The significance of the relationship between water, air, and growing medium is the least understood phenomenon for nursery crops and greenhouse production. Resultantly, a good number of plant loss can directly or indirectly relate to the improper relationship between these three essential cultural elements. It is essential to explore the basic understanding of these factors for the mediation of this relationship. It can be essentially valuable for the development of sound management practices for plant growth.
Solids and pore spaces are the essential components of growing mediums such as perlite, bark, and peat moss. The creation of the pores is due to the spaces is due to the components of the solid medium. So, a mix that is containing coarse aggregates has larger but fewer pore spaces than the other mediums made up of fine aggregates. The distribution and size of pores is the most critical factor for the development of the growing medium along with ensuring the optimal physical characteristics.
In most of the soilless growing media, the total pore space is constituting about 60-80%. About half a portion of the medium is occupied by air. As oxygen is the main requirement for the growth of plants so the maintenance of adequate aeration is significantly essential for the growing mediums. Roots do not only take oxygen for their normal processes, but they also release a good amount of carbon dioxide. Primarily, the exchange of gasses is happening by the process of diffusion through the growing medium. The pore space is the actual measurement of the ability to grow medium for holding the water and air. The rate of gas exchange and drainage can also be determined by the measurement of pore space. In the larger pores, the retention of the air followed by the irrigation is more. As the containers having the growing medium have a relatively greater quantity of water, so the percentage of air-filled pore space is greatly reduced. Therefore, it is essential to ensure the adequate distribution of small and large pore spaces. On average, 10-30% of air is present in most of the growing media.
In the growing medium, water is also present in the pore spaces. The availability of these water contents is greatly determined by the strength of binding with the solid components of the growing medium. When a water molecule is closer to the solid, then there are more forces of cohesion and adhesion between the solid and water molecule. So, as compared to the solid mix, the fine mix generally holds more amount of water, but its availability is less to the plant. Generally, in the soilless growing conditions, the amount of unattainable water is comparatively higher.
The shape of the container and pore size have significant effects on the drainage. The water in larger pores is almost freely available as the molecules of water are not much close to the solids of the growing medium. Resultantly, the availability of the water is increased to the plants. Additionally, the drainage of larger pores is also faster as compared to the smaller pores. The rate of drainage also has significant effects on the length of the soil column. In the taller containers, the force of gravity is also greater on the water contents that are occupying these pore spaces. In this way, the drainage is also increased.
The shorter columns which are having equal volumes as to the volume of the container, are generally holding more water, causes slow drainage, and comparatively contains less amount of air. The amount of drainage is also affected by the compaction. The number of larger pores can be significantly reduced by packing the growing medium into any feasible container. When this situation happens, the availability of water to the plants is automatically reduced, thereby reducing the gaseous exchange, aeration. Additionally, there is a significant reduction in the drainage, along with the increase in the water holding capacity. The compaction effects can be even more in smaller containers.
Water Holding Capacity
By the establishment of a balance between the drainage, aeration, and water holding capacity of any medium for plant growth, the optimum conditions for the best growth of plants can be ensured. Due to the higher costs of irrigations, the growers tend to use the mediums that can easily retain more water. Frequently, it results in the increased timing of the crop, poor root growth, and deteriorated quality of the products.
The amount of water that any medium can hold is strongly dependent on the use of essential components, size of pores, their distribution, and shape of the growing medium containing container. In the majority of the soilless growing medium, 60-70% of the water is drained.
Putting Together All Growing Mediums
By the development of effective planning for the management of irrigation, a careful match is required according to the specific needs of the plants. Mainly, the growers are more focused on the shortage of water in the growing mediums, but the results of various studies have indicated that some potential hazards are associated with the over-watering.
For the optimum growth of plants, aeration is the most important factor, and careful consideration is required for its management during the development of the growing medium. However, in the recent scenario, there is much pressure for the conservation of water that is greatly forcing the growers for the utilization of mixes that can hold a great amount of water. A better understanding of the relationship between water, air, and growing medium can be strongly helpful for the development and management of efficient growing mediums.
Table 1: Changing Effects of Size of Container and Compaction of Medium on Water and Air
|Degree of Compaction||4 Inches Container||6 Inches Container||1 Gallon Container|