1. Introduction

Cannabis sativa strains with a tetrahydrocannabinol (THC) concentration no greater than 0.3% in any part of the plant (Congress, [ Cannabis sativa strains with a THC concentration greater than 0.3% in any part of the plant are considered marijuana. Cannabis sativa contains over 100 cannabinoids, which include THC and CBD. It is well known that THC has psychoactive effects. Many have reported health benefits from marijuana, which may be associated with non-THC cannabinoids, such as CBD. The broad interest in CBD is for health benefits similar to marijuana but without the psychoactive effects of THC. Due to recent changes in legislation both at the federal and state levels, there has been a surge of interest in the growing, processing, selling, and using of products containing cannabidiol (CBD), derived from hemp flowers. Hemp is legally defined asstrains with a tetrahydrocannabinol (THC) concentration no greater than 0.3% in any part of the plant (Congress, [ 1 2 ]).strains with a THC concentration greater than 0.3% in any part of the plant are considered marijuana.contains over 100 cannabinoids, which include THC and CBD. It is well known that THC has psychoactive effects. Many have reported health benefits from marijuana, which may be associated with non-THC cannabinoids, such as CBD. The broad interest in CBD is for health benefits similar to marijuana but without the psychoactive effects of THC.

Hemp has historically been grown for fiber and seed, and due to recent changes in legislation, it is being grown for flowers. Hemp grown for flowers (floral hemp) follows a horticultural production model either in a greenhouse or bedded field compared to fiber and seed hemp, which follows an agronomic production model.

There is little published research investigating fertility requirements for floral hemp. As applied research is conducted to determine nutrient rates to maximize yield and minimize inputs, as well as to develop a target range of plant sufficiency ranges to aid in nutrient management, this study provides an invaluable basis to identify nutrient deficiency in the field and to develop sufficiency ranges where nutrient corrective action can be made before visual symptoms are expressed.

The impacts of plant nutrition on plant growth and yield, as well as plant primary and secondary metabolites, are well-established (Il’in, [ 3 ]). In hemp fiber varieties, Bosca et al. [ 4 ] reported higher levels of nitrogen increased plant leaf weight and decreased leaf THC content, presumably due to THC dilution. In a marijuana strain, phosphorus treatments had greater combined leaf and flower dry weight, as well as higher THC concentration, compared to the no phosphorus treatment (Coffman and Gentner, [ 5 6 ]). Hemp producers are seeking THC levels <0.3% and high CBD concentrations (i.e., 10–20%). Given the high energy and resource requirements for plants to produce secondary plant metabolites, such as cannabinoids (Taura et al., [ 7 8 ]), it would be reasonable to assume that nutritive disorders would impact the production and quality of these metabolites.

Plant tissue analysis has been used extensively for many decades to evaluate the nutritional status of a crop. Nutrient sufficiency levels (the tissue concentration at which growth or yield is not limited) have been established for most major agricultural and horticultural plants. Because cannabis has not been widely grown legally, nutrient sufficiency ranges have not been established. The development of sufficiency ranges for the essential plant nutrients would require extensive rate studies that measure both elemental concentrations in the leaf and the yield parameters of both floral biomass and cannabinoid concentrations. Where sufficiency ranges of a crop are not available, survey ranges can be used to approximate the nutritional status of the plant. Survey ranges for Cannabis sativa in greenhouse nursery production have been published by Bryson et al. [ 9 ], and more recently, a survey of five hemp cultivars in greenhouse production, including the cultivar used in this study, by Landis et al. [ 10 ]. These tissue values are useful for cannabis growers as they aid in fertility management. This study adds to this body of knowledge as the complete fertilizer controls can serve as an additional set of survey ranges for cannabis.

The second contribution of this study results in information about nutrient deficiency levels in the leaf tissue of cannabis. Once a plant begins showing visual symptoms of impaired growth, there is a reduction in plant health or yield is implicit. In this study, when plants began showing deficiency symptoms for each nutrient, most recently, mature leaf samples were analyzed for that nutrient. This information can be used by growers and researchers to confirm the visual diagnosis with leaf concentrations.

Additionally, no visual guides of nutrient deficiencies in cannabis supported with leaf tissue analysis and documenting a progression of symptomology have been published. Tracking the specific symptomologies of various nutritional disorders over time is important because symptomologies change in appearance and location as the deficiency progresses, making correct diagnosis challenging. Therefore, this study was conducted to provide cannabis growers and researchers with descriptions of nutrient disorders, high-quality images to track the progression of these disorders, and leaf tissue nutrient concentrations associated with documented deficiency symptomology.