INTRODUCTIONCrpos which are cultivated for their roots are known as root crops. Root crops contain mainly starch. Their water content is very high. These crops grow generally as annual crops and yield roots, tubers, rhizomes, corms and stems which are used largely for human food, either as such or in processed form, but also for animal feed. In certain countries, they are used to manufacture starch and alcohol. Beets, carrots, parsnips, radishes, turnips and rutabagas are all commonly known as root crops. These crops offer a prolonged harvest season and, for the most part, a long storage life. They also produce a large amount of food in a small amount of space.In root crops requirements of plant nutrients are different from others. Too much nitrogen fertilizer on carrots and potatoes in spring promotes foliage growth but not good tuber and root formation. Instead, root crops enjoy phosphorous, which promotes root growth, so a soil test should be performed and based on the results, bone meal or rock phosphate fertilizer can be added before planting to ensure quality yield. Onions in particular like lots of fertilizer, and they can stand some extra nitrogen, which promotes leaf growth.

SOIL MANAGEMENTLime and FertilizingRoot crops require a soil pH between 6.0 and 6.5. Strongly acid soils should be limed according to test results. Lime (if needed) is most effective when mixed thoroughly into the soil in the fall. It is also a good idea to side dress the plants with the same amount of fertilizer when the plants have reached about one-third their growth. To prevent burning the roots, however, fertilizer should be applied three to four inches away from plants. Soil PreparationRoot Crops grow best in well-drained, loose soil. Drainage is important because these crops are among the earliest planted and the latest harvested. Raised beds will help to reduce soil compaction, permit easier digging and will allow carrots and parsnips to attain greater length and be smoother in shape. Sand and organic matter can be added, as manure, to heavy soils to improve drainage. Using organic matter or manure that is not well-composed as a fertilizer for carrots can cause the roots to become rough and branched. The following steps may be used to prepare soil prior to planting in the spring: To apply two to three bushels of well-rotted manure or compost per 100 square feet. (If carrots are to be grown, it is wise to apply the organic matter in the fall prior for planting in the spring.) To apply recommended amounts of lime. To broadcast recommended amounts of fertilizer just prior to planting seeds and work into the soil.NUTRIENT MANAGEMENTPlants take up nitrogen as nitrate or ammonium, phosphorus as phosphate and potassium as potash. These chemicals, as fertilizers, can come from organic or inorganic sources. With adequate environmental conditions, soil microbes break down organic matter and supply the chemicals that plants need to their roots. Organic fertilizers can also improve soil tilth and health. Inorganic fertilizers can be used to supply a more readily available form of primary nutrients to plants.Organic fertilizers can come from a variety of sources such as manures, compost, fish meal and bone meal. Each material contains varying amounts of specific nutrients. Table 1 lists guidelines for nutrient management.Table 1: Annual nitrogen, phosphate and potash recommendations for root crops. Source:Delahaut and Newenhouse (1998)Fertilizer should be applied in a band 2 inches to the side of the row and 2 inches below the seed depth. On sandy soils nitrogen should be splited two to three applications over the course of the growing season. Too much nitrogen on carrots, radishes or parsnipes will cause excessive top growth. Carrots also need moderate amounts of manganese, borons and copper. Carrots grown in copper deficient muck soils have poor colour.Beets grown in soils deficient in boron will develop black spots in the phloem tissue and dry rot on the root surface. Boron deficiency is most common on calcarious soils and under drought conditions. Some plants such as muskmelon and sweet clover accumulate boron and their composted leaves may be added to soil to raise soil boron levels. Excessive boron in soils may cause poor beet seed germination. Rubatages are also susceptible to boron deficiencies and develop brown, water-soaked spots in the core of the root.Radishes need moderate amounts of boron, copper, manganese, molybdenum and zinc. Soil tests result will show recommendations to add zinc or to alter soil pH to make more molybdenum available.One of the goals of nutrient management is to supply nutrients in a timely manner to maximize crop yield and quality. Crop nutrient uptake is calculated from measurements of crop biomass (dry matter) multiplied by crop nutrient concentration.In onion, during early leaf growth phase nutrient needs are very low. Onions have a shallow, sparsely branched root system with most roots in the top foot soil. Rooting density increases with soil depth. The sparse, shallow rooting of onions has important implications for management of relatively immobile nutrients (P,K and some micronutrients such as Zn). The unbranched root system of onions is less effective than most crop plants in extracting immobile nutrients. Therefore onions are more susceptible than most crops to deficiencies of these nutrients.The shallow root system of onions also is an important consideration for efficient management of mobile nutrients such as nitrate-N and sulfate-S. With furrow irrigation mobile nutrients move to bed centers, where they typically become available later in the season when onion roots proliferate across the beds. Cumulative nutrient uptake by an onion crop follows a sigmoid or s-shaped curve during the growing season.

Fig. 1:Cumulative nutrient ( N,P,K,Ca,Mg,S) uptake by onion (bulb+leaf)

Fig.2: Cumulative nutrient (Mn,Cu,B,Zn) uptake by onion (bulb+leaf)Source: Horneck and Pelter (1998)The period of rapid nutrient uptake starts during bulbing. Onions take up more than 100lb per acre of nitrogen, potassium and calcium with substantially lower amounts of sulfur, phosphorus and magnesium (Fig. 1 and 2). About 80 percent of the nutrients present in the plant at harvest are present in the bulb; the remainder is present in tops.Potato growth can be divided into four distinct stages. Coordination of nutrient availability with the nutrient requirement of each growth stage has a profound influence on yield, specific gravity, and other quality characteristics.

Plant growth stages of potatoStage IPlant development after planting and until tuber initiation.

Stage IIBegins with initiation of tubers at the tips of stolons (tuberization) approximately 10 to 14 days prior to flowering. Tuberization is defined as an enlargement which is double the normal stolon diameter. Little or no enlargement of initiated tubers (bulking) occurs during this stage.

Stage IIIEnlargement of initiated tubers (bulking); tuber growth is linear if all growth conditions are optimum; tuber dry weight increases due to translocation of plant nutrients and food reserves from the shoots and roots into the tubers.

Stage IVTuber maturation occurs as vines start to yellow, leaf loss is evident.

Adapted from Kleinkopf and Westermann, 1981

Promoting rapid root development under the furrow improves water and nutrient efficiency during subsequent fertigation (applying liquid fertilizers through the irrigation system). Root elongation is most rapid during stage I, reaching 2 feet below the hill and into the furrow zone as early as 3040 DAP under optimum soil physical conditions (Pan et al., 1994). Although stolons can be initiated throughout most of the growing season, during early growth (stage I) the majority of stolonsare produced for tuber set. During emergence and initial growth, plant nutrients are supplied primarily from reserves in the seed piece until the plant establishes a leaf area of approximately 3162 inch2 or when plants have covered approximately 50% of the ground surface (using a 34-inch by 9-inch plant spacing) (Dean, 1994). Optimizing earliest tuber set should be a goal of the management system.

Early season nutrient management is critical for development of a healthy root system and preventing excessive vine growth during stages I and II. For short season (determinate) cultivars, tuber initiation begins when plants reach a genetically regulated shoot to root ratio. In the subsequent developmental stage (stage III), maximum tuber bulking occurs until plant senescence or environmental conditions end the growing season (Kleinkopf and Dwelle, 1978). High nutrient availability early in the growing season does not influence tuber initiation in shortseason (determinate) cultivars as strongly as in long season (indeterminate) cultivars. Short season cultivars generally have a greater early-season bulking rate which must be supported by greater early season nutrient availability than for indeterminate cultivars (Ojala et al., 1989). However, excess fertilizer application should be avoided at all growth stages for both short and long season cultivars toincrease fertilizer efficiency and minimize potential leaching or erosion losses of nutrients.An effective nitrogen fertilization program coordinates amount and timing of fertilizer application with plant demand and soil nitrogen supply. Poor nitrogen fertility management can lead to inefficient nitrogen utilization, which can reducecrop yield, tuber quality. Nitrogen is required in large amounts to maintain optimum shoot and tuber growth. The amount of nitrogen available to meet a crops requirement depends upon the efficiency of the management system. The potato plants nitrogen uptake efficiency under current best management practices is approximately 65% (Roberts et al., 1991), an efficiency which is comparable to that of corn and wheat.

For maximum tuber yields, phosphorus should be mixed into the seed bed prior to planting to support: early shoot and root growth (stage I), tuber initiation (stageII), and tuber bulking (stage III). Plant phosphorus levels in mid and late season (stages III and IV) may be raised by applications of phosphorus using foliar sprays, application through irrigation water, or soil applied phosphorus followed by irrigation. However, due to the small distances phosphorus moves in the soil, feeder roots must be near the soil surface to make in-season application effective.

At recommended potassium soil levels, yield does not appear to be directly related to increased application rates or source of potassium (KCl, K2SO4, or thiosulfate). In fact, applications in excess of recommended rates may be detrimental to potato quality (Tindall and Westermann, 1994; Westermann et al., 1994). High rates of potassium fertilizers may cause slight decreases in tuber specific gravity, which is especially important to potato used in processed products. However, there are reports of increased disease resistance with the use of potassium chloride. Crop consultants have not consistently seen significant differences in disease incidencerelated to potassium source. However, high rates of potassium chloride have been related to significant reductions in potato tuber quality (Lang and Stevens, 1997).

CONCLUSIONRoot crops are very important for us. Imbalanced nutrient management negatively affects the quality of root crops. So, proper nutrient management should be ensured to get high quality yield.

REFERENCES1. Dean, B.B. 1994. Cultivation, fertilization, and irrigation. In: Managing the potato production system. Haworth Press, Inc. New York. pages 69 83.2. Delahaut, K.A. and A. C. Newenhouse. 1998.Growing carrots, beets, radishes and other root crops in Wisconsin: A guide for fresh market growers, University of Wisconsin-Extension, Cooperative Extension, In Cooperation with the U.S. Department of Agriculture.3. Horneck, D. and G. Pelter. 1998. Nutrient Management for Onions in the Pacific Northwest. Oregan State University Extension Service.4. Kleinkopf, G.E. and D.T. Westermann. 1981. Predicting nitrogen requirements for optimum potato growth. Proc. Univ. Idaho Winter Commodity School. pages 8184.5. Kleinkopf, G.E. and R.B. Dwelle. 1978. Effect of nitrogen fertilization on tuber set and tuber size. Proc. Idaho Potato School. pages 2628.6. Lang, N.S. and R.G. Stevens. 1997. Survey of central Washington fertilizer recommendations. Proc. Wash. State Potato Conf. (In press)7. Ojala, J.C., J.C. Stark, and G.E. Kleinkopf. 1989. Influence of irrigation and N management on potato yield and quality. Amer. Potato J. 67:2942.8. Pan, W.L., L.K. Hiller, E. Lundquist, and R. Bolton. 1994. Potato root development. Proc. Farrow. 1991. Potato uptake and recovery of N-15 enriched NH4/NO3 from periodic applications. Agro. J. 83:378381.9. Roberts, S., H.H. Cheng, and F.O. Farrow. 1991. Potato uptake and recovery of N-15 enriched NH4/NO3 from periodic applications. Agro J. 83:378381.10. Tindall, T.A. and D.T. Westermann. 1994. Potassium fertility management of potatoes. Proc. Univ. Idaho Winter Commodity Schools 26:239 242.11. Westermann, D.T. and G.E. Kleinkopf. 1984. Phosphorus nutrition of potatoes. Proc. Univ. Idaho Winter Commodity Schools 16:215219.12. www.dummies.com/how-to/content/how-to-grow-root-crops.html13. www.uri.edu/ce/factsheets/sheets/rootcrops.html

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