1. Introduction
Studies have been carried out to test the effectiveness of various hydroponics growing substrates in the growth and yield of cut roses production. This review will introduce the cut-flower industry, soilless culture system, characteristics of commonly used medias and discussion on the different medias used in rose cultivation.
1.1 Introduction to cut-flower production
Flowers are known to be able to lift the mood and atmosphere of a room, bringing positive emotions to people. Certain flowers convey passion, sympathy, celebration, making them a great gift for various occasions such as Valentine’s Day, funerals, marriage etc. The increase in popularity of cut flowers result to the rise in cut flower production throughout Eastern Africa, Southern & Central America, Asia and the Middle East. Developed countries, Europe, America and Asia account for the demand in floriculture trade. The main suppliers in the floriculture sector are Asia-Pacific countries, African, Middle Eastern, Colombia, Ecuador and other European countries.
Over the recent years, global exports have grown exponentially. A 24% growth about USD 4 billion in 2012 compared to 2010, was achieved in developing countries. Also, an increase of export value of cut flowers in Sub-Saharan Africa from USD208m to USD568m from 2011 to 2012 respectively. However, it was reported that Australia’s floriculture industry will gradually decline by 1.3% annually for five years through 2013-2014, putting the floriculture production industry on the edge, facing competition with the rising imports due to cheaper production cost resulting to a decline in demand of cut flowers grown locally, depleting export profits.
1.2 Hydroponics system
With the continuous rise in urbanization and industrialization due to the increasing human population, one of the major challenges faced in the near future would be the declining of land availability. Resulting to a risk in food security, unable to feed the increasing population due to the decrease in arable land for agriculture production.
The adoption of soil-less culture has been increasingly popular in the agriculture industry and helps to face the challenge of lack of arable land for cultivation.
There are 2 techniques of soil-less culture, hydroponics and aeroponics. In a hydroponics system, plants are grown in mineral solutions without soil in a controlled environment. By using this system, issues with abiotic factors, climate and weather can be eliminated, also it allows the monitoring of nutrients and water supplies, providing the crop with optimal condition, increasing productivity and product quality. Water is one of the most common limiting factors in crop production, however in hydroponics system, the nutrient solution can be recycled thus reducing water losses from the production. (Ketter 2015). In comparison to soil-based agriculture, the advantages of hydroponics system greatly outweigh its disadvantages. However, despite the many advantages, soil-less culture has its limitations. The start-up cost of the system is high and requires technical knowledge, also requires energy to run the system.
The introduction of hydroponics has shown positive results all over the world
In recent years, growers began using hydroponics system for cut flower production as length of day, temperature, pH can be controlled, aiding in the blooming vigour of the plant. (Sardare & Admane 2013)
Some cut flowers that can be grown hydroponically are Tagetes patuala (Marigold), Dianthus caryophyllus (Carnations), Chrysanthemum indicum (Chrysanthemum), however Rosa berberifolia (Roses) would be focused on in this review.
1.3 Rosa berberifolia (Roses)
Rose is a most loved traditional flower and has been a popular cut flower in the global floriculture trade. There are over 150 species under the genus Rosa breed by plant breeders and amateur gardeners. Rose requires a rich in minerals and organic matter loamy soil and a pH between 6 to 6.5 for cultivation (Das et al. 2012). However, in soil-less culture, rose are normally grown in inert media such as perlite, cocopeat, rockwool, etc. In this review, the effect of different hydroponics media used and the productivity of the roses, in terms of flower size and stem length which are the two important factors that dictate the value of cut-flowers, would be evaluated.
2. Characteristics of different hydroponic medias
There are 2 kinds of hydroponics system water culture and aggregate culture, where inert materials such as rock wool, perlite, vermiculite, cocopeat, etc., are used as a medium. An ideal medium for the system would be one that maximizes root and shoot growth, with perfect ratio of air to water space, allowing nutrient uptake, adequate drainage and water holding capacity (Bisht et al. 2013).
2.1 Rockwool
Rockwool is one of the commonly used substrate in hydroponics. Rockwool is sterile, inorganic, lightweight and has high water holding capacity, which can also be one of its limitation. As high absorbance of water could result to low oxygen concentration in rockwool leading to suffocation of the plants roots, causing detrimental effects such as stem and root rot (Bhattarai et al. 2008).
2.2 Coco peat
Coco peat is another one of the widely used substrates in horticultural production, made from the outer husk of coconuts. It has a high liquid and gases absorption rate due high surface area per unit volume resulted from its honeycomb structure (Cresswell 2002; Ketter 2015). Also, coco peat has good drainage properties but able to retain enough moisture to facilitate plant growth.
2.3 Perlite
Perlite has a neutral pH, high porosity, light weight and good absorbance. It is commonly mixed with other growing mediums, but can also be used on its own. Perlite is preferred in carrot cultivation (Asaduzzaman et al. 2013), as it encourage root development, has good drainage and balanced ratio of air to water.
3. Discussion
Various studies have been carried out to identify the best hydroponics medium for rose productivity. What constitutes a good medium? Besides looking at the EC, pH, water holding capacity, porosity, and other chemical properties, the sustainability and availability of a medium should also be taken into consideration and the constraints or effects it has on the environment.
Rockwool slab and perlite were commonly used for rose cultivation in Korea (Choi et al. 2009). Moreover, in a study (Han et al. 2014) tested the productivity of roses in four different mediums, perlite, rockwool slab, phenolic foam LC slab and phenolic foam RC slab. Results showed that the longest stem length and most number of cut flowers obtained during harvest was produced in rockwool slab. Even though rockwool has shown promising results in rose cultivation, rockwool is artificial and non-sustainable, resulting to declining availability and high cost of quality rockwool. Thus, there is a need for a cheaper and sustainable alternative substrate.
A study found that growing media affected yield and qualitative traits of the crop (Fascella 2009). Results showed that plants grown in mixture of perlite and coconut coir produced the best result in terms of number of flowers, length and thickness of the stems as compared to pure perlite. This might be related to the water holding capacity and cation exchange capacity of coconut coir. Another study had also achieved similar results (Rezaee et al. 2013).
On the other hand (Ketter 2015) paper stated that with the use of coco peat in aggregate culture, the pH becomes more acidic, from 5.8 to 4.8, during reproductive stage and at harvest respectively. Whereas in rockwool granulate, the pH increases from 5.8 to 6.7. Though there is a change in pH, it can be adjusted through nutrient solution to suit crop requirements.
Rice hulls, another agriculture waste besides coco peat, mixed with press mud, have proved to improve yield and quality of cut roses (Ahmad 2009). Rice hulls can be obtained from rice industry and are sterile from the steaming process and is ideal to be used as a medium due to its large pores, increasing oxygen concentration at the roots.
Another study (Chimonidou et al. 2007) the results showed that roses grew better in 50% almond shell with 50% pine bark mixture with a reduced irrigation regime. And following after, a mixture of 50% perlite with 50% pomace, regardless of the irrigation regime, achieved the same results.