There have been few comparisons of the performance of no‐tillage cropping systems vs. organic farming systems, particularly on erodible, droughty soils where reduced‐tillage systems are recommended. In particular, there is skepticism whether organic farming can improve soils as well as conventional no‐tillage systems because of the requirement for tillage associated with many organic farming operations. A 9‐yr comparison of selected minimum‐tillage strategies for grain production of corn (Zea mays L.), soybean [Glycine max (L.) Merr.], and wheat (Triticum aestivum L.) was conducted on a sloping, droughty site in Beltsville, MD, from 1994 to 2002. Four systems were compared: (i) a standard mid‐Atlantic no‐tillage system (NT) with recommended herbicide and N inputs, (ii) a cover crop‐based no‐tillage system (CC) including hairy vetch (Vicia villosa Roth) before corn, and rye (Secale cereale L.) before soybean, with reduced herbicide and N inputs, (iii) a no‐tillage crownvetch (Coronilla varia L.) living mulch system (CV) with recommended herbicide and N inputs, and (iv) a chisel‐plow based organic system (OR) with cover crops and manure for nutrients and postplanting cultivation for weed control. After 9 yr, competition with corn by weeds in OR and by the crownvetch living mulch in CV was unacceptable, particularly in dry years. On average, corn yields were 28 and 12% lower in OR and CV, respectively, than in the standard NT, whereas corn yields in CC and NT were similar. Despite the use of tillage, soil combustible C and N concentrations were higher at all depth intervals to 30 cm in OR compared with that in all other systems. A uniformity trial was conducted from 2003 to 2005 with corn grown according to the NT system on all plots. Yield of corn grown on plots with a 9‐yr history of OR and CV were 18 and 19% higher, respectively, than those with a history of NT whereas there was no difference between corn yield of plots with a history of NT and CC. Three tests of N availability (corn yield loss in subplots with no N applied in 2003–2005, presidedress soil nitrate test, and corn ear leaf N) all confirmed that there was more N available to corn in OR and CV than in NT. These results suggest that OR can provide greater long‐term soil benefits than conventional NT, despite the use of tillage in OR. However, these benefits may not be realized because of difficulty controlling weeds in OR.
The effects of UV‐B radiation on photosynthesis, growth and cannabinoid production of two greenhouse‐grown C. sativa chemotypes (drug and fiber) were assessed. Terminal meristems of vegetative and reproductive tissues were irradiated for 40 days at a daily dose of 0, 6.7 or 13.4 kJ m‐2 biologically effective UV‐B radiation. Infrared gas analysis was used to measure the physiological response of mature leaves, whereas gas‐liquid chromatography was used to determine the concentration of cannabinoids in leaf and floral tissue. There were no significant physiological or morphological differences among UV‐B treatments in either drug‐ or fiber‐type plants. The concentration of Δ9‐tetrahydrocannabinol (Δ9‐THC), but not of other cannabinoids, in both leaf and floral tissues increased with UV‐B dose in drug‐type plants. None of the cannabinoids in fiber‐type plants were affected by UV‐B radiation. The increased levels of Δ9‐THC in leaves after irradiation may account for the physiological and morphological tolerance to UV‐B radiation in the drug‐type plants. However, fiber plants showed no comparable change in the level of cannabidiol (a cannabinoid with UV‐B absorptive characteristics similar to Δ9 THC). Thus the contribution of cannabinoids as selective UV‐B filters in C. sativa is equivocal.
Growers of illegal Cannabis sativa L. use various cultural practices to maximize crop production. The objective of this study was to evaluate the morphological and biochemical responses of greenhouse grown C. sativa to soil incorporated N, P, and K as they reflect the geographical origin of Cannabis derivatives. Fertilizers were blended with Ap horizon soil from a Gilpin silt loam before placement in 12‐cm pots. NH4NO3‐N was applied at 0, 25, and 125 ppm. Phosphorus and K from super‐phosphate and KCI, respectively, were applied at 0, 50, and 150 ppm. Forty‐five‐day‐old anthesic Cannabis plants were harvested and combined leaf and flower tissues were analyzed for cannabidiol (CBD) and Δ9‐tetrahydrocanna‐binol (Δ9THC). Nine essential elements were also measured in plant tissue. Plant growth, tissue yield, and concentration of CBD and Δ9THC were positively correlated with extractable P2O5 (p < 0.01). Phosphorus concentrations in tissue were similarly related to yield of dry matter and cannabinoid concentrations. Uptake of K was positively correlated with extractable K2O across all treatment levels (r=0.40**), but was negatively correlated with tissue yield (r=‐‐0.36**). Growth and tissue yields were negatively related to total plant N (p< 0.01). Levels of extractable P2O5, Mn, B, and Mg were associated with specific concentration ranges for several plant elements plus Δ9THC. Thus, it was possible to partially characterize a soil by tissue analysis. For example, all of the plants grown on soil with less than 100 ppm of extractable P2O5 contained less than 8,000 ppm Δ9THC. Usefulness of such relationships will be dependent upon extensive evaluation of Cannabis on different soils under various cultural conditions. At this time, the reliability required for determination of origin of Canabis derivatives via chemical analysis does not exist when only essential elements and cannabinoids are considered.
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