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In modern age, the population of world is increasing abruptly. In 1999 a survey was conducted which showed that human population in the world is above six billion and is continuously growing at the rate of 80 million per year (Anonymous, 2008). This population explosion is occurring mainly in the poorest parts of the world. According to an estimate by 2015, there will be more than 10 million inhabitants in only 23 countries alone and out of these 23 countries 19 will be of developing countries. Pakistan also comes in the list of developing countries. Pakistan estimated population in 2010 was over 170 million (Population Census Organization, 2010), making it among world top ten most populous countries. Food consumption of a country is mainly controlled by population and income. According to another survey it was observed that world food demand is growing @ 2% per year out of which 1.8% is due to population and only 0.2% was due to rising income of citizens (Anonymous, 2008). From this statistics it is pretty clear that population is has direct and major influence on food demand. In With the increase in population, food demand of a country also increases. In case of overpopulation the per capita food consumption is decreased because of less availability of food resources. For a healthy nutritional diet WHO recommends 400 grams of vegetable intake / capita/ day. However, in Pakistan average vegetable consumption is only 82.21 g/ capita/ day (FAO, 2007). The reason of this low food consumption is neither the fertility level of our soils nor the area of cultivation. Perhaps actual reason is population outburst followed by lack of awareness among Pakistani people regarding the importance of vegetables in healthy diet. Until now wheat has fulfilled our food requirements but if the population of Pakistan continues to increase with the same pace there is no doubt that in future it will be very difficult to feed whole population properly. Although until know as the population has increased we also adopt new ways (like use of hybrid varieties, advanced cultivation practices etc.) to increase the yield of our agronomic crops. But as everything has so limits beyond which we cannot go. If currently we are obtaining average 25-30 tonnes per acre yield in future when we need 3-4 times more food how we can get 75-100 tonnes. Moreover, all the agronomic crops require more area for cultivation and we all know that the cultivated area is continuously decreasing as the population increases. In such circumstances vegetables can provide a good food source. They require less space. Moreover, the maturity time of vegetable is also shorter than agronomic crops. Vegetables can provide a cheap source of vitamins and minerals and can easily compete with agronomic crops on nutritional basis.
God has gifted Pakistan with diverse climate and fertile land. In Pakistan 27% of total area is under crop cultivation out of which 80% is irrigated area. Pakistan has one of the highest proportions of irrigate area in the world. Varying climatic conditions of Pakistan offers cultivation of numerous vegetables. At present, according to an estimate vegetables account for 12.4 percent of the value-added in overall agriculture of Pakistan. The trend of home or kitchen gardening is also becoming popular. Vegetables grown in Pakistan can be categorized as winter and summer vegetables. Winter vegetables include all root, tuber, bulb and leafy vegetables while summer vegetables are mainly from cucurbitaceae family.
The cucurbitaceae is a very huge family of about 125 genera including 960 species. Most of the plants in this family are annual vines but there are also woody lianas, thorny shrubs, and trees (Dendrosicyos). Many species have large, yellow or white flowers. The stems are hairy and pentangular. Tendrils are present at 90o to the leaf petioles at nodes. The flowers are unisexual, with male and female flowers either on different plants or on the same plant. The female flowers have inferior ovaries. The family cucurbitaceae contains many delicious vegetables among them bottle gourd is a compelling vegetables crop. Bottle gourd is important because of its various health benefits. White pulp of fruit is cooling, emetic, purgative, diuretic and antibilious. Oil from the seeds is cooling and used to relieve headache. Seeds are nutritive and diuretic. Decoction of leaves mixed with sugar given in jaundice. Fruit is used in cholera (Vashista, 1974). However, bitterness in cucurbits is due to a complex compound Cucurbitacin (tetracyclic triterpenoid) which is found responsible for cytotoxic effect in humans which results in hepatic and pancreatic dysfunction (Sharma et al. 2006).
The genus Lagenaria has six species. Bottle gourd (Lagnaria siceraria) also belongs to this family. Bottle gourd is believed to be the indigenous to the tropical lowlands of Africa, south of the equator. Archeological evidences indicate that it existed in old and new world more than 12000 years ago. Its dry shell has been traditionally used as utensils and handicraft items in many parts of the world. Bottle gourd is an annual, vigorous, climbing or running vine with large leaves. It is a very fast growing plant and starts flowering just 2 months after seeding. The stem of bottle gourd is furrowed longitudinally. The vine has tendrils along the stem. The foliage has soft hairs in it. The leaves are large almost 15 inches wide, circular in shape, with smooth margins. The flowers are produced singly on the leaf axil. The male flowers have long peduncle as compared to females. The flower colour is white. Anthers are produced on short filaments which are grouped together at the centre of flower. The flower stigma is branched and short. There are many seeds in single fruit embedded in the white flesh of the fruit. On over ripening the skin colour of fruit is turned into brown and it also hardened like a wood. The flesh inside the fruit is also shriveled. On shaking the fruit a clear clanking sound of seeds can be heard. Normally the fruit is harvested fresh at green stage but for seed production the fruits are allowed to over mature.
In 2008, average yield of bottle gourd in Pakistan was 9 tonnes/ hectare while in developed countries like china yield was much higher i.e. 19 tonnes/ hectare (FAO, 2008). There are many reasons of this low yield in Pakistan. Use of poor quality vegetable seeds, improper irrigation and fertilizer application are most important factors responsible for low yield of crop. In plants, two elements potassium and nitrogen are required in greatest amounts, while in animals potassium is the third most abundant element, after calcium and phosphorus. Potassium helps plants to resist drought and effects from excessive temperatures. It also increases crop resistance to disease. Potassium aids plants in the production of starches, controls root growth, and regulates the opening and closing of stomata which is important for efficient water use.
The letter K, used to symbolize potassium, comes from the German word kalium. During Colonial times, people burned wood and other organic matter in pots to manufacture soap. The ashes were rinsed and the water was allowed to evaporate, leaving a residue of potassium salts. People called the residue "pot ashes" or potash. These salts were boiled with animal fat to produce soap. In 1868, Samuel William Jackson, a botanist in Connecticut, burned plants and analyzed the ash. Jackson found plants consisted of large amounts of potassium, as well as other minerals. His work led to the use of fertilizers to promote an increase in crop yields. In modern age potassium demand of the world is very high. Canada leads the world potash production and exports, producing 8 million tons in 2008. Russia, Belarus and Germany are also top producers of potash. China is the world's leading potash consumer, using nearly 8 million tons in 2008.
There is no doubt that potassium is abundant in nature, comprising about 2.4 percent of earth crust. The feldspar and mica are the biggest potassium sources in earth crust. But here a question arises that if potassium is so abundant then why to apply potassium? The potassium present in nature is mostly in the form which plants cannot uptake. Moreover potassium uptake also varies from soil to soil. Potassium uptake is most rapid on warm, moist soils that are well aerated and have a slightly acidic to neutral pH. As soil temperature increases, plant metabolic activity increases which increases root growth and root activity. Warmer soil temperatures also increase the diffusion rate of potassium in the soil solution which increases potassium uptake by the root system. Excess soil moisture can lower soil oxygen levels which in turn decrease the respiration rate for the plants root system and thus lowers potassium uptake. Also, excess water can increase the amount of leaching of potassium, particularly in sandy soils. In alkaline soils, increased levels of other cations such as calcium, potassium and sodium can affect the availability of potassium in the soil. The calcium and magnesium cations can displace the potassium from the exchange sites on the clay particles and sodium competes with potassium for uptake by the plants root system. Therefore many soils lack sufficient quantities of available potassium for satisfactory yield and quality of crop. For this reason available soil potassium levels are commonly supplemented by potash fertilization to improve the potassium nutrition of plants, particularly for sustaining production of high yielding crop species and varieties in modern agricultural systems. Thus, potash, the fertilizer trade term referring to fertilizer materials containing potassium, has become an increasingly important input for satisfying demands of an expanding population for food, fiber and other commodities. Approximately 95 % of current global consumption of potassium is used for fertilizers; the remainder is used in various industrial applications including the manufacture of caustic potassium and other intermediate chemicals. Potassium chloride or muriate of potash (MOP) is the most popular potassium fertilizer. Potassium sulphate (SOP) is the next most important potassium source followed by potassium magnesium sulphate, potassium nitrate, potassium phosphate, and solutions of potassium thiosulphate and potassium polysulphide. Other potassium containing salts such as potassium carbonate, potassium bicarbonate, and potassium hydroxide have limited use for the production of high-purity fertilizers for foliar application and other specialty uses.
Potassium can be applied by different methods like side dressing, foliar application and via fertigation. Each method has its own advantages and disadvantages. Mostly potassium side dressing is done at the time of seed bed preparation and SOP is most commonly used for that purpose. Recently foliar application method is becoming more popular because in this method salts are available to plants easily. In Foliar application method different water soluble potassium salts are sprayed on leaves at regular intervals. Most commonly used salts for foliar application are KNO3, K2SO4 and KCl. Their effectiveness varies from crop to crop for example in spinach KH2PO4 (Cengiz et al., 2001), in Jute KNO3 (Anwarul-Islam et al., 2003) was found effective. In bottle gourd KNO3 was successfully used to induce tolerance against salinity (Ahmad and Jabeen, 2005). In a number of studies involving several fruiting crops (e.g. cucumber, mango and muskmelon) where soil-applied fertilizer K was compared to foliar K applications, the latter approach consistently resulted in improved fruit quality attributes whereas the former approach generally had little or no effects (Demiral and Koseoglu, 2005; Lester et al., 2005; Lester et al., 2006; Jifon and Lester, 2009). From above facts it is clear that potassium has a significant role in improving quality of perishable produce. But is there any role of potassium foliar spray in improving bottle gourd fruit as well as seed quality?