Response of Improved and Local Potato (Solanum tuberosum L.) Cultivars to Nitrogen Fertilizer

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Published on International Journal of Food & Nutrition
Publication Date: May 15, 2019

Hailu Duguma Muleta, Nigussie Dechassa & Jemal Abdulahi
Arsi University, College of Agiculture & Environmental Sciences, Department of Plant Sciences
School of Plant Sciences, Haramaya University

Journal Full Text PDF: Response of Improved and Local Potato (Solanum tuberosum L.) Cultivars to Nitrogen Fertilizer (Study in Haramaya, Eastern Ethiopia).

A field experiment was conducted on a research field of Haramaya University during the 2012 main cropping season to determine the relative agronomic and tuber quality performances of potato varieties in response to nitrogen (N) application. The treatments consisted of four N rates (0, 55, 110 and 165 kg N ha-1), and two improved (Bubu and Zemen) and three local (Batte, Daddafa and Jarso) varieties. The experiment was laid out as RCBD with a factorial arrangement and replicated three times. Plot size was 4.5 m x 3.6 m (16.2 m2) accommodating six rows of plants at the spacing of 75 cm between ridges and 30 cm between plants. Net plot area was 3 m x 3 m (9 m2). The results revealed that increasing the rate of N from 0 to 55 kg N ha-1 significantly increased most of the measured parameters. However, increasing N beyond this level did not affect most of the parameters. Variety also significantly influenced many parameters. The interaction effects of N and variety were not significant on all parameters. Positively and highly significant associations were found for a number of the measured parameters. In conclusion, the results revealed that the optimum performances of all varieties occurred at the N rate of 55 kg N ha-1. In addition, improved variety Bubu, followed by Zemen, was superior to the other varieties in terms of tuber productivity.

Keywords: Varieties, Yield, Nitrogen Level & Growth.

Research findings have indicated that potato could be one of the most important crops to be introduced in the area where the population experiences recurrent malnutrition due to heavy dependence on cereal crops and poor crop productivity provided that appropriate agronomic practices are applied (Zelalem et al., 2009). Potato is regarded as a high-potential food-security crop because of its ability to provide a high yield of high-quality product per unit input with a shorter crop cycle (mostly < 120 days) than major cereal crops like maize (Hirpa et al., 2010). It has been stated by John J. Burke (2017) that at least six major potato roles can be assigned to the potato tuber. These include hunger-relieving crop, food (either fresh, processed), animal food, propagule (from which to produce the next crop), feed stock in industry for starch and alcohol, an item of commerce, and a resource of biodiversity. He also detailed that potatoes are grown and eaten in more countries than any other crop; they are grown in all the continents except Antarctica. In the global economy they are the fourth most important crop in total production and the fourth largest contributor to human caloric consumption, after the three cereals, rice, wheat and maize.
About more than 1.13 million farmers are potato growers in Ethiopia; and this crop added 29.84% of the area to the total root crop, and contributed 21.24% to the total root crop production (CSA, 2017/2018). Hirpa et al. (2010) indicated that potato is grown in four major areas in Ethiopia. These areas include the central, the eastern, the north-western and the southern regions (mainly located in the Southern Nations’, Nationalities’ and Peoples’ Regional State and partly in the Oromiya region). In this study they also stated that these areas together cover approximately 83% of the potato farmers.
Mulatu et al. (2008) pointed out that potato is the second most advantageous crop next to khat (Chata edulis) in supporting farmers’ welfare with 759% increase in income over sorghum (Sorghum bicolor (L.) Moench) which is the main staple cereal crop grown in Hararghe. Compared to the other areas of potato production, this area is characterized by export market oriented production particularly to Djibouti and Somalia (Hirpa et al., 2010). Similarly, Mulatu et al. (2005) stated that the development of potato culture in Hararghe, like other vegetables, is due to the presence of an export and cross-border market outlet to Djibouti and Somalia; it is also due to the presence of a domestic market in the major urban settlements of Hararghe, including Dire Dawa, Harar, Jigjiga, Asebe Teferi and several other towns. Most farmers grow local potato varieties namely, Batte, Jarso, Samune, Daddafa, Mashena dima, etc. throughout the year using irrigation and rainfalls (Anonymous, 2011). However, Mulatu et al. (2005) reported that some farmers targeted by research and extension as well as those involved in nongovernmental organization (NGO) seed programmes have access to improved varieties released by Haramaya University. Despite the use of local varieties, the productivity of potato in this area is equivalent to the productivity in the central area; this might be due to good farm management practices triggered by farmers’ market orientation.
The optimal response to N fertilizer application differs by cultivar (Kleinkopf et al., 1981; Johnson et al., 1995) and soil type. Similarly, the other finding indicated that nutrient elements efficiency is the relative yield of one genotype in a poor soil as compared to its yield in a favourite nutritional condition. Maximum efficiency of nutrient element use is obtained while its concentration is near to critical level, because without excessive amounts of element in plant tissues, the highest yield is gained. In view of that, the release of new potato cultivars requires additional revision to develop best management recommendations for N fertilization of potato and for optimization of tuber yield and quality (Saeidi et al., 2009).
Nitrogen is the mineral nutrient most commonly deficient in agricultural soils. As a result, in developed countries, farmers apply relatively high rates of N fertilizers. Soil-plant system inefficiencies prevent complete utilization of the N, leaving residual N in the soil, which is a waste of natural resources and cause for environmental concern (Hopkins et al., 2008). Worldwide, crops do not directly utilize about half of the applied N and the overall N use efficiency has declined with increasing N fertilizer use (Dobermann, 2005). On the other hand, as compared to the developed countries, in developing countries such as Ethiopia, Kenya and Uganda, the amounts of fertilizers applied to the potato crop are very low. For example, in a study conducted by Gildemacher et al. (2009), the amounts of FYM, N, and phosphorus applied to potato crop were estimated to be only 4 t ha-1, 43 kg N ha-1, and 101 kg P ha-1 in Kenya, 3 t ha-1, 30.6 kg N ha-1, and 33.4 kg P ha-1 in Ethiopia, and 2.2 t ha-1, 37.6 kg N ha-1, and 46.9 kg P ha-1 in Uganda, respectively.

A blanket recommendation of 110 kg N ha-1 (165 kg urea ha-1) and 90 kg P2O5 ha-1 (195 kg DAP ha-1), has been promoted in Ethiopia for a long time, without any formulation of the amount of farmyard manure to be used for production of the crop (Institute of Agricultural Research, 2000). An experiment conducted at Haramaya on clay soil indicated that application of 87 kg N ha-1 and 46 kg P2O5 ha-1 is needed for optimum potato production (Getu, 1998). Hence, fertilizer requirement varies across locations due to reasons such as difference in soil types, nutrient availability of the soil, economic factors of the area, moisture supply and variety (Zelalem et al., 2009). Although many potato varieties have been released in the country, there is lack of clear information regarding N fertilizer requirement, management of the individual cultivar for optimum tuber yield. This necessitates a continuous research towards the establishment of appropriate fertilizer rates for the newly released varieties for specific location. According to Atkinson et al. (2003), newer potato cultivars are becoming more widely grown because of improved characteristics such as earliness, yield, quality, and storability, and increased resistance to insects, pathogens, and other environmental stresses. Therefore, this experiment was carried out with the objective of evaluating the response of improved and local potato varieties to different rates of N fertilizer at Haramaya area.

2.1 Description of the study site
The experiment was conducted during the 2012 main growing season under rain-fed condition at research field on the main campus of Haramaya University. Haramaya is located at 9°26’N latitude, 42°30’E longitude and at an altitude of 1980 meters above sea level. The site received mean annual rainfall of 780 mm, with the mean minimum and maximum temperatures of 8.25°C and 24.4°C, respectively (Mohammed et al. 2013). The soil of the experimental site is a well drained deep alluvial with a sub-soil stratified with loam and sandy loam (Tamire, 1973). Analysis of the chemical and physical properties of the soil indicated that it has organic carbon content of 1.15%, total N content of 0.11%, available phosphorus content of 18.2 mg kg-1 soil, potassium content of 0.65 cmol kg-1 soil (255 mg K kg-1 soil), pH of 8.0, and percent sand, silt, and clay contents of 63, 20, and 17, respectively (Simrat, 2010). These results indicate that the soil is low in organic carbon and total N, high in exchangeable potassium, and medium in available phosphate (Landon, 1991; Ryan et al, 2001).

2.2 Description of experimental material
Two improved potato varieties (Zemen and Bubu) that were released by Haramaya University and three local varieties (Daddafa, Jarso and Batte) were used. Bubu was released in 2010 (Tekalign, 2011). It is recommended for the highlands of eastern and western Hararghe zones with an altitude ranging from 1650-2330 meter above sea level. Zemen was released in 2001 (Ethiopian Agricultural Research Organization, 2004). It is adapted to east and west Hararghe with an altitude of 1700-2000 meter above sea level that receives an annual rainfall of 700-800 mm.

2.3 Field experiment set up
The experiment was laid out in randomized complete block design (RCBD) in a factorial arrangement with four treatments and three replications. Treatments were 0, 55, 110 and 165 kg N ha-1, assigned to each plot randomly. The land was cultivated by a tractor and pulverized by human labour. The number of plots was 60, and the size of each plot was 4.5 x 3.6 m wide.

2.4 Soil sampling and analysis
Soil samples were taken randomly in a W-shaped pattern of the entire experimental field before planting. Five samples were taken using an augur from each arm of the W-shaped lines to the depth of about 0-30 cm from the top soil layer, and combined to a composite sample. This composite was air-dried, pounded and sieved through a 2 mm sieve. From this mixture, a sample weighing 1 kg was prepared, and finally analyzed. Soil pH was determined from the filtered suspension of 1:2.5 soils to water ratio using a glass electrode attached to a digital pH meter (Page, 1982). Soil texture was determined by modified Bouyoucos hydrometer method as described by Singh (1980).The sample was analyzed for total N, available phosphorus, potassium, and organic carbon contents. Organic carbon content of the soil was determined based on oxidation of organic carbon with acid dichromate medium following the Walkley and Black method as described by Dewis and Freitas (1970). Total N was determined using Kjeldhal method (Jackson, 1975). Available phosphorus was determined by extraction with 0.5 M NaHCO3 according to the methods of Olsen et al. (1954), and potassium was determined with a flame photometer after extracting exchangeable K from the soil with 0.5 N Ammonium-acetate at pH 7 (Hesse, 1971).

2.5 Planting and fertilizer application
Medium-sized and well sprouted potato tubers were planted on the ridges at a spacing of 30 cm between plants and 75 cm between rows. The tubers were planted at a depth of 10 cm and covered with soil (Ngungi, 1982). One row consisted of 12 plants, and one plot consisted of 6 rows. The spacing between plots and blocks were 1 m and 1.5 m, respectively. Net plot area was 3 m x 3 m (9 m2). The plants were fertilized equally with Urea (46% N) as source of Nitrogen and triple superphosphate (46% P2O5) as source of phosphorus for all the plots. Nitrogen (110 kg N ha-1) in the form urea, was applied at the specified rates in three splits (one fourth at plant emergence; half of it two weeks after emergence; and one fourth at the initiation of tubers/start of flowering) as topdressing. However, triple superphospate (46% P2O5) was applied as basal fertilizer at the rate of 90 kg P2O5 ha-1 at planting.
Other cultural activities such as weed control, earthing-up and fungicide application were equally applied for the whole experimental area. Controlling of weeds was performed by hoeing and by hand pulling/uprooting. Earthing-up was done to prevent exposure of tubers to direct sunlight, for promoting tuber bulking and for easily harvesting. Fungicide, Ridomil MZ 65% WP at a rate of 1.5 kg/ha which is diluted at a rate of 40 g per 20 litre water, was sprayed once a week for the control of potato late blight (Phytophthora infestans). It was sprayed two times during wet season when the plants were at vegetative growing stage. Fungicide, Ridomil MZ 65% WP (1.5 kg ha-1 which is diluted at a rate of 40 g per 20 litre water) was sprayed two times once a week to control potato late blight (Phytophthora infestans).

2.6 Data collection
All data for growth parameters were taken up on randomly selecting 5 plants from central rows in each plot. Days to flowering was recorded at about 50 percent flowering of plant population in each plot. Days to maturity was recorded when 50 percent of the plants of different treatments were ready for harvest as indicated by senescence of the haulms. Plant height was determined by measuring the height from the base to the apex of plants. To determine leaf area, plants were selected at 50 percent flowering; then leaf area index was estimated from individual leaf length via the formula developed by Firman and Allen (1989).
Log 10 (leaf area in cm2) = 2.06 x log10 (leaf length in cm) – 0.458. Leaf area index was obtained by dividing the value of leaf area by the area of land occupied by the plant using the formula: Leaf area index (LAI) = LAm x N /A. Where: LAm = mean leaf area; A = area (cm2) occupied by one plant in the cropping area; N = number of leaves on the plant