Multipurpose Hemp crop

Industrial hemp (Cannabis sativa L.) or hemp production has recently been the subject of increasing interest around the world, especially in the United States. Hemp is a multipurpose crop that could also be grown for its fiber, seed, oil, food, and medicinal properties. Marijuana and hemp belong to the same plant species (i.e., Cannabis sativa). However, hemp is genetically different and also distinguished by its use and chemical makeup. More than 100 different chemical compounds called cannabinoids can be extracted from hemp. Two major cannabinoids are tetrahydrocannabinol (THC) and cannabidiol (CBD). Hemp contains THC of 0.3% or less, while marijuana can contain up to 20% THC, as its primary psychoactive chemical. Certain varieties of hemp have higher levels of CBD, the non-psychoactive part, that has medicinal properties ^[1].

Legalization

The interest in hemp and its benefits has spurred since significant changes in the legalization of hemp in the USA ^[2]. For decades, federal law did not differentiate hemp from other Cannabis plants. In 2014, the United States Congress granted permission through the Farm Bill to run test programs for growing hemp in a number of US states. Since then, 41 states have passed legislation that allows hemp cultivation. The 2018 Farm Bill declassified hemp from the list of controlled substances and legalized the production of hemp as an agricultural commodity ^[2]. According to the 2018 Farm Bill, hemp that is allowed to be cultivated should have a THC threshold of 0.3%. Due to an increase in demand for non-food crops and other food derivatives in the agricultural sector, hemp has progressively recovered its importance ^[3]. In the US, the amount of hemp acreage and licenses has increased rapidly in the last couple of years.

Value-added hemp

Hemp has the potential to be an environmentally friendly and highly sustainable crop if managed properly ^[4]. Hemp replenishes the soil and has been proven to remediate contaminated soils ^[5][6][7]. Generally, it is considered as a crop that could be grown without any pesticides ^[8] for certain varieties ^[9]. Hemp has the potential to suppress weeds efficiently and can fit well in a crop rotation ^[10]. Additionally, some residues of hemp can be used as botanical insecticides, miticides, or repellants within programs of pest management in organic farming ^[11]. These properties also make it suitable for integration in an organic farming system. Hence, the advantages of this crop in agriculture are not exclusively limited to its wide range of products and applications, but also due to its potential to improve soil health that encompasses the plant, environmental, and human health components.

Future prospects

Hemp production in the USA has been on the rise since the 21st century and more US states have attempted to establish a hemp production system following deregulation according to the 2018 US Farm Bill. This has significantly increased the potential for hemp markets in America. Many products can be derived from hemp, but the most enterprising situation for hemp in the USA is oilseed production and CBD extraction from hemp flowers for pharmaceutical uses. Although there is a renewed interest in the adoption of hemp, its production in the USA remains limited partly because of unclear agronomic guidance and fertilization recommendations, especially for CBD hemp in different soil and environmental conditions. Hence, it is essential to explore and update the scientific knowledge of hemp in order to understand and recommend the best management practices. Hemp cultivation requires intensive management, and environmental conditions like seedbed preparation, soil type, day length, seeding rates, dates, harvest dates, etc., are all impacted by the type of hemp variety employed. Hemp varieties grown for fiber, oil seed, and CBD have different fertilizer requirements and most of the fertility trials in the past have been limited to hemp for fiber. This review also describes the potential of integrating agronomic management practices intended to improve soil health like crop rotation, cover cropping, mulching, and manure application to hemp cultivation. Hemp is a potential emerging multipurpose crop with not only economic but also soil health benefits through phytoremediation, bio-sequestration, and bioenergy production.