Abstract
Horticulture involves growing crops and ornamental plants in indoor and outdoor environments. Horticultural crops include food crops such as vegetables and fruits (including tree fruits, small fruits and grapes), as well as nut- and seed-bearing plants, herbs and spices. Many non-food crops are also managed by horticulturalists, including medicinal plants, tobacco, hemp, ornamental plants and flowers. Horticultural crops grow naturally in temperate, sub-tropical and tropical climates of the world, although many of these crops are sufficiently robust that they can be grown in any suitable controlled environment. In 2015, astronauts on the International Space Station grew, harvested and ate red romaine lettuce from their VEGGIE system (Vegetable Production System), which has successfully produced lettuce, Swiss chard, radishes, Chinese cabbage and peas in simulated space environments. The VEGGIE is equipped with adequate lighting, water and nutrients to grow vegetables, relying on the space station's cabin environment for temperature and pressure control, and as a source of carbon dioxide for plant growth (NASA, 2016). Most horticultural crops are planted in soil, although modern cultivation techniques include other media, such as peat-based soil, compost, and inert substrates such as rockwool. A suitable growing media must provide anchorage and stability for the plant roots, considering the diverse life histories of horticultural crops. For example, plants that complete their life cycle in one (annual) or two (biennial) growing seasons does not produce the extensive, deep root system of a woody perennial that lives for several decades. Without adequate anchorage, shrubs and trees are vulnerable to blow down in wind-storms if their roots are in loose, fluid soils or if the plant has a shallow root system on a rocky strata close to the surface. Wind rocking of a poorly-anchored seedling can lead to fine roots breakage and root system detachment from soil, causing the plant to tilt. Soil management refers to the way that soils are cultivated to support horticultural crop growth. Actively growing roots need oxygen for their metabolic function, so the soil must have a crumbly, porous structure that allows for gas exchange with the atmosphere. The porous soil structure permits oxygen diffusion to the root zone, and for carbon dioxide respired by the roots to leave the soil environment. Since plants roots are responsible for obtaining most of the water required for metabolic functions and cooling leaf surfaces, the soil must retain and supply water to the roots while avoiding waterlogging, which inhibits root functions. Soil also provides many essential plant nutrients for crop growth, such as nitrogen, phosphorus, potassium, calcium, magnesium, sulfur and micronutrients (boron, iron, copper, manganese, zinc, chloride, molybdenum and nickel). Nutrient uptake in the root system is facilitated by plant interactions with soil-dwelling microorganisms, both free-living and symbiotic, which are abundant in the root zone. Good soil management is essential to produce nutritious, high yielding food and to support the growth of non-food crops like herbaceous and woody ornamentals. Soil management specialists are responsible for maintaining the soil physical integrity, its chemical balance and soil microbial life necessary for growing horticultural crops.
From Agronomy to Horticulture: The Diversification of Hawaii's Agriculture