Greenhouse production: many things to know
Dr. Mohammadbagher Lak, www.AGRIMECHANIZATION.com
Closed, controllable environment covered by transparent materials, known as “greenhouse” is a place that keeps the heat of sun radiation to let grow crops during all the seasons. Greenhouses protect the crops against sever winters and hot summers and provide them with moderate climate, always.
In greenhouse, all the climatic parameters as well as growing bed and water are controllable. Temperature, humidity, radiation, physicochemical as well as biological conditions of the soil or other growing beds and irrigation water all are controllable to provide optimum conditions for the growing plants. Moreover, controlling pests, pathogens, and weeds in closed environment of greenhouses is more feasible.
In the recent years, special attentions have been paid to development of greenhouses. Among the main reasons, followings are bolder:
– Population increases and the essentiality of more food production
– Low productivity of production in open environments regarding the seasonal limitations
– Climate change, water scarcity and the bad effect of environmental extreme temperatures on food security
– Promotion of welfare and the demand for offseason cops
– Fluctuation in food price during the year and the essentiality of balance in the prices
– Essentiality of applying high technologies towards declining the costs as well as the labor-depended issues
– Essentiality of reliable quarantine for some of plants
Types of greenhouses are defined based on their applications, shapes, covers, or the growing beds. In terms of application, there are a variety of classification: summer/winter, commercial/educational, etc. and in terms of the crop, greenhouses dedicated to grow ornamental plants vs the one for vegetables are more general (Fig. 1-1).
There are also a variety of shape in greenhouses. A-shape, gothic and cylindrical are among more conventional in Iran (Fig. 1-2) while, nylons, polycarbonate, or glass may be used as cover (Fig. 1-2). One thing important about the quality of cover is the percentage of the anti-UV content which implies the lifetime of the cover.
The growing bed in greenhouses has also various, too. In most of greenhouses soil bed is conventional (Fig. 1-3), while soil clay particles work as buffers which in turn provide conditions to neutralize the bad effect of water TDS on the plant’s growth and development. It is while, contaminations due chemical or microbial pollutants have more lifetime in the soil; thus, refining the soil needs more time and costs. Therefore, in the recent decades, a variety of soilless beds have been used in greenhouses that resulted in development of concepts of hydroponics and aeroponics (Fig. 1-3). Despite the advantages of soilless technics in controlling root diseases as well as more productive use of water and nutrients, in comparison with soil beds, the roots are more sensitive to the acidity (pH) and electrical conductivity (EC) of irrigation water/solution in soilless beds; thus, these beds need more adequate and more precise techniques.
The advantages of growing plants in greenhouse are:
– Feasibility of controlling climatic conditions
– More yields in per unit of area
– Feasibility of controlling pests, pathogens, and weeds
– Off-season production
– More productivity of water, fertilizer, and chemicals
– Feasibility of producing healthy crops
Higher performance of growing plants in greenhouses needs better knowledge of the plants biology in addition to considering the technical notes related to the greenhouse structure, facilities, and equipment.
It should be noted that costs due to cover maintenance, energy, service and repair of structure, facilities, and equipment would be added to production costs when the greenhouse is built. Thus, it is essential that the cultivation be managed based on real economic conditions to achieve the maximum profit. To achieve to this aim, selection of appropriate site, building area, the structure type and cover, the technology of equipment, type of plants, and the management system must be considered. Then, to select the crop and planning the cultivation, price elasticity of demand should be analyzed during a year and the standards as well as instructions required to produce till supply to markets must be considered. Appropriate packaging is essential to supply greenhouse products to the market. In the package, producer should consider the traceability rules governing on food markets.
2) Producing crop
As mentioned above, planning a good cultivation needs to consider the target market demands. Therefore, application of crop growth models as well as economic models can help to increase in profit margins. Sometimes, two weeks sooner or later in transplanting the crops may result in irreparable economic losses.
After considering all the aspects related to the decision made on managing the cultivation, it is necessary to prepare the growing bed. As the soil-bed greenhouses are in majority, this chapter is dedicated to soil beds cultivation considerations
2-1) Bed preparation
Bed preparation includes all the jobs must be done from remove of the last crop residues to transplanting new plants. Thus, the stages are described as below:
2-1-1) Remove of the last crop residues and weeds
The first stage is to remove all the residues remained from last cultivation and weeds which must be transferred to outside the greenhouse area. As the crops, especially in the senescence stage, are more susceptible to have pests and diseases, these residues must be obliterated.
2-1-2) Removing the obstacles
As irrigation tubes as well as other stuffs such as holders, threads, etc. may result in interruption in tillage operation, all the removable things that may considered as obstacle must be removed.
2-1-3) Spreading manure
In addition to the nutritional values, animal/poultry manure make increase in organic matter in soil which, in turn, improve the soil physical properties such as soil structure and its’ water absorption ability while the root respiration would be better in these conditions. So, it is necessary to add the manure to soil before tillage (Fig. 2-1).
The notes here are:
1) The manure must be rotten enough to avoid the import of weeds seeds or pathogens.
2) Applying manure less than needed may have not wanted results, while overuse of manure may result in other problems for the crop; thus, the optimum amount of manure added to the soil bed is recommended based on soil analysis.
2-1-4) Soil tillage
Tillage has been among the most difficult operations. Fortunately, by development of mechanization, this operation has been done by machine powers like tractors, in a variety of size (Fig. 2-2). To select the most appropriate tractor, it must be considered that the tractor has to be small in size, as much as possible to increase its’ maneuverability while its traffic has the least effect on soil compaction. Additionally, the tractor must have enough power to do the job while avoid noise and air pollution. Moreover, the tractor must be swift and low-cost to buy or rent. Ergonomics as well as safety concerns must be considered, too.
2-1-5) Bed preparation
Most of crops are grown in raised-soil-bed rows in greenhouses; thus, it is necessary to prepare the raised-soil-bed after tillage operation (Fig. 2-3). This operation may be done by labor or by special machines attached to tractors or tiller. However, it is essential to make order the rows shape manually by shovel after mechanized operation.
Good agricultural production needs appropriate cultivars, varieties, method of cultivation as well as timeliness. Thus, one must select the crop based on the season, place of growing and the market demand. Planting crops in greenhouse may include direct sowing of seeds or transplanting; however, transplanting, especially to grow vegetables, is more suggested.
Transplanting saves time and is economic (Fig. 2-4). Therefore, a grower can dedicate a part of greenhouse to produce transplants or provide them from other growers. In this stage, observance of quarantine principles is mandatory.
Sowing seeds in transplant trays may be done manual or by machines. In small scales, grower can sow the seeds by hand. But, in commercial scales, using machines are suggested (Fig. 2-5).
2-2-1) Grafting plants
Grafting plants is an approach to utilize good characteristics of both the scion and the root. In the other words, grafted plants have good properties of whether roots or shoots. Grafting the seedlings of tomatoes is a conventional operation in many countries (Fig. 2-6).
After planting the crops, generally, irrigation, crop protection, weeding, and fertilizer applications are done based on the crop requirements; however, based on crop growth and development habits, several operations such as threading, pollination, pruning leaf, suckers or fruit, or removing infected plants are done in greenhouses.
Application of fertilizer is done in two approaches: 1) mixing manure or chemical fertilizers with soil, specially before planting or top-dressing; 2) mixing chemical fertilizers with irrigation water.
To protect plants against pests or pathogens, spraying chemicals, using traps, or natural enemies are suggested.
Several greenhouses cultivated crops such as cucumbers, tomatoes, peppers, eggplants, etc. have long stems during growth and development need threading to support. The threads are hanged on wires in top of the rows, in turn, the wires are supported by bars attached to the greenhouse structure (Fig. 2-7).
Threading is possible by tying the threads to the plants; however, it is better to use clamps. But you have to care about the plant when threading (Fig. 2-8). To support long stems, using holders are suggested (Fig. 2-9).
In several plants, pollination is an essential. Especially in tomatoes, pollination has to be done after flowering. It is possible to shake the plants to spread the pollens in the air; however, in big-scale greenhouse, insects like Bumble Bees are kept to do pollination.
The other operation required to do, during the crop growth and development, is pruning the plants leaves, suckers or fruits to make the profitability of production better (Fig. 2-10).
2-4) Harvest and post-harvest
A good cultivation plan has to follow timetables resulted in harvest with the most profitability. The plan is based on the crop growth model and the target market demand. However, planning is essential, would not warranty the success in sell. Post-harvest treatments involve sorting, grading, packaging, storing and transportation have great share in the success.
3) Growing notes
Success in cultivation needs knowledge and experiences. But technical knowledge and experience are not all the things that a grower needs. Below, several notes are explained:
3-1 Quarantine principles
The best way to protect a greenhouse against parasites, is to observe the quarantine principles. So, you should:
– Have a permanent control on all the inputs including bed materials, manure, seed, seedlings entrance to the greenhouse environment
– Oblige people to observe all the quarantine principles when enter the greenhouse as well when leave.
– Use nets or other obstacles in windows to avoid the entrance of parasites (Fig. 3-1).
– Make greenhouse privacy clean to not let parasites reside there.
– Remove infected plants.
3-2) Maintenance of structure and equipment
One of greenhouse manager duties is periodic inspections and act for required services, repair, or replacement of structure (parts), equipment, and facilities (Fig. 3-2).
All the parts used in greenhouse structure, facilities and equipment have limited lifetime. To avoid risks, greenhouse managers must have a timetable for each part that contains the lifetime the required services. Moreover, it is suggested to record all the jobs done with the date of action. For example, greenhouse cover has a predicted lifetime. If the cover were not change on-time, the possibility of rupture risk would raise and result in irreparable damage. In addition, low transparency of the cover, before rupture, may result in other problems, too. Lower photosynthesis efficiency due to not proper transparency causes decline in yields.
3-2-1) Periodic services
Drip irrigation is conventional in many soil-bed greenhouses (Fig. 3-3); thus, considering the demands as well as available technologies and finally selecting proper irrigation systems is essential. However, having a proper irrigation system is one coin side, the other side is timely services based on the quality of water.
Damaged pump, filled filters, sediment settling in droppers, or ruptures in system may disturb the irrigation performance (Fig. 3-4). So, periodic inspection of irrigation system is recommended.
Heaters, fans, windows, pads, etc. must be inspected, too. Spread of CO from heaters may result in lost in cultivation performance that may even result in death of plants or people who are in the greenhouse.
3-3) Setting environmental conditions
Setting the temperature as well as humidity based on the plants requirements is important. Thus, irrigation timetable, the heating/cooling system, the duration of windows to be open/close, fans on/off, etc. must set on proper thresholds. To control the equipment, greenhouse owners need adequate and precise sensors.
The control systems range a simple timer or thermostat to high-tech systems working with crop growth models. So, selection an appropriate control system needs owners to make comprehensive decisions based on their needs, potential and the economic considerations (Fig. 3-5).
3-4) Skill to work with equipment
Greenhouse managers as well as technical personnel are expected to have technical skills to work with equipment and facilities. They are supposed to be aware of the principles of service, maintenance, and repair of structure, facilities, and equipment, too. On the other hand, spares, and consumables such as bolts, nuts, nails, rivets, wires, and fittings for the irrigation system as well as tools to work with them must be available in a place like warehouse or workshop near to greenhouse privacy that are delivered only to authorized personnel.
3-5) Observance of safety principles
Personnel falling or slipping, drowning in a water tank, poisoning by pesticides or fertilizers, exposure to acids (to moderate the water pH or etc.), suffocation due to vapor defects, insect bites, electrocution, fire burning, etc. are always close to occur in greenhouses. Therefore, the greenhouse manager must take action to observe all aspects of safety and risk prevention and provide tools and measures to combat the risks.
3-6) Observance of occupational health
Periodic washing of clothes and keeping workwear clean, assigning suits, gloves, hats and glasses for special tasks such as spraying, using clothes with insect repellent colors, observing the principles of ergonomics in working with tools, providing a resting room for workers and observing quarantine issues, are health tips that must be observed.
3-7) Observance of environmental issues
Observing the timeliness, turns and permitted dosing of fertilizers and pesticides according to soil deficit and plant protection recommendations and preventing the accumulation of more pesticides than the permitted amounts are among the environmental issues that the greenhouse manager should consider. Preventing the spread of weeds, pests and pathogens in greenhouses and the surrounding areas by proper quarantine and eradication of infected plants as soon as possible are among the environmental issues, too.
3-8) Economic analysis
Before cultivation, all the detailed costs must be estimated and analyzed. In the analysis, all the fix as well as variable costs need to be considered. Additionally, an estimation of the yield and the product price needed to predict the potential profit. Moreover, the approaches resulted in direct deliver to the end user should be considered.
To achieve the highest benefit, greenhouse owners, need a team of specialists in the fields related to crop production, technology application, market investigation and modelling.
4) Agricultural systems analysis
Agriculture is a complex system consisted of subsystems involving product, resources, environment, and capital which are provided by human to meet human needs.
In the system, human plays role as both producer and consumer, while the management of system is the human duty, especially in the greenhouse. However, there are always limitations that take the process out of the manager’s hands, and under conditions, resulted in inevitable failure.
Proper understanding of the subsystems and elements forming agricultural system, can provide manager with this opportunity to produce qualified healthy crops, in sufficient quantity with highest productivity of resources, capital and environmental conditions that may result in good profit if marketing principles are followed. Thus, a successful greenhouse manager, needs to know processes models as well as systems analysis in addition to technical knowledge, marketing principles, and production management.
Model development and systems analysis are high-level skills that need higher academic degrees; therefore, producers must ask experts to give them advice.
4-1) Model development
To analyze agricultural systems, mathematic models are used, often. Development of mathematic equations to simulate crops growth procedures resulted in development of various crop growth models to predict the reaction of crops to environment. These models are increasingly used to help agricultural development.
Last progresses in continuously automated monitoring of crops behavior, gave us this opportunity to relate the crop growth state to the environmental conditions always.
Models are typically as bellow:
4-1-1) Experimental Models
Experimental models explain the system behavior, simply. In these models, experimental data are used to fit mathematic equations. These models need big data and are able to explain the system behavior in the range of measured data. In the other words, experimental models representing only a scheme of the current conditions and are not able to predict or recommend while no information is extractable to explain the mechanisms.
4-1-2) Mechanistic models
These process-oriented models quantitatively describe the mechanisms and processes that guide system behavior. In order to create a mechanistic model, the analyzed system, its processes and mechanisms are quantified separately and then by combining them, the relevant system model is presented. Predicting and estimating the effect of stress is one of the features of these models.
A process-oriented model of plant growth calculates rate variables (photosynthesis rate, leaf area expansion rate, etc.) and state variables (plant biomass, yield, etc.) and quantifies processes as a function of environmental factors, such as light and ambient temperature. In this method, the growth rate at each stage of plant development during the growing season can be calculated based on the condition of the crop, soil, and climate (Fig. 4-1).
4-2) Models’ application
Plant growth models are increasingly used in analysis of agricultural systems and simulate the plant’s response to growth factors by using mathematical equations. Crop growth models can be used in yield estimation, agricultural planning, farm management, climatology, and agricultural meteorology.
4-3) system analysis
In order to analyze agricultural systems, it is necessary to first identify the system, subsystems and components; then, the role and relationships between the components must analyzed; and finally, the desired purpose has to be defined. The strengths and weaknesses of the system as well as the opportunities and threats of the environment (SWOT) be identified and the necessary strategies to increase its productivity be developed. As well, they need sometimes using only the first few principal components among many and ignore the rest. Thus, Principal Component Analysis (PCA) is the process of computing the principal components and using them to perform a change of basis on the data.
To analyze the systems governing on a greenhouse, one must consider sets of solid parts, machines, and electrical/electronic tools as well as growth bed, plants, pesticides, fertilizers, and the management manner which are placed in an environment with special geographic and climatic conditions that produces crops using time, energy, and money. This product must result in income to provide human benefit. So, to manage a greenhouse, one needs recognition all the above.
Joint teams of system analyzers in collaboration with engineers, crop growth modelers, as well as market analyzers are needed to form, if a greenhouse manager aims to optimize their performance.
4-3-1) Multi criteria decision making
Many of parameters affecting on the performance of a greenhouse manager. Managing teams are suggested to get familiar with multi-criteria decision making (MCDM) to consider the weight of each criterion of decision making based on its’ importance. Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) as well as Analytic Hierarchy Process (AHP) are among MCDMs appliable in agricultural systems analysis.