Optimum Nitrogen and Phosphors Fertilizer Rates for Upland Rice Production in North Western Ethiopia

Tilahun Tadesse^1*, Zelalem Tadesse¹, Habtamu Asega¹, and Christian Tafere¹

¹Fogera National Rice Research and Training Center, Woreta, Ethiopia

^*Corresponding author: tilahuntadesse2000@gmail.com

Abstract: The national average yield of rice is about 2.8t ha^-1 which is lower compared to the world average productivity of 4.6 tones ha^-1 mainly constrained by soil nutrient deficiencies. An experiment on nitrogen and phosphorous fertilizer rates was conducted on upland rice on Nerica-4 variety in Fogera and Libokemkem districts in three consecutive main cropping seasons of the years 2015, 2016 and 2017 to determine the appropriate rates for production. The treatments were comprised of factorial combinations of four nitrogen rates (0, 46, 92,138 N kg ha^-1) and three phosphorous rates (0, 46, 92 P₂O₅ kg ha^-1), and laid out in randomized complete block design (RBD) with three replications. Data were collected on plant height, panicle length, and number of total tillersm-2, number of fertile panicles m-2, thousand seeds weight, grain yield, straw yield and harvest index. All collected data were subjected to analysis of variance. Economic analysis was also carried out by following CIMMYT (1988) procedures. The results of the experiment indicated that the main effect of nitrogen application significantly affected plant height, panicle length, total tillers, number of fertile panicles, grain yield, and straw yield, while that of phosphorous significantly affected total tillers, number of fertile panicles and grain yield. The interaction of nitrogen and phosphorous was significantly affecting total tillers, number of fertile panicles, grain yield and straw yield. The highest grain yield (5.5 t ha^-1) was obtained from the interaction of 138 kg ha^-1N with 46 kg ha^-1 P₂O₅. The economic analysis has further revealed that the combined application of 138 kg ha^-1N and 46 kg ha^-1 P₂O₅ which gave the highest net return of Birr 68,307.5 ha^-1 was the most profitable treatment to upland rice production. Thus it is concluded that application of nitrogen and phosphorous fertilizers at the rates of 138-46 N-P₂O₅ kg ha^-1 is the best to be recommended for rainfed upland rice production in the study area and other similar agro-ecologies.

Keywords: Nitrogen, Phosphorous, Productivity, Profitability, Upland rice.

1. Introduction

Rice (Oryza sativa L.) is an annual cereal crop and it is one of the most important food crops for the world’s population, especially in South Asia, Middle East, Latin America and West India (Zhao et al., 2011). It is the principal food for one third of the world’s population. More than 90% of rice is produced and consumed in Asia (Subedi et al., 2019). It provides some 700 calories per person, mostly residing in developing countries. In Ethiopia, rice production was started three decades ago in the early 1970's and the country has reasonable potential to grow various rice types mainly in rain fed lowland, upland and irrigated ecosystems (Mulugeta and Heluf, 2005). Although rice is a recent introduction to the country, its importance is well recognized as the production area coverage of about 10,000 ha in 2006 has increased to over 63,000 ha in 2018 (CSA 2019). The area coverage in domestic rice production has increased considerably linked with expansion of production in the wetland and upland areas with the introduction of suitable rice varieties for the agro-ecologies. In line with the area expansion, the production levels have been increasing consistently over years. CSA (Central Statistical Authority) data indicates that rice production has increased from 71,316.07 tons in 2008 to 171,854.09 tons in 2018 (CSA, 2019). The number of farmers engaged in rice production has also grown year after year. Rice production has brought a significant change in the livelihood of farmers and created job opportunities for a number of citizens in different areas of the country. Currently, Amhara, Southern Nations Nationalities and Peoples Region (SNNPR), Oromiya, Somali, Gambella, Benishangul-Gumuz, and Tigray regions are the rice producing areas in Ethiopia (MoARD, 2010). The Amhara region takes the lion’s share of producing the crop and accounted for 74-81% of the area coverage and 78-85% of the production in the years of 2016-2018 (CSA, 2016; CSA, 2017; CSA, 2018). According to the report of MoARD (2010), the potential rice production area in Ethiopia is estimated to be about 39,354,190 hectares, of which 5,590,895 ha is highly suitable, 24,910,629 ha are suitable and 8,852,666 are moderately suitable. Most of Ethiopia’s rice production potential area lies in the western part of the country.

Upland rice could suitably grow in many parts of Ethiopia. Predominant potential areas include west central highlands of Amhara Region (Fogera, Gonder Zuria, Dembia, Takusa and Achefer), North West lowland areas of Amhara and Benshangul Regions (Jawi, Pawi, Metema and Dangur), Gambella Regional State (Abobo and Etang Woredas), South and South West Low lands of Southern Nations, Nationalities and Peoples Region (SNNPR) (Beralle, Weyito, Omorate, Gura Ferda and Menit), Somali Region (Gode), Afar and South western highlands of Oromia Region (Illubabora, East and West Wellega and Jima Zones) (Dawit, 2015). The national average yield of rice is about 2.8t ha^-1 (CSA, 2018), which is lower compared to the world average productivity of 4.6 t ha^-1 (FAOSTAT, 2018). Weeds, pests, soil nutrient deficiencies and terminal moisture stress are the major causes of low rice productivity in Ethiopia (MoARD, 2010; Gebey et al., 2012). Poor soil fertility is among the major factors limiting rice production in Ethiopia. Nitrogen, phosphorus, and potassium are applied as fertilizers in large quantities to rice fields and a deficiency of either of the nutrient leads to yield losses (Aamer et al., 2000; Sharada et al., 2018; Masni and Wasli, 2019; Subedi et al., 2019). Nitrogen and phosphorus are often cited as the most limiting nutrients in agricultural soils of Ethiopia (Molla and Sofonyas, 2018). Appropriate fertilizer application is an important management practice to improve soil fertility and production of rice (Maneesh et al. 2018). Unlike the rain fed lowland ecosystem, fertilizer recommendations were not developed for the rain fed upland ecosystem of the study area. Therefore, a fertilizer experiment was conducted on the upland rice production of Fogera and Libokemkem Woredas in order to recommend appropriate levels of nitrogen and phosphorous rates.

2. Materials and Methods

An experiment on nitrogen and phosphorous plant nutrients was conducted on upland rice in Fogera and Libokemkem districts in three consecutive cropping seasons of the years of 2015, 2016 and 2017on a total of twelve on farm sites. The study at Fogera area is situated at 11 °54.4'46.3''N to 11 °57'03.0''N latitude and 37 °41'23.9''E to 37 °42'32.2'' E longitude at elevation range of 1787-1812 meter above sea level. The geographical location of the experimental area at Libokemkem is located at 12º 1′ 30″ N to 12º 12′ 00″ N latitude and 37º 31′ 30″ E to 37º 52′ 30″ E longitudes with the altitude range of 1804 to 1910 meter above sea level. The study site receives mean annual rainfall of1219 mm with annual average minimum and maximum temperature of 12.75°C and 27.37°C, respectively. The long-term rainfall data (1986-2017) indicated that much of the rainfall occurs in July and August (Figure 1).

Figure 1: Mean monthly total rainfall, and monthly average minimum and maximum temperatures of the study area for the period 1981-2017

Composite soil samples for each experimental site was collected before planting for major physical and chemical analyses using the standard procedures. The soil samples were collected, air-dried, ground, sieved to pass a 2-mm mesh and composited into one. Soil analysis was carried out from the composite sample in duplicates where soil samples were analyzed for soil texture using Bouyoucos hydrometer method (Bouyoucos, 1962). Total nitrogen following the Kjeldahl procedure method (Sahlemedhin and Taye, 2000) and Soil was also analyzed for pH (1:2.5 soil: water) by using pH meter (Sahlemedhin and Taye, 2000). While organic carbon was determined using wet digestion method (Walkely and Black, 1934) available phosphorus was using Bray II method (Bray, 1954).

The textural class of the experimental soil was found to be heavy clay with the pH of 5.87-6.08, which is slightly acidic and it is a preferred range for most crops (Table 1). Total nitrogen content was 0.09-0.11%, which is within the range of low levels (0.02-0.5%) for tropical soils. The organic matter content of the soil was 2.13-2.39%, which is within a range of medium (2-4%) for Ethiopian soils as per criteria developed by Murphy (1968). The available P content of the experimental soil was 11.4-25.13ppm that lies in a range of deficiency (< 20-40mg/kg) for most crops (Landon, 1991).

The treatments were comprised of factorial combinations of four nitrogen (0, 46, 92, 138 N kg ha^-1) and three phosphorous levels (0, 46, 92 P₂O₅ kg ha^-1) in Randomized Complete Block Design and replicated three times. The gross size of the experimental plots was 3m x 4m consisting of 15 rows planted at a spacing of 20 cm apart with the seeding rate of 100 kg ha^-1. The net plot area was made by excluding the left and right outer rows and a plot length of 0.5 m from the top and bottom sides of the plot. The final net plot size was thus 2.6m x 3m. Data on plant height, panicle length, number of total tillersm-1 row length, number of fertile panicles m-1 row length, thousand seeds weight, grain yield, straw yield and harvest index were collected timely from the net plot areas following their respective standard measuring methods and procedures. The rice grain yield and thousand seeds weight were adjusted at 14% standard moisture content. All collected data were subjected to analysis of variance (ANOVA) using SAS software version 9.0 (SAS-Institute, 2003). Since the test of homogeneity of variances for each parameter was non-significant, combined analysis of variance was done over the years to determine the effects of nitrogen and phosphorous fertilizers on rice production. Wherever the ANOVA results showed significant difference between treatments for a variable, mean separation between treatments was executed by using Least Significant Difference (LSD) method at probability levels of 0.01 or 0.05 depending on the ANOVA results. Moreover, agronomic efficiency (AE) was calculated to assess the use efficiencies of the applied N rates as follows:

Where:

AE = agronomic efficiency
Gf = grain yield of the fertilized plot (kg)
Gu = grain yield of the unfertilized plot (kg)
Na = rate of applied N fertilizer (kg)

Economic analysis was carried out by following CIMMYT (1988) procedures by taking all variable costs. The prevailing cost of inputs and out puts in year 2019 were considered for the analysis. The costs of Urea and NPS fertilizers for the stated period at the study area were Birr 13.1 and 14.3 per kg, respectively, while the prices of rice grain and straw were Birr 13.5 and 1.2 per kg, respectively.

3. Results and Discussion

The analysis of variance indicated that plant height and panicle length of upland rice were highly significantly (P<0.01) affected by the main effects of nitrogen rates, but not by phosphorous rates and their interaction (Table 2). The highest plant height was recorded at the highest nitrogen rate of 138 kg ha^-1, while the lowest plant height was recorded at the control without N application (Table 2). The highest panicle length of upland rice exhibited at the rate of 138kg ha^-1 N, which was statistically at par at the rate of 92 kg ha^-1 N (Table 2) whereas, the lowest panicle length was observed at the control without N fertilizer application. In line with the present results, Ghorbannia et al. (2012), Shiferaw et al. (2012), Riste et al. (2017) and Molla and Sofonyas (2018) reported significant effects of N application on plant height and panicle length. Shiferaw et al. (2012) observed higher plant height (113.9 cm) at 92 kg which was statistically at par (113.5 cm) with 138 kg N ha^-1.The increase in plant height of upland rice in response to the increase of N fertilizer rates was probably due to enhanced availability of N, which enhanced further cell division and more leaf area that in turn resulted in higher photo assimilates and thereby resulted in more dry matter accumulation (Shiferaw et al. 2012). Similarly, Ghorbannia et al. (2012) observed that shorter plant height (105.4 cm) was noted at the control without N fertilizer application. On the contrary, they observed also longer height of 109.3 and 111.3 cm at 50 and 100 kg N ha^-1, respectively. Riste et al. (2017) stated that highest and significant panicle length (27.06 cm) was recorded with application of fertilizer dose at 60 kg Nha^-1compared to the control without N fertilizer. On the other hand, Molla and Sofonyas (2018) reported longest panicles of 20.19 cm at the rate of 46 kg N ha^-1, while they noted shortest panicles in the control plots. Similar to the present results, Shiferaw et al. (2012) reported also the longest panicle length at the rate of 138 kg N ha^-1.

The analysis of variance for number of total tillers and number of fertile panicles showed that the main effects of nitrogen and phosphorous on both yield components were highly significantly (P<0.01) and significantly (P<0.05), respectively. The interaction of N and P significantly (P<0.05) affected the number of tillers, but not the number of fertile panicles (Table 2). The highest number of total tillers and fertile panicles was recorded at the highest rate of 138 kg ha^-1 N while their lowest number was observed at the control without N fertilizer application (Table 2). Similarly, the highest number of total tillers and fertile panicles were exhibited at the rate of 92 kg ha^-1 P₂O₅, which were statistically at par at the rate of 46 kg ha^-1 P₂O₅. Number of total tillers was significantly responding to the interaction of nitrogen and phosphorous fertilizer applications. The highest number of total tillers was observed at the interaction of 138 kg ha^-1 N and 92 kg ha^-1 P₂O₅, while the lowest number of total tillers was recorded at the interaction of the controls without application of both N and P fertilizers (Table 2).In conformity with the results of the present experiment, Kumar et al. (2017) had reported maximum number of total and effective tillers m-2 with application of 150 kg N and75 kg P₂O₅ kg ha^-1. On the other hand, Riste et al. (2017) reported maximum number of tillers and panicle m-2at the rate of 120 kg N and 90 kg P₂O₅ kg ha^-1. Ghorbannia et al. (2012) exhibited that the most fertile tiller number was obtained at the interaction of 50 kg N and 75 and 150 kg P₂O₅ ha^-1, while they were observed the least tiller number at the interaction of the controls with NP fertilizers. According to Molla and Sofonyas (2018), application of 69 kg N and 20 kg P₂O₅ ha^-1 resulted in highest number of seeds (126.9) per panicle of rice than other combination rates. Application of NP fertilizers at optimum rates might result in superior growth and development that eventually reflected with significantly superior yield attributes (Kumar et al., 2017; Riste et al., 2017). Inferior crop growth in the controls without NP applications might closely be associated with insufficient availability of NP below their optimal requirements (Riste et al., 2017).

Thousand seeds weight was not affected by the main and interaction of the nitrogen and phosphorous rates. In contrary, the grain yield was highly significantly (P<0.01) affected by the main and interaction effects of nitrogen and phosphorous (Table 2). Concerning the nitrogen rates, the highest grain yield was shown at 138 kg ha^-1 N while the lowest was noticed at 0 kg ha^-1 N. In the case of the phosphorous rates, the highest grain yield was exhibited at 92 kg ha^-1 P₂O₅ which are statistically at par with the vales of 46 kg ha^-1 P₂O₅ (Table 2). With regard to the interaction effect, the highest grain yield (5.5 t ha^-1) was obtained at 138-46 N-P₂O₅ kg ha^-1, which was statistically equivalent with the yield (5.2t ha^-1) of the 138-92 N-P₂O₅ kg ha^-1 application (Table 2).

The straw yield was highly significantly (P<0.001) affected by the main effect of nitrogen but not by phosphorous (Table 2). The interaction of nitrogen and phosphorous significantly (P<0.005) affected the straw yield (Table 4). Regarding the nitrogen rates, the highest straw yield was seen at 138 kg ha^-1 N while the lowest was noticed at 0 kg ha^-1 N. With respect to the interaction effect, the highest straw yield (6.6 t/ha) was obtained at 138-92 N-P₂O₅ kg ha^-1 which is statistically at par with some of the treatment combinations (Table 2). The rice harvest index was highly significantly (P<0.001) affected by the main effect of nitrogen but not by phosphorous and the interaction (Table 2). The highest harvest index, among the nitrogen rates was recorded for 138 kg ha^-1 N that was statistically equivalent with the value of 92 kg ha^-1 N while the lowest was noticed at 0 kg ha^-1 N (Table 2).In support of the present finding, Kumar et al. (2017) stated that the grain and straw yields of rice increased up to application of 150:75 N-P₂O₅ kg ha^-1. Masni and Wasli (2019) had also reported that the grain and straw yields of upland rice were significantly affected and best at 60N and 35 kg P kg ha^-1. Molla and Sofonyas (2018) reported significantly higher grain and straw yields of upland rice at Tselemti District, north Ethiopia and the highest values were obtained in plots receiving 69 kg N ha^-1 and 30 kg P fertilizer ha^-1.The reports of Riste et al. (2017) revealed that paddy and straw yields of rice were influenced significantly (p < 0.05) under various combinations of N and P levels. The authors further explained that the treatment where N and P were integrated at the rate of 120 and 90 kg ha^-1 exhibited the highest paddy yield (4.5 t ha^-1) which was 56% more over control. Riste et al. (2017) has further described that highest straw yield (9.7t ha^-1) was recorded at 150 kg N + 75 kg P₂O₅ ha^-1.

The better grain and straw yields at the higher rates of N and P nutrients may be attributed to the fact that application of fertilizer may have resulted in optimum levels of nutrients for crop uptake and translocation to sink thereby expressing superior crop growth and development (Riste et al., 2017). Similar with the observation of highest harvest index at the current experiment, Worou et al. (2017) had reported higher HI (0.31) of upland NERICA rice with fertilizer (N at 80 kg ha^-1 as urea combined with P at 80 kg P₂O₅ ha^-1) than without fertilizer (0.21). Higher grain yields in the fertilizer treatments were associated with higher harvest index.

The analysis of the Agronomic Efficiency (AE) for the nitrogen indicate that the maximum AE of 29.74 was exhibited at 46 kg ha^-1 N, then the AE reduce to 13.92 at 92 kg ha^-1 N, and become lowest (4.32) at 138 kg ha^-1 N (Table 3). AE N is usually higher at low N rate than at high N rate (Gewaily et al., 2018; Yasuhiro et al., 2019). In tropical Asia, with proper crop and water management, AEN should be typically in the range of 20–25 kg kg-1 (Yasuhiro et al., 2019). Yoshida (1981) estimated better agronomic N use efficiency to be 15–25 kg rough rice per kg applied N in the tropics. Peng et al. (2010) reported that agronomic N use efficiency was 15 to 18 kg kg-1 N in the dry season in the farmers’ fields in the Philippines. In China, agronomic N use efficiency was 15–20 kg kg-1 N from 1958 to 1963 and declined to only 9.1 kg kg-1 between 1981 and 1983 (Peng et al., 2010). Since then, agronomic N use efficiency has further decreased in China because of the increase in N rate (Peng et al., 2010). Generally, fertilizer N use efficiency of ice at the highest rate is relatively low due to loss of applied N through leaching, volatilization and denitrification, which necessitate the need for improved N fertilizer practices to reduce environmental impacts and increase economic benefits of N fertilization (Fageria and Baligar, 2001). The lower agronomic efficiency at the highest N rates in the current experiment indicate that emphasis should be given to efficient nitrogen application methods like the split applications, use of slow N releasing fertilizer sources and real time N management so as to reduce the wastage of N in the upland rice production system of the study area.

Following the CIMYYT (1988) partial budget analysis method, grain and straw yield adjustments, calculations of total variable costs (TVC), gross benefits (GB) and net benefits (NB) were performed (Table 4). Dominance analysis was carried after arranging the treatments in their order of TVC. A treatment will be considered as dominated if it has higher TVC but lower NB than a previous treatment with lower TVC and higher NB (Table 5). Non-dominated treatments were taken out and marginal rate of return (MRR) was computed (Table 8). According to the CIMYYT (1988) partial budget analysis methodology, treatments exhibiting the minimum or more MRR (>100%) will be considered for the comparison of their NB. Highest NB (Birr 68,307.5ha^-1) with acceptable level of MRR (668.5%) was observed at 138-46 N-P₂O₅ kg ha^-1 (Table 6). In agreement to the present finding Irfan et al. (2016) reported that rice genotypes performed efficiently at 120 kg N + 90 kg P₂O₅ ha^-1 where highest paddy yield, net production value and profit were obtained. The combined application of nitrogen and phosphorous at 138-46 N-P₂O₅ kg ha^-1 is the most profitable rate to be recommended for rice production in Fogera plain.

4. Conclusions and Recommendation

The national average yield of rice in Ethiopia is about 2.8 t ha^-1, which is lower compared to the world average productivity of 4.6 tones ha^-1. Soil nutrient deficiencies and terminal moisture stress are among the major causes of the low rice productivity. Based on the results of the present study the highest grain yield and economic profitability of rice was obtained by the application of 138-46 N-P₂O₅ kg ha^-1, which can be recommended for rain fed upland rice production in the study area and other similar agro-ecologies. Future research works towards the improvement of nitrogen use efficiency of rice are also recommended.

Conflict of Interest

The authors declare that there is no conflict of interest

References