During the last decades the area of crops grown indoors i.e. cucumber, tomato and sweet paper has been expanded rapidly near the big cities of Punjab. Environment of the Punjab allow using many simple plastic tunnels for successful indoor vegetables production. Tunnels can be installed in the area where the average temperature does not get lower than 10°C during the coldest months of December and January. At this temperature growth of the crops is slow but it is resumed with the onset of spring. In the areas where the lower average temperature is < 10°C, economic indoor vegetable production is hardly visible without additional heating in these months, and planting may have to be postponed till early spring.
For indoor cultivation of vegetables, many construction and covering materials are available ranging from simple tunnels covered with plastic to still-constructed greenhouses covered with glass and computer-controlled environmental conditioning. However, the latter requires a heavy capital investment while the plastic tunnels are relatively cheap and these suit quite well for the purpose of over bridging the gap in the vegetable market during the cold months or to be earlier in the market than the produce of the open fields.
The disadvantage of the plastic tunnels is that the environmental conditions for an optimum growth of the plants, temperature, relative humidity and gaseous exchange i.e. CO2 & O2 cannot be regulated. The temperature depends on the radiation, and the relative humidity depends on the temperature.
During the period of cold (cloudy or foggy) weather, the leaves of plants do remains wet over a longer period and a relative high amount of fungicides with different formulations have to be used to avoid infection of various possible diseases.
Further more in areas where vegetable crops do succeed in winter period, it will be practically impossible to produce vegetables under plastic cover in summer time without additional shading, cooling and/or other protective measures.
Cucumber performs best on sandy loam with a pH of 6.5-7.5, whereas tomatoes and sweet pepper on a light, free draining, and fertile loam with a pH of 5-7. It may be mentioned that all the three crops can perform quite well on other type of soils as well. Soi management is important in this regard. As we see on the following pages, we can influence it by managing its humus and fertilizers contents, particle size, and soil borne diseases.
ii) ORGANIC MATTER:
In Punjab there is very hot and dry climate. Soils are very low in organic matter content. The added organic matter quickly disappears from the soil under influence to the high soil temperature which encourages bacterial activities that do break down the organic matter rapidly. It is therefore necessary to replace the organic contents of the soil by adding manure or if available other types of organic matter.
On sandy soils, the incorporation of organic matter increases the water holding capacity, and on heavy soils it increases the porosity and gives greater aeration. Preferably only well-decomposed manure or other organic matter should be used, otherwise nitrogen deficiency may occur.
Relatively large amounts can be given without any harm, but remember that it is not possible to make a larger increase in the organic matter content of the soil on permanent basis.
Commercial fertilizers are added to the soil with the particular purpose of directly increasing the amount nutrients available for the plants to secure a high yield of good quality.
Between these three vegetable crops, there is a variation in the need of fertilizers. Quantity & requirement of a particular fertilizer depend to a great extent on the fertility of the soil.
To assess and maintain the nutritional status of a crop, there are some tools to assist. Mostly soils in the Punjab are basic in nature. So the acidic fertilizers should be used along with addition of Gypsum to get good results. The following tools are being used for these purposes.
a) Standard fertilization as per general recommendation of the Research Station in the region should be applied.
b) Plant observation from reliable method.
c) Tissue analysis is a quite sophisticated method but not easily understandable by growers.
d) Indications of “Hidden Hunger” of plant.
Results are affected by many factors, most reliable is the soil analysis.
iv) SOIL ANALYSIS:
This tool gives a fair idea about the level of available nitrogen, phosphorus and potash the main mineral requirements of plants and also of magnesium, calcium and other minerals if required. pH and EC measurements can be known by this way.
The laboratory (where the samples are sent and tested) will supply the grower with an analysis report and indication whether the nutrient levels are low, good or high and what rate and kind of fertilizers should be given for a certain crop.
Regarding the pH, this indicates the degree of acidity or alkalinity of the soil and is expressed in a number. A pH of 7 in neutral, below is acidic and above is alkaline. Bacterial activity and the availability of nutrients in the soil are best when soil is at pH range between 6-7.5. Cucumber, tomatoes and sweet pepper will grow successfully within this range. Low pH can be increased by liming and high pH character of soil can be overcome by the use of acid farming fertilizers such as ammonium sulphate or ammonium nitrate for nitrogen, single super phosphate for phosphorus and sulphate of potash for potash.
Plant roots in soils with high salt content will extract less easily from the soil solution. Visual symptoms of salt injury are a lot like those of moisture stress i.e. the leaves wilt and eventually turn brown especially along the edges. Also the roots will turn brown and die. In soil with a moderately high salt concentration, growth may be reduced and the plants become stunted. Often seed germination is poor when salts are high and the young seedling leaves may be chlorotic.
NOTE: One EC is more or less equivalent to 650 ppm of salt.
When taking a soil sample, make sure that it will be a representative of whole area.
v) APPLICATION OF FERTILIZER:
Phosphate should be given prior to planting, because the plants do need it in young stage of growth. Furthermore, phosphate moves little from the place it is put, therefore it should be well incorporated into the soil, so that it may be available in the root zone for a long time.
Where phosphate fixation does occur (Phosphate combine with Calcium under alkaline conditions and with Aluminum and Fe in acidic soil), the Fertilizer may be placed in bands near the plants at planting time.
Regarding good quality of soil, fertilizing with potash is in general most considered. Nevertheless a shortage may occur if soil analyses indicate a shortage, incorporate the potash fertilizer prior to planting in the same way as phosphorus. Nitrogen is often given to the plant at different intervals, part of it as a top dressing prior to planting together with phosphate and potash.
Due to the fact that most tunnels do use irrigation systems either furrow or drip irrigation, so it is easily manageable to supply fertilizers at each watering. A new word for this is fertigation (combination of fertilization and irrigation). The theory behind the fertigation is that the plants need for water and fertilizer are almost parallel. As more sunlight is received, the more water and fertilizer are needed. While under cold circumstances, little of both are needed.
It is important to remember that when fertilizer is applied with watering, it must be done thoroughly; if the watering is light, soluble salts quickly accumulate causing severe checks in growth. It may be advisable to alternate between clean water applications and dilute fertilizer solution.
One of the most important requirements for good vegetable cultivation under plastic tunnels is to maintain sufficient moisture in the soil. Frequency and amount of water be given on each irrigation, depends on:
a) Soil type
b) Rooting depth of the vegetable crop
c) Weather conditions
d) Plant development
Heavy soils and those with plenty of organic matter will require less frequent watering than light well-drained sandy soils.
Shallow rooted vegetables require more frequent irrigations than deeper rooted vegetables.
Tomatoes are regarded as rather deep rooted with more than 120cm root penetration, while cucumber and sweet pepper with 90-120cm. In this respect, it is advisable that once transplants show the first growth, keep them a bit short of water to enable them to go deep with their roots.
Plant under hot and dry conditions, plants lose more moisture into the air than in cooler and more humid areas due to more evapo-transpiration rates. Under these conditions, the soil has to be irrigated adequately and regularly. However when the weather conditions become rather cold, watering should be Slowed down drastically.
Young plants under warm weather conditions may benefit more from small quantities of water at regular intervals.
More mature plants utilize and evaporate more water in later stages of growth when leaf size and leaf area is larger. There are different ways for determining when and how much water to give, but the least reliable methods are:
a) Scheduled irrigations by calendar but this system do not tell anything about the moisture level of the soil.
b) Following other growers system: borrowing good ideas from successful growers is to be recommended, but irrigation schedules are not recommended. Since soils, plant development etc. might be different.
c) Checking on plant appearance.
d) Waiting till the plants shows signs of moisture stress results in too late irrigation and an optimum crop yield cannot be realized any more.
e) More advisable or actually it should be must for every grower is to carry out regular spot checks with a shovel or soil tube. By squeezing and balling the soil, a rough idea about the moisture may be taken.
f) Sandy loam soils apparently show the sign of desiccation on upper layer due to rapid absorption of water to under lying layers.
About Author: Sajid Iqbal Sandhu is CEO of The Green Circle Pakistan (Innovative Agriculture Technologies). Besides this, he is a Tunnel Expert, Importer, Distributor, Seed Acclimitizer, Agri Consultant and Freelance writer. Email: firstname.lastname@example.org
Copyright Hortist, 2013