplots was equal among no-till/tarp, till/tarp, and till/no-tarp systems. Tarping had a strong effect on weed biomass and weed community composition measured at the time of cabbage harvest in unweeded subplots. In year 1, weed biomass at the time of cabbage harvest with tarp treatments was less than half that with no-tarp treatments. Tarps effectively facilitated the cover crop mulch-based no-till system. We propose that this system is an adaptive strategy for farmers affected by climate change. However, both cover crop production and tarping shorten the growing season. We discuss tradeoffs and opportunity costs using the metric of growing degree days.

Creeping bentgrass (Agrostis stolonifera) is a desirable turfgrass putting green species that is susceptible to drought stress. Planting drought-resistant creeping bentgrass will enhance the resilience of golf turf surfaces, lower required resource inputs, and reduce the environmental impact of golf courses. Creeping bentgrass cultivar performance data during drought stress are needed for informed selection of appropriate cultivars. We evaluated the drought performance of 19 cultivars of creeping bentgrass and found that newer creeping bentgrass cultivars such as Pure Distinction and others exhibited superior drought performance compared with older cultivars such as Penncross and L93 based on turf quality, photochemical yield, and leaf relative water content. The results of this work should be used to aid in the selection of drought-resistant creeping bentgrass cultivars for turfgrass practitioners.

Analysis of composite pecan leaf samples typically used to determine need for nutrient applications does not account for variability among trees in the sampled area. To account for this unmeasured variability, pecan orchard block nutrient standards are greater than actual single tree nutrient requirements. In 2018 and 2019, we measured variability in a pecan orchard block by evaluating nutrient status of all trees in a study area consisting of two cultivars (Wichita and Western) grafted on open-pollinated ‘Ideal’ seedlings. Foliar zinc (Zn) coefficient of variation (cv) ranged from 0.186 to 0.255 within individual cultivars and years but was as high as 0.30 when combining cultivars within a year. The ‘Western’ cultivar had higher foliar Zn concentrations than ‘Wichita’, but Zn concentrations were not consistently associated with other leaf nutrient levels, soil Zn status, or other soil properties. Using observed foliar Zn variability, we determined that it is necessary to sample 35 trees for a composite sample to achieve a relative margin of error of 10% and 95% confidence level in a pecan orchard block with more than 1000 trees. We developed field scale foliar Zn recommendations based on individual tree research that indicates a minimum acceptable leaf Zn concentration of ≈15 mg·kg^–1 is needed to maintain optimal photosynthetic function in Zn chelate fertigated pecan trees. Assuming a Zn cv of 0.30 and a composite sample comprised of leaves from 35 trees, the minimum acceptable orchard block Zn level to ensure that less than 5% of trees had suboptimal levels of Zn was 27.6 mg·kg^–1. An orchard block Zn level below 23.4 mg·kg^–1 indicates that more than 5% of trees in the block had suboptimal foliar Zn concentrations.

Abstract

A rootstock collection of Prunus species and hybrids is maintained at the U.S. Department of Agriculture stone fruit breeding program at Byron, GA. We genotyped 66 Prunus rootstock accessions and clones using chloroplast and nuclear microsatellites in this study. Chloroplast microsatellites revealed that the accessions belong to four previously defined maternal lineage groups (MLG-1 to -4) and five new ones (MLG-9 to -13). MLG-1 and -2 share the same chloroplast alleles of ‘Chinese Cling’ peach (Prunus persica) derived scions and American scions and rootstocks related to early European introductions, respectively. MLG-3 included ‘Guardian’ rootstock and its descendants. MLG-4 had a single genotype, ‘Okinawa’, that is the maternal parent of ‘Flordaking’. MLG-9 and MLG-11 to -13 included hybrids with different plums (Prunus salicina, Prunus cerasifera, Prunus tomentosa, or Prunus angustifolia) in their maternal parentage. MLG-10 included hybrids from almond (Prunus. dulcis) in the maternal parentage. The neighbor-joining phylogenetic tree based on nuclear microsatellite genotyping data showed several clusters. Cluster I included only one scion cultivar Elberta from MLG-1. Clusters II, III, and V contained peach accessions mostly in MLG-2. Clusters IV and VI included accessions mostly in MLG-3. Cluster VII included most accessions of plum-peach hybrid origin and those found within MLG-13. Cluster VIII was found to be mixed with different plum-peach hybrids and hybrids from other Prunus species, most of which were found in MLG-10, -11, and -12. Most accessions in Cluster IX were related to plums in MLG-11 and a few accessions in MLG-9.