DR. S. M. ALAM
Mar 14 - 20, 2011
Spinach is an edible flowering plant native to central and southwestern Asia. It is an annual vegetable, which grows to a height of up to 30 cm. Spinach may survive over winter in temperate regions. The leaves are alternate, simple, ovate, to triangular-based, very variable in size from about 2-30 cm long and 1-15 cm broad, with larger leaves at the base of the plant and small leaves higher on the flowering stem.
The flowers are inconspicuous, yellow-green, 3-4 mm diameter, maturing into a small, hard, dry, lumpy fruit cluster 5-10 mm across containing several seeds.
Spinach is thought to have originated in ancient Persia (modern Iran). Arab traders carried spinach into India, and then the plant was introduced into ancient China, where it was known as "Persian vegetable". The earliest available record of the spinach plant was recorded in Chinese, stating that it was introduced into China via Nepal (probably in 647 AD). In AD 827, the Saracens introduced spinach to Sicily. The first written evidence of spinach in the Mediterranean are in three tenth-century works, the medical work by al-Razi (known as Rhazes in the West) and in two agricultural treatises, one by Ibn Wahshiya and the other by Qustus al-Rum.
Spinach is an excellent source of beta carotene, vitamin C, E, and K, potassium, iron, sulphur, sodium, folic acid and oxalic acid. It contains more protein than most vegetables. Spinach is one of the vegetables with the highest amount of chlorophyll, a fat-soluble substance that stimulates hemoglobin and red blood cell production. Chlorophyll is known to have a chemical formula remarkably similar to that of hemoglobin and it is said that the ingestion of chlorophyll will raise hemoglobin in blood without increasing the formed elements.
In animals, hemoglobin carries oxygen as food to cells and exchanges it for carbon dioxide which is then discharged as waste from the system. So plants like spinach that are high in chlorophyll support the liver in detoxifying and cleansing the blood. With spinach, the effect is reinforced by its considerable amount of sulphur. Sulfur is an acid-forming mineral that protects the protoplasm of the cells, disinfects the blood and helps body resist bacteria. Folic acid is needed to form red blood cells and support the formation and function of white blood cells.
Spinach, along with other green leafy vegetables is considered to be a rich source of iron. For example, the United States Department of Agriculture states that a 180 g serving of boiled spinach contains 6.43 mg of iron, whereas one 170 g ground hamburger patty contains at most 4.42 mg. The larger portion of dietary iron is absorbed slowly in its many food sources, including spinach. This absorption may vary widely depending on the presence of binders such as fiber or enhancers, such as vitamin C. Spinach contains iron absorption inhibiting substances, including high levels of oxalate, which can bind to the iron to form ferrous oxalate, which renders much of the iron in spinach unusable by the body. In addition to preventing absorption and use, high levels of oxalates remove iron from the body. But, some studies have found that the addition of oxalic acid to the diet may improve iron absorption in rats over a diet with spinach without additional oxalic acid. Spinach also has a high calcium content. However, the oxalate content in spinach also binds with calcium, decreasing its absorption. Calcium and zinc also limit iron absorption.
The exceptionally high antioxidant property of spinach is due to carotenoids, beta carotene and lutein, which are three to four times higher than in broccoli, for example. These naturally occurring fat-soluble pigments are most effective when eaten with some fat. Spinach also has plenty of potassium, which supports a healthy nervous system, aids proper muscle contraction, stabilizes blood pressure, regulates the transfer of nutrients through cell membranes and, together with sodium, controls the water balance of the body.
When eaten in large amounts, spinach could damage already impaired kidneys: oxalic acid removes calcium from the blood in the form of calcium oxalate, and calcium oxalate obstructs the kidney tubules.
Spinach has a high nutritional value and is extremely rich in antioxidants, especially when fresh, steamed, or quickly boiled. It is a rich source of vitamin A (and especially high in lutein), vitamin C, vitamin E, vitamin K, magnesium, manganese, folate, betaine, iron, vitamin B2, calcium, potassium, vitamin B6, folic acid, copper, protein, phosphorus, zinc, niacin, selenium and omega-3 fatty acids.
Polyglutamyl folate (Vitamin B9 or folic acid) is a vital constituent of cells and spinach is a good source of folic acid. Boiling spinach can more than halve the level of folate left in the spinach, but microwaving does not affect folate content.
This is an important vegetable of winter season and requires a cool and moist climate. Low temperature and high humidity helps in the development of succulent, tenders mild flavored foliage and quick growth. The plant prefers sunshine. For seed development and maturity, plant requires long and warm days. Spinach germinates best at soil temperature below 10-12oC. At high temperature, the seed fails to germinate because they enter into a dormant state, which continues until the temperature again falls below 10-12oc. Spinach can be grown successfully on a variety of soils, but a fertile sandy loam high in organic matter is preferred. The use of cover crops and green manure crops is recommended to maintain the soil organic matter. The soil pH should range between 6.4 to 6.8. Spinach is very sensitive to acid soils, thus a soil test prior to planting this crop should be made. Low germination, yellowing and browning of margins and tips of seedling leaves, browning of roots, general slow growth and even death of plants, may indicate that the soil is too acid. If the pH is too high, leaves may have a yellow color referred to as chlorosis.
A well-prepared seedbed that is free of large clods permits precision planting with rapid and uniform emergence of spinach seedlings. Uniform depth of seeding is critical when using pre-plant-incorporated herbicides because if spinach seeds are planted too deeply, seedlings may be killed by herbicide. Well-prepared seedbeds also permit proper and accurate incorporation of pre-plant-incorporated herbicides, leading to improved weed control and reduced phytotoxicity to seedlings. In situations where cultivation can be used, uniform beds with level bed tops are essential. Spinach requires abundant moisture to insure a high quality product. An application of one inch of water every seven to ten days, when rainfall is inadequate, is recommended. Keep soil moist until seedlings have emerged.
There are two varieties of spinach in Pakistan: local Sindhi and prickly heat. Seeds are broadcasted on the flat beds or in ridges and are mixed with fully prepared soil and pressed with some hard material immediately after sowing seed, irrigation water is applied. Spinach requires a high level of fertility, especially nitrogen. Per acre requirements on sands and sandy loams are 85 to 120 lb N; 75 to 85 lb P2O5; and 85 to 150 lb K2O. On heavier clay soils, 50 lb/acre of each nutrient should be adequate. Fertilizer is often broadcast and worked into the soil prior to seeding. If the fertilizer is banded at seeding, it should be placed along each side of the rows 2 to 3 inches below the level of the seed.
A healthy, vigorous crop provides substantial competition that suppresses weed growth and acts as part of the weed control program. Therefore, proper fertilization, irrigation, and insect and disease control measures promote good crop growth and compliment other weed control measures. Ideally, good cultural practices and careful use of herbicides will result in minimal hand-weeding requirements. After planting the crop, there are two periods in which herbicides may need to be applied, depending on the weed species.
The crop is ready for cutting with in six to eight weeks after sowing. The cutting is done 2 cm above the ground level when plants have put five to six leaves. New foliage is cut later with three to four cuttings. Spinach is sold loose, in pre-packaged bags, or frozen. Fresh spinach loses much of its nutritional value with storage of more than a few days. While refrigeration slows this effect to about eight days, spinach will lose most of its folate and carotenoid content, so for longer storage it is frozen, cooked and frozen, or canned. Storage in the freezer can be for up to eight months.