Nitrogen Fertilization Practices of Farmers in Central Myanmar: Effect on Yield and Profitability in Monsoon Rice Cultivation

Nitrogen Fertilization Practices of Farmers in Central Myanmar: Effect on Yield and Profitability in Monsoon Rice Cultivation

Published: 2022.07.22
Accepted: 2022.07.22
5
Master’s Student
Department of Participatory Knowledge Management, Advanced Center for Agricultural Research and Education (ACARE), Yezin Agricultural University, Myanmar
Deputy Director
Advance Centre of Agriculture and Rural Education, Yezin Agricultural University
Associate Professor
School of Agriculture and Food, University of Melbourne, Parkville Campus, Australia

ABSTRACT

Chemical fertilizers play an important role in increasing agricultural production. Applying the right source of nutrients at the right time can minimize cost, increase yield and optimize profits. This study was carried out to identify nitrogen fertilizer application practices in monsoon rice production in central Myanmar and compare the costs and benefits of proper and improper practices of N-fertilizer application. A survey was conducted during February to March 2020. Four village tracts out of 49 village tracts in Tatkon Township were selected and personal interviews were conducted with 157 respondents by using a structured interview schedule. Various types of fertilizer application practices were found among the farmers and only 18% of farmers followed the fertilizer recommendation suggested by the Department of Agriculture. Common N supplements for monsoon rice cultivation were urea, ammonium sulphate, and compound fertilizers. The study revealed that per unit production cost of rice for proper nitrogen fertilization (PNF) group (US$124/MT {Metric ton}) was lower than that of improper nitrogen fertilization (INF) group (US$141/MT) which was significant at 10% level. Total variable cost was statistically significant at 1% level between two farmer groups, being higher in INF group (US$479/ha) than in the PNF group (US$426/ha). Benefit cost ratio (BCR) was also higher in PNF group with 2.12 than that of in INF group with 1.96, and gross margin of PNF group (US$500/ha) was also higher than that of in INF group (US$481/ha) although this difference was not statistically significant. Rice farmers in Myanmar may be able to reduce fertilizer and labor costs by practicing proper nitrogen fertilization techniques to increase both rice yield and profits.

Keywords: Proper nitrogen fertilization; monsoon rice production; cost of production; gross margin, BCR

INTRODUCTION

Rice accounts for the largest sown area of crops grown in Myanmar with 7.22 million hectares with the production of 28.01 million tons and the average yield of 3.92 metric ton per hectare in fiscal year 2018-19. It comprises 6.10 million hectares under monsoon paddy and 1.12 million hectares under summer paddy (MOALI, 2019).

Nitrogen is an essential nutrient for rice production. Nitrogen plays an important role in vegetative growth of rice plants that will lead to improved production. Proper fertilizer application can enhance proper conservation and secure more profits. Technology and investment in agriculture are generally recommended. Among agricultural technologies, fertilizer technology is highly recommended to obtain potential yield for crops. Fertilizer is the most expensive input for crop production. Therefore, farmers need to know about the importance of the proper application of Nitrogen nutrient in monsoon rice cultivation. The crucial goal for farmers is to obtain maximum profit with minimum cost. Therefore, the costly inputs must be efficiently and optimally allocated.

Excessive fertilizer use is harmful to the environment, but the level of fertilizer use in the crop production sector of Myanmar is far below the dangerous level (S.M. Than, H.L. Lynn and A. Phyo, 2018). According to the World Bank (2018), the rate of fertilizer consumption for Myanmar was 49.3 Kg/ha of arable land, compared to 148.9 Kg/ha in Thailand, 169.0 Kg/ha in the Philippines, 236.4 Kg/ha in Indonesia, 393.2 Kg/ha in China, 415.2 Kg/ha in Vietnam and 2,106.4 Kg/ha in Malaysia.

According to report of Flanders Investment and Trade Market Survey (2020), a total of 3.5 million tons of fertilizers is used in Myanmar’s agricultural sector consisting of: 44% Urea, 40% Compound, 7.8% T-Super, 4.5% Potash, and 3.7% of other fertilizers and overall application of chemical nutrients in Myanmar represents only 10% of the Southeast Asian regional average.

N-fertilizer, the most utilized and expensive input, is vulnerable to loss in many ways if not utilized properly and systematically. If applied incorrectly, up to 40% of the nitrogen applied as the form of Urea can be volatilized (vaporized) and lost as a gas (Funderburg, 2009). If applied it correctly, little, if any, nitrogen would be lost. The key is to apply the urea correctly. It must be used in a timely manner with right management. In reality, most farmers do not notice that the way they spend their investment on N fertilizer is not the most effective way of utilization. Different sources of N are Urea, Diammonium phosphate (DAP), Ammonium Sulphate, and Compound Fertilizers. Urea and Compound are mostly used fertilizers among Myanmar farmers. Most farmers used high rates of fertilizer, but with improper practices like using only one time of urea as basal application instead of split application and using compound fertilizer more than one time during one season of crop.

Farmers use fertilizers based on their availablity in the market regardless of the nutrient contents, effectiveness, brand and reliability of fertilizers. They do not have much concern about cost effectiveness or low-cost production or profit maximization perspectives. It is believed by farmers that the more they apply the fertilizer, the better will be the yield. Farmers will be able to obtain an optimum yield only when they can apply fertilizers in recommended rate and timely management.

Therefore, the research was conducted with the objectives of: (1) to identify nitrogen fertilizer application practices in monsoon rice production by farmers, and (2) to compare costs and benefits of proper and improper practices of N-fertilizer application in the study area.

RESEARCH METHOD

Description of the study area

This study was carried out in Tatkon Township which is located in northernmost part of Ottra District, Nay Pyi Taw Council Area. Tatkon Township is situated between Latitude 20° 20′ North and Longitudes 96° 30′ East. It is situated among the Shan State in the East, Mandalay Region in the North, Magway Region in the West and other townships of Ottra District in the South (Figure 1). The average annual temperature of Tatkon is 31 degrees celcius and the average annual rainfall is about 864 mm. Therefore, Tatkon has a fair weather where a wide range of cereals, vegetables, spices and cut flowers can be grown well. The various kinds of crops grown by most of the farmers in Tatkon Township are rice, maize, cotton, sugarcane, sunflower, groundnut, sesame, greengram, blackgram, lablab bean, chickpeas, chilli, watermelon and vegetables such as tomatoes, cabbage, cauliflowers, spinach etc. Therefore, the demand for fertilizer is ever increasing. There are about 40 agrochemical and fertilizer shops in Tatkon Township. The area of Tatkon Township is 180,237 hectares and cultivated area is 43,780 hectares, 24.3% of total area. The area of paddy land is about 21,145 hectares (48.3%) and dry land is about 22,627 hectares (51.7%) (DoA, 2014).

Sampling procedure

There are 49 village tracts in Tatkon Township and most of the rice growing village tracts were targeted in sampling frame. The four village tracts in which two are far from the main road and two are close to the main road, were selected for the study. The villages were selected with the assumption that if they are close to the main road, they have more chance to get extension services, irrigation water, market access, and up-to-date information.

The selected village tracts were Nyaungdone Aing, Kyauk Sa Yit Kone, Magyi Bin and Kyee Chaung. Sample respondents from each village tract were randomly selected and personally interviewed through structured interview schedule and a total of 157 respondents were involved in the study (Table 1).

Data collection and sources

For primary data collection, the questionnaire was tested in a pilot survey in January 2020. The initial structured interview schedule was refined after the pilot and the main survey was conducted in February to March, 2020.

Both quantitative and qualitative data were collected, including socio-economic characteristics such as cost and returns for monsoon rice cultivation, and nitrogen fertilizer management practices for monsoon rice cultivation such as type of N-fertilizer, amount used per acre, frequency and timing of fertilization per season of crop. Detailed costs (family labor involvement, hired labor cost and material input costs) and returns of paddy production were also collected to compare costs and benefits of proper and improper practices of N-fertilizer application. The secondary data were collected from published studies and official documents of Department of Agriculture (DoA), Ministry of Agriculture, Livestock and Irrigation (MOALI) and Central Statistical Organization (CSO).

Data analysis

Most of the nitrogen fertilizer recommendation for rice is to apply topdressing for three splits to be efficient nitrogen fertilization. The rate and timing of N fertilizer recommendations made by different agencies were described in Table 2. Therefore, the farmers who applied urea into three splits were grouped as proper N fertilization (PNF group) regardless of amout used per acre in this study. Then, the rest of samples who did not follow the recommendation of three splits N fertilizer application were grouped as improper N fertilization (INF group). There are varieties of different applications, which are improperly practiced by rice farmers are described in the result and discussion session.

Statistical Package for Social Science (SPSS) version 23 was used for data analysis. Descriptive analysis was used to identify nitrogen fertilizer application practices in monsoon rice production. Cost and return analysis was performed to compare costs and benefits of proper and improper practices of N-fertilizer application. Parameters estimated for cost and return analysis are shown in Table 3.

RESULTS AND DISCUSSION

Fertilizer applications practices in Tatkon Township

Urea, compound and ammonium sulphate were mostly used as N supplements for monsoon rice cultivation in the study area (Figure 2). Among them, 53% and 33% of the farmers who used urea applied N-fertilizer with two and three times split application, respectively. About 51% of the farmers who used compound fertilizer applied once a season of monsoon rice and the rest were using split application. Nitrogen fertilizer recommendation for rice may vary on soil fertility, targeted yield, rice varieties, age of rice and leaf color of rice. According to MOALI, nitrogen fertilizer recommendation for rice is to apply urea as topdressing three split applications: one-third bag (50Kg) of urea each time at 10-20 days after seeding/transplanting, tillering and panicle initiation stages. Two or three equal splits of N applied at sowing, tillering or anthesis increased growth attributes, dry matter accumulation and yield due to better crop nutrition and reduced N losses (Hafeez, 2013). Although there are various fertilizer recommendations, mostly are to apply three split applications for efficient nitrogen fertilization regardless of amount used of nitrogen per acre.

Different nitrogen fertilizers used by farmers

Table 4 shows the different types of fertilizers used by the farmers. Only one type of nitrogen fertilizer or various combinations of two or more types of nitrogen fertilizers were applied by the farmers in the study area. About 20% of farmers used only urea, 9% used only compound fertilizer, which may be various compositions of N-P2O5-K2O whatever available in market with their affordable price and 3% used only ammonium sulphate respectively for their monsoon rice cultivation. Combination of urea with compound was applied by 43% of the farmers and 5% applied combination of ammonium sulphate with compound. Although the recommedation is to apply straight fertilizer (urea, T-super and potash), farmers apply fertilizers based on their limited knowledge, budget constraints and availability in the market. Other combinations of urea with fertilizers such as compound, T-super, muriate of potash, ammonium sulphate, gypsum and organic fertilizer were also used by the farmers in the study area.

Table 4. Different nitrogen fertilizers used by farmers in the study area (n=157).

No.

Item

Frequency

Percent

1

Urea Only

31

19.75

2

Compound Only

18

11.46

3

Ammonium Sulphate Only

5

3.18

4

Urea+ Compound

71

45.22

5

Urea+ Muriate of Potash

3

1.91

6

Urea+ Ammonium Sulphate

3

1.91

7

Urea+ Organic fertilizer

2

1.27

8

Urea+ T-super

1

0.64

9

Ammonium Sulphate+ Compound

8

5.10

10

Ammonium Sulphate+ Organic fertilizer

1

0.64

11

Compound+ Organic fertilizer

1

0.64

12

Compound+ T-super

1

0.64

13

Urea+ Compound+ Muriate of Potash

2

1.27

14

Urea+ Compound+ Gypsum

3

1.91

15

Urea+ Compound+ T-super

3

1.91

16

Urea+ Ammonium Sulphate+ Compound

1

0.64

17

Urea+ Ammonium Sulphate+ T-super

1

0.64

18

Urea+ Ammonium Sulphate+ Muriate of Potash

1

0.64

19

Urea+ Compound+ Muriate of Potash+ Gypsum

1

0.64

 

Total Farmers

157

100.00

Split applications of nitrogen fertilizers

Kaushal (2010) stated that application of N into three splits at planting, tillering, and panicle initiation stages is most beneficial for achieving higher grain yield of modern rice varieties. Split applications of different nitrogen fertilizers by the farmers in the study area were shown in Table 5. Fertilizer recommendation made by the Department of Agriculture suggested to apply urea fertilizer as three split applications. However, less than a quarter or only 23.58% of the farmers followed the recommendation.

About 50.41% apply two split application of urea for monsoon rice cultivation and it can be said that half of the farmers followed the recommendation for urea fertilizer application closely. This finding coincided with the results from Thar, S.P. et.al., (2021). About 10.57% of farmers do not split urea application and they used only once during the rice cultivation. Although N fertilizer application is not recommended for the basal application, about 15.45% of farmers were applying it in basal.

Although compound fertilizer was not mentioned in official fertilizer recommendation for rice cultivation, one can use it as basal application instead of urea, triple-super phosphate and muriate of potash. It is not suggested to apply as topdressing or split application. Commercially available compound fertilizers can be observed with various combination of nutrients, N, P, K and S. The ratio of compound fertilizer which is mostly used by the sample farmers in the study area is 15:15:15. Some brands printed 15-15-15 as N-P-K ratio on fertilizer bags and some mentioned nothing.

Among the farmers, about 37.93% used compound fertilizer as the basal application. Other types of compound fertilizer applications were basal with one topdressing (2.44%), basal with two topdressings (9.48%) and basal with three topdressings (1.72%). Other types of compound fertilizer applying decisions were also observed such as three splits application without applying in basal with 7.76%, two splits with 17.24% and just one topdressing application with 12.93%. Generally compound fertilizer is more expesive than straight fertilizers. Therefore, proper application of compound fertilizer is very important to save the cost of production.

De Ferrante (1986) found that NH4 volatilization losses were larger in urea fertilizer than that of in ammonium sulphate used as a basal fertilizer for lowland rice cultivation. Ammonium sulphate fertilizers are generally available in two types: the straight form and the combination with a certain kind of herbicide. Although ammonium sulphate with herbicide was banned for import, farmers still love to use it. Nowadays, fertilizer companies distribute straight ammonium sulphate fertilizer and herbicide separately. The most popular way of application for ammonium sulphate is at the vegetative growth stage whenever they face with weed problem. Among the farmers who used ammonium sulphate, 65% of them applied as only one topdressing, 30% and 5% of farmers practice two splits and three splits topdressing, respectively. Ammonium sulfate and urea are equally effective for flooded rice production in Louisiana (Bufogle, 1998). Besides, market price of ammonium sulphate is cheaper than that of urea which is based on Kg of fertilizer. Similarly, if we estimate the price of two fertilizers based on Kg of N, the urea costed 0.91 USD/Kg N and the Ammonium Sulphate costed 0.81 USD/Kg of N&S during the time of survey. The ammonium sulphate available in Myanmar market consists of 21 percent Nitrogen and 24 percent of Sulphur. As Myanmar currency is depreciated dynamically, the current price of unrea in the Year 2022 costs 2.11 USD per Kg of Nitrogen and the ammonium sulphate costs 1.32 USD per Kg of Nitrogen and Sulphur together. Therefore, farmers should be aware of the benefits of using ammonium sulphate to minimize cost of production.

Time and amount of different nitrogen fertilizers application

Time and amount of different nitrogen fertilizers application by farmers were illustrated in Table 6. Average amount of urea applied by the farmers in the study area is 146 kg per hectare. As mentioned above, MOALI’s recommendation is to apply 124-185 kg of urea into three splits equally regardless of soil fertility status. Therefore, the average amount of urea applied per hectare was within the range of MOALI’s recommendation. The first topdressing of urea was applied at 26 days after sowing/broadcasting (DAS) of rice with the average amount of 63 kg urea per hectare. The second and third topdressing of urea were applied at 56 and 64 DAS of rice with the average amount of 66 and 65 kg urea per hectare respectively. Among all farmers, only 29 (23.58%) of them followed the recommendation of three split application of urea fertilizer (Figure 3.A).

Average amount of compound fertilizer applied was 136 kg/ha. The average amount of compound fertilizer for basal application was 105 kg/ha. The first topdressing was applied at 31 DAS of rice with the average amount of 70 kg/ha. The second and third topdressing of compound fertilizer were practiced at 51 and 69 DAS of rice with the average amount of 63 and 57 kg/ha, respectively (Figure 3. B). Ammonium sulphate fertilizer becomes popular among the farmers in these days with the reasons for lower price than that of urea and reducing volatilization losses. Average amount of ammonium sulphate applied was 112 kg/ha. The first topdressing of ammonium sulphate was applied at 24 DAS of rice with the average amount of 79 kg/ha. The second and third topdressing were applied at 58 and 60 DAS of rice with the average amount of 64 and 124 kg/ha respectively. Only one out of 20 ammonium sulphate users applied three splits (Figure 3.C).

Cost and return analysis of monsoon rice cultivation according to the farmers’ practice for N fertilization technique

As we mentioned above in the research method, the respondents were grouped into PNF group and INF group according to their N fertilization techniques. Total sample (n=157) was divided into two groups such as farmers with proper N fertilization technique (Proper N Fertilization Group, PNF group) where the size of sample is 29 and with improper N fertilization technique (Improper N Fertilization Group, INF group) where the size of sample is 128. The enterprise budget was calculated for monsoon rice cultivation according to the farmers’ practice for N fertilization technique in the study area. The gross benefit was computed by multiplying the yield and selling price of monsoon rice. The variable cost included materials cost, hired labor cost, machinery rental cost, family labor cost and interest on cash cost. The material costs included the cost of seed, farmyard manure, fertilizers, foliar and pesticides. Interest cost was estimated by assuming 9.6% per annum for five months which is the average production period of monsoon rice. The enterprise budget of monsoon rice cultivation according to the farmers’ practice for N fertilization technique was shown in Table 7. Yield and per unit production cost were significant at 10% level. The price received was significant at 5 percent level and material cost, interest on cash cost, total variable cash cost and total variable cost were significant at 1% level.

The yield of the PNF group was 3.831 MT/ha, and that of INF group was 3.591 MT/ha, which is significantly different at 10 percent level. The price received by PNF group was US$225/MT, and that of INF group was US$255/MT, which is significantly different at 5% level. The price received by INF group was higher because most of the farmers in that group grow better quality rice like Ayar Min and Paw San (Table 7). About one-third of INF group (34%) grow Ayar Min variety while more than half of PNF group (59%) were growing Sin Thukha variety which received less price than quality rice. It seems the farmers from PNF group were more traditional than the farmers in INF group. They grow the same variety for more than two decades. Probably, the farmers from INF group were more likely to be innovative. They tried to adopt new technologies such as quality rice varieties, and application of fertilizers according to their preferences which is different from recommended timing and rate. The most improper applications were putting urea fertilizer in basal and split application of compound fertilizer. The gross benefit was not statistically different between two farmer groups and that of INF group (US$899/ha) was higher than PNF group (US$868/ha) even yield of PNF group was better than INF group.

The material cost of PNF group was US$159/ha and that of the farmers with INF group was US$191/ha, which is significantly different at 1 percent level. This indicated the proper amount of fertilizer utilization costed less than that of other group. Both family labor and hired labor costs were higher in INF group than PNF group although the values were not statistically different. Interest on cash cost of PNF group was US$14/ha which is statistically significant at 1% level less than that of INF group (US$16 /ha). Total variable cash cost and total variable cost were also significantly different at 1 percent level between two farmer groups and the values are higher in INF group.

The hypothesis of the research was that PNF group would have lower material and operating cost and get more profit than INF group. The benefit cost ratio (BCR) or return per unit of capital for PNF group yielded 2.12 while that of INF group obtained1.96 although they were not statistically significant. Break-even price is marginal cost (MC) or per unit production cost (US$/MT) for monsoon rice production. MC for PNF group was US$124/MT and was significantly different at 10 percent level with that of INF group (US$141/MT). It can be clearly seen that the research findings proved the argument in hypothesis was true.

To reinforce the hypothesis of the study, partial budget analysis was carried out and the results were described in Table 9. The results revealed that there was no negative impact for proper utilization of N fertilizer and net benefit due to proper utilization of N fertilizer was US$115/ha.

CONCLUSION

Proper utilization of N fertilizer is very important to minimize cost of production for rice cultivation of Myanmar farmers. Various types of fertilizers were used by the farmers in the study area. Among them, mostly used N supplements for monsoon rice cultivation were urea, compound and ammonium sulphate. According to IFA’s Global 4R Nutrient Stewardship Concept, applying the Right Source of Nutrients, at the Right Rate, at the Right Time and in the Right Place, is important to achieve economic, social and environmental benefits. The fact that Myanmar is a net importer of all fertilizers, the prices of fertilizers keep increasing year by year. Nitrogen fertilizers are, therefore, very expensive inputs for most of the rice farmers and it is needed to allocate efficiently for rice cultivation. Minimizing operation cost is an alternative for increasing profitabality for rice farmers.

Farmers with proper N fertilization technique (PNF group) and with improper N fertilization technique (INF group) were categorized based on the right time of applying urea fertilizer in the study. The study revealed that only 18% of rice farmers was in PNF group and the rest was in INF group. Among all urea user farmers, one-third of them applied three splits, more than a half applied two splits, and the rest (14% applied only once a season. About half of the farmers who used compound fertilizer applied only once a season of monsoon rice and the rest were using split application. Fertilizer recommendation made by the Department of Agriculture suggested to apply urea fertilizer as three splits topdressing application and less than a quarter of farmers (23.58%) followed the recommendation. The ratio of compound fertilizer which is mostly used by the farmers in the study area has the N: P: K ratio of 15:15:15 and it is generally more expensive than straight fertilizers. Although, the information regarding the proper utilization of compound fertilizer is not available to the farmers, which is generally believed to be used only one time as a basal. Therefore, split application of compound as topdressing will add the cost of production unnecessarily. We can, therefore, conclude that more than one-third of the farmers used compound fertilizer properly as the basal application and the rest were applying improperly. Average amount of urea applied by the farmers in the study area is 146 kg/ha which falls between MOALI’s recommendation of 124-185 kg of urea per hectare. Average amount of compound fertilizer and ammonium sulphate applied were 136 kg/ha and 112 kg/ha, respectively.

According to the results of enterprise budgeting, BCR of PNF group was better than INF group although they are not statistically significant. Whereas, per unit production cost was also lower in PNF group, which leads to total variable cost was statistically significant between two farmer groups. Minimizing cost of production increases the profit and farmers can maximize their profitability by practicing nitrogen fertilization technique properly.

REFERENCES

Bufogle, A. Jr., P. K. Bollich, J. L. Kovar, C. W. Lindau & R. E. Macchiavellid (1998) Comparison of ammonium sulfate and urea as nitrogen sources in rice production, Journal of Plant Nutrition, 21:8, 1601-1614, DOI:10.1080/01904169809365507

De Ferrante, B., Van Der Vorm, P. & Van Diest, A. (1986) Comparative studies on the usefulness of ammonium sulphate and urea as fertilizers for lowland rice. Fertilizer Research 10, 119–133 (1986).

Eddie Funderburg. (2009) Nitrogen Losses from Urea. Noble Research Institute, May 2009.

Flanders Investment and Trade. (2020) Agriculture in Myanmar, Flanders Investment and Trade Market Survey, Report 2020.

Hafeez Ur Rehman, Shahzad M.A. Basra and A. Wahid.  (2013) Optimizing Nitrogen-split Application Time to Improve Dry Matter Accumulation and Yield in Dry Direct Seeded Rice, International Journal of Agriculture & Biology, ISSN Print: 1560–8530; ISSN Online: 1814–9596 12–240/2013/15–1–41–47 http://www.fspublishers.org

IFA. (2009). The global “4R” nutrient stewardship framework – developing fertilizer best management practices for delivering economic, social and environmental benefits, International Fertilizer Industry Association, Paris, France.

Kaushal A.K. (2010) Response of Levels and Split Application of Nitrogen in Green Manured Wetland Rice (Oryza sativa L.)

MOALI. (2016) Guidelines for Production, Postproduction, and Management of Rice in Rice-Rice Systems: A Case in Myanmar, Ministry of Agriculture, Livestock and Irrigation.

MOALI. (2019) Myanmar Agriculture at a Glance. Department of Planning, Ministry of Agriculture, Livestock and Irrigation.

Myanmar Rice Fedration (2021) Durations of rice varieties in Myanmar. Retrived from www.mrfriceportal.com/

Than, S.M., H.L. Lynn and A. Phyo. (2018) Ecoomics of Fertilizer Use Efficiecy for Selected Crops in Tatkon Township, Myamar Soil Fertility and Fertilizer Management Conference Proceedings, 2018.

Thar, S.P.; Farquharson, R.J.; Ramilan, T.; Coggins, S.; Chen, D. Recommended vs. Practice: Smallholder Fertilizer Decisions in Central Myanmar. Agriculture 2021, 11, 65. https://doi.org/10.3390/ agriculture11010065

World Bank. (2018) Fertilizer consumption rates for Asian countries. Retrived from http://data.worldbank.org/

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