University of Kentucky ID-250 College of Agriculture, Food and Environment Cooperative Extension Service ndustrial hemp (Cannabis sativa L.) was at one time a major agronomic An Introduction to cropI in Kentucky. In A History of the Hemp Industry in Kentucky (1951), Industrial Hemp and author James F. Hopkins reported that it was a common crop on central Ken- Hemp Agronomy tucky farms from the late eighteenth and nineteenth centuries. Nearly all D.W. Williams, Plant and Soil Sciences, and farms growing hemp at that time were Rich Mundell, Kentucky Tobacco Research and Development Center mostly interested in the fiber it pro- duced. Farms with limited labor pools grew less or no hemp. It was a very labor-intensive crop both at harvest and during processing. Hemp became impractical as a crop in 1937 with the passage of the Marihuana Tax Act, which was an at- tempt by the U.S. federal government to reduce the production of Cannabis. The attempt to reduce production was largely due to the fact it was also being consumed as an intoxicant in addition to being utilized as a fiber crop. The new tax and licensing requirements made Cannabis production less prof- itable and much more bureaucratic, essentially ending production on large scales. There was a brief resurrection Figure 1. Industrial hemp plants grown for fiber at the UK Spindletop Farm. of hemp production during World War II, namely the Hemp for Victory or universities. In Kentucky, the Gen- are harvested for specific purposes, and campaign. During the campaign, U.S. eral Assembly had passed Senate Bill modern day hemp may be produced farmers were asked to grow hemp for 50 in 2013 in anticipation of the 2014 for one or sometimes dual purposes. fiber to be used in the war effort. In Farm Bill. Under those parameters, the Depending on the harvestable com- Kentucky, most hemp grown during the Kentucky Department of Agriculture ponent of interest, (i.e. fiber, grain, campaign was for seed to be shipped to (KDA) began administering the state- or cannabinoids) male plants and/or northern states where it was planted wide pilot research program in spring pollen might be vitally necessary or as a fiber crop. All Cannabis became 2014. The pilot research program in completely unwanted. fully illegal to produce or even possess Kentucky has grown each year since Today, there is not much need for following the passage of the Controlled and continues to grow today under the hemp rope or large hemp linens for Substance Act (often abbreviated CSA) management of the KDA. sailing ships, etc., as there was in the in 1978. Under the CSA, all forms of Cannabis sativa is a summer an- nineteenth century; however, fibers Cannabis were classified as Schedule nual plant that is strongly photoperiod- from hemp possess several very posi- 1 controlled substances and remain sensitive (flowers according to day tive attributes that may make them in that classification today. Other sub- length/photoperiod; not physiological useful as modern natural fibers. Uses stances under Schedule 1 classification maturity). It is mostly dioecious in for hemp fibers today are different and include the drugs heroin and cocaine. that male and female flowers occur much broader than when hemp was last The Agricultural Act of 2014, also on separate plants (i.e. there are both grown in Kentucky. Fiber from hemp known as the Farm Bill, provided for male plants and female plants). There stems can be utilized in numerous legal pilot research programs with are several monoecious commercial ways ranging from low tech yarn and industrial hemp to be administered by varieties (male and female flowers parts fabric to high tech electrical super- either state departments of agriculture on the same plant). Different plant parts capacitors manufactured from biochar.

Cooperative Extension Service | Agriculture and Natural Resources | Family and Consumer Sciences | 4-H Youth Development | Community and Economic Development Other potential uses of hemp fibers THC. This molecule could include alternatives for wood in is intoxicating and is construction materials (chip-board or responsible for the particle-board), strength-increasing high obtained from components added to concrete (hemp- using marijuana. crete), or fiber used in composite mate- By definition in the rials in place of synthetic fibers (molded, 2014 Farm Bill, the injected plastics). A complete list of the concentration of potential uses for hemp fibers is too THC (by dry weight) long to provide here. defines aCannabis The grain (seed) of hemp can also be plant as either mari- used in numerous ways. As a dietary juana (if it has more supplement for humans, it contains than 0.3% THC) or a very desirable ratio of omega-3 and industrial hemp (if Figure 2. Un-pollinated industrial hemp female flower from omega-6 fatty acids compared to it is at or below 0.3% the UK agronomic hemp research program. Note the white leaf many other potential sources. It is also THC). This is the hairs (trichomes). relatively high in both oil and protein only distinction be- contents. Hemp grain processors pro- tween marijuana and industrial hemp. flowers. Cannabinoids are found at duce a wide array of consumer products They are the same plant species and much lower concentrations in root, including raw hemp hearts, toasted look and smell exactly the same while shoot, and leaf tissues, and are not hemp seed, hemp seed oil, hemp flour, growing. A simple analogy might be found in significant concentrations in and even hemp coffee. It is also used to compare sweet corn and field corn. hemp seed, seed oil, or pollen. In the as bird feed and livestock feed in Eu- They are both Zea mays L. and look case of optimizing cannabinoid pro- rope, either whole or in part. Again, very similar, but the biochemistry is duction on a field scale, it is not known an entire list of potential uses of hemp very different between the two. The if the entire plant would be harvested grain is very long. A common practice same is true for marijuana and indus- and processed for cannabinoids, or just in regions where hemp is already being trial hemp. the female flowers. Field-scale cannabi- grown commercially is for producers to There are dozens of other naturally noid production could be a case where harvest hemp grain with combines and occurring cannabinoids besides THC. male plants are totally unwanted. The subsequently harvest the remaining One particular molecule, cannabidiol concentrations of cannabinoids in male stems for fiber similarly to harvesting or CBD, is currently of deep and broad plants is very low compared to female a hay crop. This is the most common interest among pharmaceutical and flowers. Also, it is reported anecdot- example of a dual-purpose industrial medical researchers. Cannabidiol ally that unfertilized (un-pollinated) hemp crop. Of course, if hemp does is reported to have strong potential female flowers tend to produce more become a viable commodity crop in for pharmaceutical applications. For cannabinoids than when they are pol- Kentucky and the U.S., seed produc- example, certain epileptic patients linated and allowed to produce seed. As tion, especially certified seed for estab- treated with CBD experience reduc- a result, in clonal propagation systems lishing next year’s hemp crops, could tion in the frequency and severity of where all female plants are established, be an excellent option for Kentucky seizures. There are other proposed, attempts would be made to prohibit producers. Our soils, climate, and exist- positive effects of CBD. Examples male plants near the production field. ing infrastructure are very conducive to include potential uses as an analgesic, Experiments are under way at UK to hemp seed and grain production. appetite enhancer, and anti-depressant. quantify the effects of pollination on Cannabinoids are another harvest- Many of the cannabinoids identified cannabinoid production in both indoor able component of Cannabis plants. to date have not been studied for their and outdoor production systems. Early They are plant-generated molecules potential as pharmaceutical agents. It results support the anecdotal premise that are known to have certain sig- is also thought that some number of that un-pollinated female flowers nificant effects on humans. Cannabi- cannabinoids remain to be identified. produce more cannabinoids than pol- noids are mainly, but not exclusively, Cannabinoids are present through- linated flowers. However, this work produced by plants in the genus Can- out the plant but are mostly concen- must be repeated to provide a strong nabis. The most familiar cannabinoid trated in tissues from female flowers, level of confidence in the results, and is delta-9 tetrahydrocannabinol, or especially in the leaf hairs of female will be published as soon as that can be accomplished.

2 Table 1. General agronomic recommendations for the main harvestable components of General Production industrial hemp Information Grain/Dual It is important to note that from Fiber Purpose Cannabinoids* the early twentieth century until 2015, Seeding rate (PLS) 40-60#/A 30-40#/A 30-40#/A there have been no U.S.-based agro- Row spacing 8 inches 8-16 inches 8-16 inches nomic research studies with industrial Soil pH 6.2-6.5 6.2-6.5 6.2-6.5 hemp. Information from historical re- Applied nitrogen 50 lb/A 100 lb/A 50-100 lb/A search is important and useful but Available phosphorus 60 lb/A 60 lb/A 60 lb/A may not always be directly applicable Available potassium 300 lb/A 300 lb/A 300 lb/A to modern production systems. It is Harvest timing 420 0 continues to conduct basic agronomic High >60 0 355-420 0 trials with varieties grown for all three 336-354 0 318-335 0 harvestable components (fiber, grain, 301-317 0 and cannabinoids). Until the informa- Medium 46-60 30 282-300 30 tion from these and other replicated 41-45 40 264-281 30 research trials in the U.S. is available, 37-40 50 242-263 30 we must rely on previous U.S.-based re- 33-36 60 226-241 40 28-32 70 209-225 50 search and more recent research from 191-208 60 other countries to make production Low 23-27 80 173-190 70 recommendations (See Tables 1 and 2). 19-22 90 155-172 80 14-18 100 136-154 90 Basic Terms and Definitions 9-13 110 118-135 100 Pure live seed (PLS) is the seed in a 6-8 120 100-117 110 container that will likely produce a vi- Very low 1-5 200 <100 120 able plant when planted appropriately Source: UK Cooperative Extension publication 2018-2019 Lime and Nutrient Recommenda- tions (AGR-1) (depth, timing, etc.). Recommended seeding rates are always expressed as pounds of PLS/A. All containers (non-crop seed) along with the ger- rates, we need to increase the amount of seed will have a mass or weight of mination percentage of the crop seed of seed planted by 30 percent above the materials in addition to PLS. This is defines PLS. For example, a container recommended seeding rate (5%+25%; usually expressed as a percentage of the includes 5 percent non-crop seed and the sum of non-crop seed and crop total weight in the container. Examples has a germination rate of 75 percent. seed that will likely not germinate). include inert materials (soil, chaff, and This means that 5 percent of the weight For example, if the recommended other plant parts) as well as seed that of the material in the container is not seeding rate is 60 pounds of PLS/A, will likely not germinate (immature crop seed and that only 75 percent we divide the seeding rate (60) by the or dead seed). Other contributions to of the crop seed will likely germinate PLS percentage (0.70 which equals reductions of PLS in a container are and produce a new plant. In order to 70%). The result is we would need to other crop seeds and weed seeds. The calculate the amount of seed needed to apply approximately 86 pounds of this percentages of inert or other materials accommodate recommended seeding particular seed per acre to achieve the

3 60#PLS/A seeding rate. If germination percentages are not provided, it would be wise to have a germination test per- formed prior to seeding. This is true even if non-crop seed percentages are not available. We have witnessed very poor germination of some hemp variet- ies and have received several anecdotal reports of the same. Poor germination equates to poor stand establishment. Poor establishment leads to increased weed pressure, reduced yields, harvest- ing problems, or crop failures. Using the proper seeding rates based on PLS is imperative for successful hemp es- Figure 3. Drilling a hemp fiber crop at the UK C. Oran Little Research Center. tablishment and harvest. We note, too, that the 1,000-seed weights vary signifi- cantly among hemp varieties. We are working on recommendations based on the number of plants per square meter for successful establishment rather than pounds of seed per acre. The 1,000-seed weights can sometimes differ by two times among varieties, which would have a highly significant impact on plant populations and suc- cessful establishment. Nutrient application rates are ex- pressed as units or pounds of nutrient per acre. The amount to apply using a specific fertilizer is calculated by divid- ing the desired nutrient application Figure 4. Harvesting hemp grain by combine at the UK C. Oran Little Research Center. rate by the analysis of the fertilizer. For example, to apply 50 pounds/units of nitrogen (N)/A using urea (46-0-0), we equal to current grain crops. If maxi- maximum yields and a crop that is divide 50 by 0.46 (46% N in urea) which mum yields are not the goal, industrial harvestable with standard equipment. equals approximately 109 pounds of hemp can be expected to perform on Producers should research varieties urea applied per acre. marginal lands with lower productiv- based on the harvestable component ity and with reduced inputs much the of interest (fiber, grain/fiber, or can- Site Selection and Inputs same as our current commodity crops nabinoids) and choose varieties that Although industrial hemp has been would. are proven performers. Hemp seed touted as a low-input crop that is highly Varietal Responses produced in Kentucky and certified adaptable to marginal lands, the scien- under the Association of Seed Certi- tific literature from other countries as Variety selection will be key to fying Agencies (AOSCA) guidelines well as research at UK clearly indicates success for many reasons, most im- will be available beginning in 2018. that maximum yields are realized with portantly days to maturity (latitudinal We expect domestic certified seed inputs equivalent to current grain adaptation). There is much to know production in Kentucky will continue production systems (e.g., corn) and on about selecting the proper variety. For to increase. Standard industrial hemp productive land (>170 bu/A corn). If example, varieties bred primarily for variety trials are conducted at UK an- maximum industrial hemp yields are grain production could have signifi- nually. The reports are posted on the the goal, select good corn land (deep, cantly different maturity dates relative UK agronomic hemp website at: http:// well-drained soils) and plan on inputs to each other, and therefore would have hemp.ca.uky.edu/. very different establishment dates for

4 maturity. Optimal, field-scale can- nabinoid production systems are not yet well-defined. Lacking appropriate research-based information, cannabi- noid production from seed should be thought of similarly to grain produc- tion. In very general terms, industrial hemp seed can be planted in late April or early May in Kentucky. Seedling in- dustrial hemp is tolerant of light frosts, but it is probably best to avoid the last killing frost while still taking advantage of good soil moisture and adequate soil temperatures common in spring.

Figure 5. Mowing a hemp fiber crop at the UK C. Oran Little Research Center. Pesticides There are currently no pesticides (herbicides, insecticides, fungicides, nematicides, etc.) labeled for use in industrial hemp crops in the U.S. This is true for both indoor and outdoor (field-scale) production systems. This means that any pesticide applications to industrial hemp crops are off-label and therefore illegal. Work is under way to evaluate pesticides for use in industrial hemp production systems and also to investigate several options for emergency exemptions within the rules and policies of the U.S. EPA. Today, it is imperative to make good management decisions to reduce the Figure 6. Baling a hemp fiber crop at the UK C. Oran Little Research Center. negative effects of pests, particularly weeds. Variety selection, soil moisture Establishment from Seed and moisture at planting will help ac- at planting, seeding dates, seeding rates, It appears that industrial hemp complish this. Planting depth should and fertility are examples of manage- seed is quite sensitive to a lack of soil never exceed one inch (1”), and 0.5 to ment decisions that will potentially moisture at planting. This trait has 0.25 inch is preferred. Industrial hemp reduce competition from weeds and not been quantified but could read- seed can be successfully drilled with increase yields without herbicides. To ily contribute to stand failures. Seed both conventional tillage and no-till date, we have not witnessed significant should be planted in soils with adequate protocols. Seeding dates will depend pressure from insect or disease pests in moisture to encourage rapid germina- equally on the harvestable component field-scale production systems for fiber tion. If soil moisture is inadequate for (fiber, grain, or cannabinoids) and the or grain. We are aware of reports of industrial hemp germination, it is likely variety. Fiber crops will be harvested disease issues in field-scale cannabinoid still adequate to support the germina- at the onset of reproductive growth productions systems, especially when tion of many weed seeds. Without the and should be planted as early as pos- clones are used as transplants. There availability of labeled herbicides for sible to maximize vegetative growth have been serious reports of both dis- industrial hemp production systems, (biomass production). Days to maturity ease and insect pests in indoor growing we rely heavily on rapid hemp canopy of grain crops will vary a great deal systems in Kentucky. development and closure to reduce or among varieties. As such, some grain eliminate competition from weeds. varieties should be planted much later Adequate soil temperature (>/=50oF) than others to manage crop height at

5 Harvest Protocols microbial activity. The equipment for Additional Information optimal cutting and then management Harvesting industrial hemp grain by Economic Considerations for Grow- of the crop during retting does not yet combine is the norm in other countries ing Industrial Hemp: Implications for exist in the U.S. Additionally, field- and has been accomplished success- Kentucky’s Farmers and Agricultural retting industrial hemp will require fully in Kentucky. Again, variety selec- Economy. Department of Agricultural new skills remotely similar to those tion is key as the growth habits of those Economics, University of Kentucky. involved in making high-quality hay. varieties bred primarily for grain pro- July 2013. https://www.uky.edu/Ag/AgE- Successful field retting will be totally duction are more conducive to harvest con/pubs/reshempimpfarmer28.pdf. by combine. Grain from varieties bred dependent on weather conditions just as is making good hay. Over-retting primarily for fiber production could be Industrial Hemp Production. UK Cen- will dramatically reduce the quality very difficult or perhaps impossible to ter for Crop Diversification, University of the fiber. Under-retting will make harvest efficiently by combine, espe- of Kentucky. September 2015. http:// cially if planted early. Harvesting fiber processing inefficient or impossible. www.uky.edu/ccd/sites/www.uky.edu.ccd/ Harvesting hemp stems for fiber with crops is more complex. Fiber crops files/hempproduction.pdf. will nearly always require retting prior standard hay equipment can be diffi- to baling. Retting is essentially a quasi- cult. Current thinking involves mowing controlled rotting process. During by sickle-bar or mower-conditioner retting, microbial activity breaks down without conditioning/macerating, the pectin layer between the bast and retting in the field, followed by baling hurd fibers thus allowing for efficient (round or mid-size/large square). Op- separation. Microbial activity will timal harvest and processing/storage be very sensitive to temperature and methods for cannabinoids are not well defined in field-scale systems. Research Photos: Rich Mundell and D.W. Williams, moisture. Generally speaking, warm Figure 2. All others, Matt Barton, Ag Com- and moist conditions will encourage is on-going at UK to address all of these munications. questions.

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