Potato crop under nutrition

Origion of potato

The potato, an important world crop, is a single species, Solanum tuberosum belonging to plant family solanaceae. Is one of the four major food crops of the world. The other three crops being rice, wheat and maize. Other well known crops in that family are tomato, egg plant, various species of chili peppers and tobacco.

     Potato as a food crop probably originated in the Andes Mountains of South America and from there spread into Europe and into the rest of the world (Hawkers, 1990).

     Potato was first introduced to Sudan in the late thirties of this century by two merchants (Manoli, a’ Greek and Abd El-Hadi, an Egyption). They used to distribute unknown potato seed tubers, introduced from Egypt, to farmers of El-Sheheinab and El Geili areas, 45 km north of Khartoum to be grown there. They used to purchase the harvested produce and sell it to the Europe communities in Khartoum and export the rest to Egypt (El-Hassan, 1989).

     Others reported that potato was first introduced into Sudan by the British in the early years of the third decade of previous century, (Abdalla and El-Shafie, 1983).

Importance and food value:

     Potato produces more dry matter food, has well balanced protein and produces more calories from unit area of land and time than other major food crops.It is a nutritious food containing practically all the essential dietary constituents. Like cereals, carbohydrates are the major constituents of potato. Besides, it contains essential nutrients such as proteins and minerals like calcium, phosphorus and iron, and vitamins (B1, B2, B6 and C). Each 100 grams of potato tuber contains 79.8 grams of water, 2.5 grams proteins and 17.1 grams carbohydrates (Watt and Meril, 1963).

Potato production in the world

     Among the major potato growing countries of the world, China ranks first in area, followed by the Russian Federation, Ukarine and Poland.India ranks fourth in area in the world. The present area under potato in India is about 1.4 million hectares. India produces a total of about 25-28 million tones of potatoes every year and ranks fifth in production, each hectare produces about 16-19 tonnes of potatoes however European and American countries have produces about 30-40 tonnes per hectare (pandey, 2007).

Potato production in Sudan

Potato in the Sudan gained popularity specially during the 1980’s and 1990’s. Khartoum state represents the main area for potato production and consumption in Sudan. The areas under potato in Khartoum state has been estimated at about 8500 and 18045 feddan on average by 1991 and 2010 respectively. It produces about 80% of Sudan’s total production. The major areas of cultivation in Khartoum state are concentrated in the northern part along the western and eastern banks of the Nile. (El-Amin, 1993 and Agric.report, 2010). Other production areas that are of regional importance are areas around Shendi and Atbara in River Nile state, Jebel Marra area in Darfur, Gilo in southern Sudan, Kassala in easternSudan and some other new areas of introduction in Gezira state. (Geneif and Sadik 1989).

The Importance of Nitrogen in Agriculture

      Nitrogen (N) is widely distributed throughout the lithosphere, atmosphere,

hydrosphere and biosphere. In contrast to the other two major plant nutrients,

phosphorus (P) and potassium (K), rock deposits of N in the lithosphere do

not exist, and therefore fertilizer N is made from the conversion of unreactive

atmospheric dinitrogen (N2) to reactive forms of N. It is striking that only a

very small part of this N is present in the soil (approximately the first meter of

the earth crust), mostly as organic forms. The total N content of surface

mineral soils normally ranges between 0.05 and 0.2 per cent, corresponding to

approximately 1750 to 7000 kg N ha-1 in the plough layer. Lower as well as

higher amounts can be found, depending on the various soil-forming

processes. Of this total N content only a small proportion, in most cases less

than five per cent, is directly available to plants, mainly as nitrate N (NO3--N)

and ammonium N (NH4+-N). Organic N, being the rest, gradually becomes

available through mineralization.

Nitrogen is the most important plant nutrient for crop production. It is a

constituent of the building blocks of almost all plant structures. It is an

essential component of chlorophyll, enzymes, proteins, etc. Nitrogen occupies

a unique position as a plant nutrient because rather high amounts are required

compared to the other essential nutrients. It stimulates root growth and crop

development as well as uptake of the other nutrients. Therefore, plants, except

legumes which fix N2 from the atmosphere, usually respond quickly to N applications.

In most ecosystems, N moves from the soil to the plant and from the plant

(Residue) back to the soil through the microbial biomass. It undergoes many

transformations, which are all included in the “nitrogen cycle.” In natural

ecosystems, this cycle is more or less closed, i.e. N inputs are in equilibrium

with N losses. In agricultural ecosystems, however, this cycle is disturbed by the

export of substantial amounts of N with harvested products. As a consequence,

the use of N fertilizers has been essential to keep and/or increase the

productivity of the soil. In the past 50 years, increased fertilizer N use and

better N management were the major contributors to large increases in global

food production (Smil, 2001).

Role of Nitrogen in Plants

Plants are surrounded by the nitrogen (N) in our atmosphere. Every acre of the earth’s surface is covered by thousands of pounds of this essential nutrient, but because atmospheric gaseous nitrogen is present as almost inert nitrogen (N2) molecules, this nitrogen is not directly available to the plants that need it to grow,

develop and reproduce. Despite nitrogen being one of the most abundant

elements on earth, nitrogen deficiency is probably the most common nutritional problem affecting plants worldwide. Healthy plants often contain 3- 4% nitrogen in their above ground tissues. These are much higher concentrations than those of any other nutrient except carbon, hydrogen and oxygen, nutrients not of soil fertility management concern in most situations. Nitrogen is an important component of many important structural, genetic and metabolic compounds in

plant cells. It is a major component of chlorophyll, the compound by which plants use sunlight energy to produce sugars from water and carbon dioxide (i.e. photosynthesis). It is also a major component of amino acids which, the building blocks of proteins (Gilbert 1949, Tisdale and Nelson 1956). Some proteins act as structural units in plant cells while others act as enzymes, making possible many of the biochemical reactions on which life is based on. Nitrogen is a component of energy-transfer compounds, such as ATP (adenosine triphosphate) which allows cells to conserve and use the energy released in metabolism. Finally, nitrogen is a significant component of nucleic acids such as DNA, the genetic material that allows cells (and eventually whole plants) to grow and reproduce.

Role of nitrogen in crop production

The role of nitrogen fertilizers in crop production is well documented (Samuell et al. 1985). At certain nitrogen levels, the increase of nitrogen can increase the yield significantly at sufficient soil moisture content (Viets, 1962; Olson et al. 1964b). Regarding this, Follet et al. (1981) discussed the role of nitrogen in plant nutrition and mentioned that nitrogen element is often deficient in the soil. These authors confirmed the important role of nitrogen in plant nutrition due to its strong relation with the strength of the vegetative growth and the formation of the dark green coloure in the leaves of the plant.

     The bulk of soil nitrogen is in the organic form, which is unavailable to the plant. This becomes available through biochemical process of mineralization, which converts organic nitrogen to inorganic form (Follet, 1981). However, nitrogen is required by the plant in large quantities, it is one of the major component of amino acids, proteins, nucleic acid, amines and amides. Therefore, the supply of nitrogen to plant is vital when both quantity and quality are considered. This was supported by the findings of (Westermann and kleinkopf 1985, Westermann et al. 1988), who reported adequate nitrogen fertilization is critical for optimizing potato yield and quality, and insuffient available nitrogen leads to reduce growth, reduce light interception, limited yield and early crop senescence. On the other hand, excessive available nitrogen can result in reduce yield, delayed tuber set and reduced tuber dry matter content (kleinkopf et al.1981). Thomas et al. (1978) who reported asignificant increase in yield and seed protein on the addition of nitrogen fertilizers to wheat. Similarly, Robinson (1977) recorded appositive correlation between the levels of soil nitrogen and seed proteins content.

     Crop nitrogen demand is the product of the expected yield and the internal nitrogen requirement, which can be thought of as the minimum amount of plant nitrogen associated with maximum yield (Standford and Legg 1984). Although yield levels varied for the two seasons, Bowen et al. (1999) reported constantly of internal nitrogen requirement at about 16 g Nkg-1 of total dry matter (haulms plus tubers). Crop recovery of fertilizers is usually high at high nitrogen rates. This was observed by kitur et al. (1984) when they found that the recovery was 75% at high nitrogen rates versus 38% at low nitrogen rates for the harvested grains stover.

     The response of potato to time of nitrogen application was studied by Elkashif et al. (2000), conducted the application of half dose after emergence and other half three weeks later resulted in the lowest emergence, poorest vegetative growth and lowest tuber yield.

     Differently finding obtained by Abu Zeid et al. (1997) who found yield and yield components of potato were positively affected by splitting nitrogen fertilizer application, and result was show that low rate of 169 kg N/ha was gave higher yield than high rate of 226 kg N/ha. Jokela and Randel  (1984), and Mlyarek et al., (1984). They recorded significant increase in the grain yield of corn and nitrogen uptake in response to the added nitrogen and that the recovery of nitrogen fertilizer increased with the rate of the nitrogen added. Also they found that the varieties with maximum and minimum grain yields corresponded to the maximum and minimum value of nitrogen supply.

     Milthorpe and Moordy (1974) stated that tuber growth is associated with nitrogen partitioning from leaves into the tubers. Chevalier and Schrader (1977), remobilization of nitrogen from stalks and leaves may be an important source of nitrogen for deposition in the grains. Genotypes differ for nitrogen immobilized and partitioning of nitrogen in the plant. Many research workers explained that translocation of nitrogen from stalks took place soon after silking while remobilization from the leaves was greatest during the end of grain fill (Hanway, 1963). Similarly, Chandler (1960) reported relatively more translocation from both leaves and stalks later in the grain-filling period than in the first several weeks after silking. Although Anderson et al., (1980) found that maximum nitrogen accumulation occurred in the last half of grain fill. These reports indicate that nitrogen supply can affect prolific expression of some corn genotypes although reports conflict as to how prolificacy (kernels per ear or ears per plant) affects dry matter ( DM) accumulation during grain fill. Remobilization of nitrogen from leaves and stalks is important in the efficient utilization of plant nitrogen.

Effect of Nitrogen on crop growth:

The amount of nitrogen uptake by crop has a major impact on overall crop growth rate. The dependence of the crop growth on crop nitrogen relies on several processes examined by leaf photosynthesis-N relationship, the distribution of nitrogen between leaves, leaf expansion and positioning and subsequent impact on light interception (Novoa and Loomis, 1981; Sinclair and Shiraiwa, 1993). This consistent with the fact that the rate of crop growth is directly proportional to the amount of radiation intercepted which, in turn, is determined mainly by leaf production (Biscoe and Gallagher, 1978; Biscoe and Willington, 1983). The effect of nitrogen supply is to increase the crop surface area (Spiertz and Ellen, 1978; Spiertz and Van de Haar, 1978; Biscoe and Willington, 1983)

Haulm Growth and leaf area index (LAI):

     Hay and walker (1989), state that leaves begin to be produced as a regular series of primordia, localized out growths on the sides of the apical dome of vegetative shoot. However, Milthorpe and Moorby (1974) reported that a leaf arises as a lateral appendage of the stem. Moll (1983) found that higher yielding potato cultivars had high leaf area indices as well as high photosynthetic rates.

Coulson (1982), mentioned that the high yield of tuber was due to a larger leaf area developed quickly during the life cycle of the plant. Perumal (1981) reported that in early planted crops, the leaf area index was initially low, but it gradually increased to its maximum level with the onset of tuber bulking. In late planted crops, the leaf area index attained its maximum level earlier. Hruska (1975) found that the leaf surface area per plant increased with decreasing the plant density, but it was inadequate to compensate for the fall in number of plants per unit area. Gunasena (1968); Harris (1971); and Nahdi, (1977) suggested that the increase in leaf area would increase tuber yield. Leaf area index between 3 and 4 will be optimum for potatoes; this mean that there is 3 - 4 m2 of the leaf area per square meter of the soil. The assimilation per unit leaf area depends mainly on carbon dioxide and water supply in order to form 1 kg of dry matter. Khurana and Maclean (1982) reported that potato crop growth has been considered in terms of leaf area index, leaf area duration and assimilation rates.

Tuberization:

     Potato tubers are shortened and thickened modified stems that bear scale leaves (cataphylls) each with a bud in its axil (Cutter, 1978). The usual site of tuber formation is a stolon tip. Stolons (rhizomes) are diagravitropic stems with long internodes and scale leaves. They develop as branches from underground nodes and are terminated by a curved apical portion called a hook (Peterson et al., 1985). According to Plaisted (1957) stolon formation starts at the most basal nodes and progresses acropetally.

     The potato plant is remarkable for its plasticity in organ development (Steward et al., 1981; Clowes & MacDonald, 1987). Tuber formation can occur on almost every bud of the plant including axillary buds (Ewing 1985) and inflorescence (Marinus, 1993). The signal for induction to tuberization is omnipresent (can be transported to every plant part) and can express itself in all buds (Struik et al., 1999).

     Potato tuberization is a complex process involving anatomical, enzymatic, biochemical and hormonal changes leading to the differentiation of the stolon into a vegetative storage organ, the tuber (Xu et al., 1998, Jackson, 1999; Fernie and Willmitzer, 2001).

Anatomical changes:

     It has been reported that transformation of stolon into tuber involves cell division, change in the direction and orientation of the microtubule, and cell enlargement (Koda, 1997). During tuber initiation many changes have been documented to occur in stolon tips. Xu et al. (1998) observed cell division in the apical and subapical regions (up to approximately 5 mm from the apex) of non-swelling but elongating stolons. Upon tuber initiation, cessation of stolon growth concides with the cessation of mitotic activity in the apical meristems (Xu et al., 1998). Both cell division and cell enlargement contribute to the development of tubers (Xu et al., 1998).

Biochemical changes:

     Biochemical changes associated with tuberization have been investigated by several molecular biologists (Park 1990; Prat, et al., 1990; Sanchez-Serrano and Et, 1990). Before any sign of tuber initiation, stolon tips undergo a change that increases the accumulation of soluble carbon compounds and increase the conversion of these to insoluble compounds (Oparka and Davies, 1985).    

Efficient use of nitrogen fertilizer:

     Nitrogen have the transitory nature in the soil, its tendency for loss from the soil, and its potential for becoming a pollutant of air and water, fertilizer nitrogen should receive more care in its overall management than any other of the primary and secondary plant nutrients. Nitrogen can also have a more deleterious impact on the chemical properties of many soils than other major fertilizer nutrients due to its tendency to accelerate soil acidification processes.

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