Enhancement of Growth, Yield and Nitrogen Use Efficiency in Rice Under the Application of Coated Urea

Enhancement of Growth, Yield and Nitrogen Use Efficiency in Rice Under the Application of Coated Urea

Glory K.S* , S. Jothimani , P.T.Ramesh , J.Rajkumar

Department of Soil Science & Agricultural Chemistry, Agricultural College & Research Institute, Tamil

Nadu Agricultural University, Killikulam, Vallanadu – 628 252, Thoothukudi District, Tamil Nadu, India

Corresponding Author Email: glorysunny448@gmail.com

DOI : http://dx.doi.org/10.53709/ CHE.2021.v02i03.09


The nitrogen losses from applied Nitrogen fertilizers are around 50% and contribute significantly to low nitrogen use efficiency. The use of coated fertilizer decreases the ammonia volatilization loss and thus could be an easy tool to increase nitrogen use efficiency. A study was therefore conducted to assess the impact of four levels of nitrogen (0, 50, 75, and 100% STCR N) coated with six materials (potassium chloride, sulphur, iron pyrite, gypsum, and fly-ash along with uncoated urea) on growth, yield and nitrogen use efficiency of rice. The tiller density (524 no/m2), SPAD value (42.80), productive tillers (491 no/m2), number of grains per panicle (231), panicle length (23.75 cm), 1000 grain weight (15.67 g),  grain yield (6582 kg/ha) and straw yield (7590 kg/ha) were more under the application of  100% STCR recommended N. However, the coated N fertilizer, coated urea increases the foresaid growth and yield parameters than the uncoated urea.  Among the coated N fertilizers, fly-ash coated urea produced the maximum tiller density (441 no/m2), SPAD value (38.63), productive tillers (440 no/m2), number of grains per panicle (208), panicle length (22.78 cm), 1000 grain weight (14.56 g), grain yield (6102 kg/ha) and straw yield (7477 kg/ha). The 50% STCR recommended N as fly-ash coated urea enhanced nitrogen agronomic use efficiency by 43.45%, nitrogen recovery efficiency by 52.76%, and partial factor productivity by 18.30% compared to control. Therefore the application of 50% STCR recommended N as fly-ash coated urea is recommended to increase its use efficiency and decreasing ammonia volatilization losses besides in rice.


Coated Urea, Fly-ash, Nitrogen, Nitrogen Use Efficiency (NUE), Rice, Soil Test Crop Response (STCR)

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Rice is an important world food security crop that relies on chemical fertilizer to sustain high yields. The use of urea and urea-based fertilizers has increased considerably over the past 15 years. They currently account for approximately 50% of World agricultural Nitrogen consumption [1]. In the event of high input agriculture, more emphasis on fertilizer use efficiency, especially nitrogen use efficiency (NUE) has to be given to safeguard the economic and environmental resources under rice production. The nitrogen losses from applied N-fertilizers are around 50% and contribute significantly to low fertilizer use efficiency [2]. The low N-use efficiency is attributed to various N losses such as ammonia volatilization, denitrification, leaching, and runoff, etc. [3]. The proportion of N fertilizer lost is higher in rice fields than in other cereal crops due to rapid N losses through volatilization and denitrification in the submerged soil condition. A promising strategy to improving nitrogen use efficiency is the use of nitrification inhibitors and slow-release N fertilization. Controlled release of Nitrogen by coating can be used to increase urea fertilizer efficiency [4]. Due to the lesser-availability of nitrification inhibitors and slow release Nitrogen fertilizers, a custom made urea based coated fertilizer such as KCl coated urea, Sulphur coated urea, Iron pyrites coated urea, gypsum coated urea, and fly ash coated urea are used in this study to improve N use efficiency and yield of rice.

Coated nitrogen fertilizers are made to release nitrogen slowly into the soil solution thus maximizing its use efficiency by reducing nitrogen losses [5]. Potassium decreases volatilization loss by increasing calcium carbonate precipitation. Calcium is replaced by potassium which is precipitated as calcium carbonate and thus enhances the occupancy of ammonium in the exchangeable sites [6]. Sulphur coated urea reduced ammonia volatilization because of the low solubility of sulphur in water, thereby retaining ammonia for a greater period. Further, it prolongs the transformation of urea to ammonium and nitrate [7]. Gypsum can enhance the nitrogen use efficiency of urea and reduce the ammonia volatilization loss by 40% compared to prilled urea. Continuous usage of gypsum-coated urea also supplements the soil with Sulphur [8]. Around 54% reduction in ammonia loss was noticed with 1:5 (Urea: Pyrites) compared to urea alone. This is mainly due to the acidity produced by the adsorbed sulphates preventing the increase in pH around urea microsite [9]. Fly-ash retained higher ammonium nitrogen and nitrate nitrogen content compared to conventional compound fertilizers [10]. Fly ash is environmentally friendly and available at a low cost. Therefore the present study aimed to study the effects of nitrogen levels with various coating materials on rice’s growth, yield, and nitrogen use efficiencies.


A field experiment was conducted during the Pishanam season of 2020-2021 at the Farmer’s field in Murappanadu village, Srivaikundam taluk of Tuticorin district. Geographically the experimental site fell under the southern climatic zone and is located on the western bank of river Tamiraparani and lies at 8.712 N latitude and 77.830 E longitude. The field soil was clay loam in texture with a pH of 7.90 and Electrical Conductivity of 0.20 dS/m. The availability of N, P, and K was low, high, and high, respectively. The experiment was laid out in a split plot design with TKM 13 and replicated twice. Four levels of N as 0, 50, 75, and 100% STCR Recommended N under main plots and six coated fertilizers such as potassium chloride, sulphur, iron pyrite, gypsum, and fly ash along with uncoated urea under subplots were imposed.  Urea was coated with the respective materials in the ratio of 5:1 on weight basis. The prepared coated urea was applied as basal and top dressing at active tillering, panicle initiation, and heading stages of rice crop at the rate of 298 kg ha-1, 224 kg ha-1, and 149 kg ha1 to represent 100%, 75%, and 50% STCR recommended N respectively. Blanket recommendation of phosphorus as Single Super Phosphate at the rate of 312 kg ha-1 in single-doseas basal and potassium as Murate of Potash at the rate of 83 kg ha-1 in four equal splits were applied uniformly to all the treatments. The growth and yield parameters were recorded, and nitrogen use efficiency parameters such as Agronomic efficiency, Recovery efficiency, Partial factor productivity, and physiological efficiency were calculated according to the methods of [11].

All the data obtained were subjected to statistical analysis as suggested by [12]. The significant treatments were identified at 5% probability level, and non-significant treatments were denoted by NS. AGRES software for split-plot design was used to determine the significant difference between the treatments.


Growth and yield parameters

            The nitrogen levels and coated urea had a significant effect on the tiller density at different growth stages (Table 1). The nitrogen levels significantly enhanced the tiller density and enhanced as the N level increased from 0 to 100% STCR Recommended N application in all the physiological stages of rice.  The more tiller density of 458, 520, and 524 was recorded in 100% STCR N during tillering, panicle initiation, and heading stages of rice, respectively.

Table 1: Tiller density, SPAD Value and yield parameters as influenced by the main effect of coated urea and its level in rice

N1 – No  Nitrogen, N– 50 % STCR Recommended N, N3 – 75 % STCR Recommended N, N4 – 100 % STCR Recommended N, A– Uncoated Urea, A-KCl Coated Urea, A– Sulphur coated Urea , A– Iron pyrites coated Urea,A5 – Gypsum coated Urea,A6 – Fly-ash coated Urea

Table 2: Tiller density, SPAD Value and yield parameters as influenced by the interaction effect of coated urea and its level in rice

The increase in tiller density is due to the higher availability of nitrogen which plays a significant role in the cell division [13]. Similarly, coated urea always registered more tiller density compared to uncoated urea. Among the different coated urea, fly-ash coated urea recorded higher tiller density of 441, 460 and 464 no/m2 and was on par with sulphurcoated urea and iron coated urea during all the stages except where both fly-ash and sulphur coated urea were on par with each other during tillering, panicle initiation and heading stages of rice respectively. Inorganic sources such as fly-ash and sulphur offer more balanced nutrition, which positively resulted the number of tillers [14]. Tiller density is directly proportional to the amount of nitrogen absorbed by the crop [15].

            SPAD reading was also influenced by both nitrogen levels and coating urea. Application of coated urea makes the nitrogen available to the plant at all the stages, thus recorded more the SPAD value from tillering to heading stage, whereas it decreased in the control plot owing to its unavailability [16]. SPAD value was highest under the 100% STCR N and significantly differed from others (Table 1). SPAD measurement is an indirect measure of leaf nitrogen concentration and has a positive relationship with nitrogen levels [17]. All the coated urea showed higher SPAD values compared to uncoated urea, and highest (38.58, 38.28, and 37.27) under the fly-ash coated urea application during tillering, panicle initiation, and heading stage, respectively. Interaction between the nitrogen levels and coating urea significantly influenced the SPAD reading (Table 2). 100% STCR N as fly-ash coated urea had higher SPAD values of 43.37, 42.87, and 43.67 during tillering, panicle initiation and heading stage, respectively. Fly ash has high podzalonic properties, which act as a suitable adhesive for coating fertilizers and releasing nitrogen slowly without much loss [18]. Slow-release of urea and reduction in loss from the coated urea make the nitrogen more available to the plant than uncoated urea where losses would be more.  These results are in line with the findings of [19].

            Productive tillers is an important parameter for determining yield. Fertile tillers were significantly higher (491 no/m2) under the application of 100% STCR N and decreased with decreasing nitrogen levels (Table 1). All the coated urea produced higher productive tillers compared to uncoated urea. Among the coated urea, fly ash and sulphur coated urea had an equal impact on fertile tillers of 440 and 436 no/m2 respectively. A significant interaction was found between the nitrogen levels and coated urea (Table 2). 100% STCR N as fly-ash coated urea and sulphur coated urea were significantly on par with each other and produced higher fertile tillers of 521 and 513 no/m2,respectively.  Adequacy of nitrogen favored the proper cellular activities during panicle formation and development, which led to increased productive tillers. These findings are in close conformity with [20]. 

            The results revealed that nitrogen levels significantly influenced the panicle length. The length of the panicle raised from 19.48 to 2.74 cm by incremental application of nitrogen from 0 to 100% STCR recommended N (Table 1). The panicle length is enhanced with increase in nitrogen levels because of the fact that nitrogen takes part in panicle formation and panicle elongation. These findings agree with [21]. Among the coated urea, the longer   panicle length was recorded under fly-ash, KCl and sulfur coated urea followed by iron pyrites and gypsum coated urea. This was probably due to higher uptake of nitrogen and higher availability of soil nutrients [22].

            The number of grains per panicle had a positive response with nitrogen levels (Table 1). And recorded more under 100% STCR recommended N application (231 no/panicle). These results are in agreement with [23]. Uncoated urea significantly produced less grains/panicle of 163 no/panicle than fly-ash coated urea with 208 no/panicle. A significant increase in the number of grains per panicle was noticed under the coated urea over uncoated urea as reported by [24]. Application of 100% STCR N as fly-ash coated urea, sulphur coated urea, and KCl coated urea produced more grains per panicle of 259,256 and 246 respectively and were on par with each other (Table 2). The presence of potassium and sulphur in the coating have a positive interaction and are associated with the accumulation of metabolites that would increase carbohydrate or protein synthesis improving grain yield [25].

            The test weight  (Table 1) was also significantly influenced by both nitrogen levels and coated urea. Application of 100% STCR recommended N recorded higher test weight of 15.67 g. Similarly, fly-ash coated urea recorded a comparable higher test weight of 14.56 g. An increase in test weight at higher nitrogen levels might be due to the increase in leaves’ chlorophyll content, which led to higher photosynthetic rate and ultimately plenty of photosynthate available during grain development [26].

            Grain yield is a function of various yield parameters such as number of productive tillers, panicle length, number of grains per panicle, test weight etc., The Grain yield was increased with increase in nitrogen levels and maximum of 6582 kg/ha was registered by the 100% STCR recommended N application (Table 1) and observed that 36.81% increase was noticed in 100% STCR recommended N application compared to control. These findings are in agreement with the findings of [27] where the N fertilization showed a significant quadratic response to grain yield. Fly-ash coated urea registered a higher grain yield of 6102 kg/ha followed by sulphur coated urea with 5760 kg/ha, KCl coated urea (5622 kg/ha) , iron pyrites coated urea (5450 kg/ha) and gypsum coated urea (5265 kg/ha). Increase in grain yield of 17.06% was observed under the fly-ash coated urea compared to uncoated urea. Nitrogen from coated urea will be released at a slower rate all through the season. Thus, the carbohydrate contribution from the photosynthesis will be more efficiently translocated to the grain, leading to increased yield [28]. There was significant interaction among nitrogen levels and coating materials (Table 2). Application of 100% STCR N as fly-ash coated urea gave the highest yield of 7008 kg/ha (Figure 1) since the fly-ash contains several nutrients such as P, K, Ca, Mg, S, Zn, Cu, Mn which may have resulted better plant growth and yield [29].

Figure 1: Grain yield of Rice as influenced by the effect of nitrogen levels and coating materials.

As that of grain, the straw yield was also higher under the application of 100% STCR N   (7590 kg/ha) and 75 % STCR N (7319 kg/ha) which were statistically on par with each other. More straw yield could be explained as higher capability of rice to utilize more nitrogen through the expression of better growth by accumulating more dry matter. A similar observation was made by [30]. All the coated urea produced significantly higher straw yields compared to uncoated urea. Among the coated urea fly-ash coated urea significantly produced more straw yield of 7477 kg/ha which may be attributed to the sufficient supply of ammonium availability for a longer period of time [31].

The correlation relationship between grain yield and various yield parameters presented in Table 3 showed that the parameters such as productive tillers, grain yield, straw yield, no of grains per panicle, panicle length and test weight were highly significant and positively correlated with each other. The grain yield was highly correlated with productive tillers with the r2 value of 0.97, indicating the very strong positive relationship existed between them.

Table: 3 Correlation coefficients among yield parameters of rice

Nitrogen Use efficiency (NUE)

            The nitrogen use efficiencies such as AE, RE, and PFP were higher under the application of 50% STCR recommended N (Table 4) and decreased with increasing nitrogen levels. Coated urea had higher AE, RE, and PFP compared to uncoated urea. Fly-ash coated urea had higher AE, RE and PFP at all the nitrogen levels followed by sulphur, KCl, iron pyrites and gypsum coated urea. 50% STCR recommended N as fly-ash registered the maximum AE, RE, and PFP of 37.28, 72.81, and 88.51, respectively. Under the 50% STCR recommended N application, 43.45%, 52.76%, and 18.30% increase in AE, RE and PFP was observed in fly-ash coated urea compared to uncoated urea. All the coated materials enhanced plant nitrogen uptake and reduced N losses from urea, contributing to a significant increase in NUE [32]. Further, the coated urea application improved grain yield by increasing the photosynthetic potential of leaves and contributed to the enhanced NUE. PE being a varietal character, did not have a significant positive relation as that of other efficiencies. NPE reduced while AE, RE and PFP increased. These results are in accordance with [33].

Table 4: Nutrient Use efficiency as influenced by different levels and coating materials on Rice


            Application of 100 % STCR recommended N significantly registered more tiller density, SPAD value, productive tillers, number of grains per panicle, panicle length, and higher grain and straw yields of rice. However, the application of 100 % STCR recommended N as fly ash coated urea enhanced the above-mentioned growth and yield parameters of rice. The coated urea used in this study followed the trend of fly-ash > Sulphur > KCl > Iron pyrites > Gypsum. Even though, application of 100 % STCR recommended N registered more growth and yield, application of 50% STCR recommended N as fly-ash registered more agronomic efficiency, recovery efficiency and partial factor productivity besides the comparable grain yield. Therefore, application of 50% STCR recommended N as fly-ash is highly beneficial with higher nitrogen use efficiency and less ammonia volatilization.


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