IPI International Potash Institute
IPI International Potash Institute

Research Findings: e-ifc No. 20, June 2009

Preliminary Field Observations on the Response of Wheat and Barley to High Rates of K Fertilization in Rainfed and Irrigated Regions in Lebanon

Al-Zubaidi, A., A. Alameddine, and I. Bashour1
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(1) Faculty of Agricultural and Food Sciences, American University of Beirut, Lebanon. Corresponding author: ib02@aub.edu.lb

Introduction
The role of potassium (K) as an essential nutrient for agricultural crops is well established. Uptake of potassium is frequently as high as or even higher than that of nitrogen (N) (Mengel and Kirkby, 2001). About 50 enzymes, including those responsible for energy transfer and the formation of sugars, starch and proteins are activated by potassium so that its supply to the plant and its cellular concentration within the plant are of major importance (Krauss, 1997; Drast, 1992).

Adequate potassium nutrition results in superior quality cereal plants because of improved efficiency of photosynthesis, increased resistance to some diseases, and greater water use efficiency. It also helps maintain a satisfactory balance between carbohydrates and protein and, in addition, strengthens cereal straw and favors grain filling.

Map of Lebanon with the experimental sites.
Map of Lebanon with the experimental sites.

Older literature from Lebanon (Ryan and Hamze, 1981) indicates a lack of response of cereal crops to added potassium fertilizers on Bekaa clay soils containing 200 mg available K/kg soil. Recent investigations on K availability in Lebanese soils, however, has provided evidence of a possible positive response to K fertilization in Akkar soils, which are low in K content (Al-Zubaidi et al., 2008a and 2008b). Recently, Darwish et al. (2007) also reported that in clay soils, potato responded to K application even when soil testing showed an available value close to 300 mg K/kg soil. Similarly, Al-Zubaidi (2003) observed that high doses of potassium were found to be beneficial for barley in some Iraqi soils.

There is limited information regarding the response of cereals to high rates of potassium fertilization in different Lebanese soils. The purpose of this field work was therefore to test the response of wheat to potassium application in irrigated soils of the Beqaa valley and the response of wheat and barley in rainfed soils of the Akkar plain in Lebanon (see map).

     
  Table 1. Soil properties at AREC farm, Beqaa Valley.  
  Parameter Unit Value  
  EC dS/m 0.28  
  pH - 7.67  
  CEC cmol/kg 31.0  
  CaCO3 % 29.7  
  OM % 2.6  
  Exch. cations      
  Ca mg/kg 5,670  
  Mg mg/kg 274  
  Texture class - Clay  
  Potassium      
  H2O-K mg/kg 4.5  
  Exch.-K mg/kg 575  
  Acid-K mg/kg 1,460  
  K-saturation % 7.7  
         

Field Trial No. 1: Response of irrigated wheat in the Beqaa Valley
A field experiment was conducted in the Beqaa area at the American Research and Educational Center (AREC) of the American University of Beirut (AUB), 80 km east of Beirut. Some physical and chemical properties of the soil (Table 1) were determined according to the methods described by Richards (1954). Different potassium forms (water-soluble: H2O-K; potassium extracted by NH4OAC: Exch-K; and potassium extracted by nitric acid: Acid-K) were determined by the methods described by Pratt (1965). The concentration of potassium in all extracts was measured by flame photometry.

The trial was carried out during 2006- 2007. Each of the plots was 100 m2. The fertilization treatments were as indicated in Table 2. At harvest, the grain was collected, weighed and yields of treatments compared.

         
  Table 2. Fertilization treatments applied in both locations.  
  Treatment N-P2O5-K2O Fertilization  
    kg/ha  
  Control 0 0  
  N 170-0-0 810 ammonium sulphate  
  NP 170-170-0 810 ammonium sulphate + 350 superphosphate  
  NPK1 170-170-170 1,000 compound fertilizer (17-17-17)  
  NPK2 170-170-340 1,000 compound fertilizer (17-17-17) + 340 of potassium sulphate  
  NPK3 170-170-510 1,000 compound fertilizer (17-17-17) + 680 of potassium sulphate  
  Note: In addition to these nutrients, 100 kg N/ha was applied at the tillering/elongation stage in all treatments.  
     

Results
The yield of wheat (grain) in kg/ha in different treatments is shown in Table 3.

     
  Table 3. Yield of wheat (kg/ha) in different treatments, AREC farm.  
    Treatment Yield    
      kg/ha    
    Control 344    
    N 659    
    NP 1,496    
    NPK1 1,437    
    NPK2 1,888    
    NPK3 2,171    
     

The data shows that there was a marked increase in the grain yield of wheat in the treatments which received N-P or NP- K in comparison with the control and N only treatment. The increase in the yield of wheat was observed, in particular, in treatments NPK2 and NPK3, which received double and triple doses of potassium fertilizers (340 and 510 kg K2O/ha, respectively). This shows that applying high rates of potassium could be beneficial for wheat production in this region. We suggest that using 17-17-17 compound fertilizer (1,000 kg/ha) for wheat may not supply enough potassium for maximum yield. It is also worth mentioning that the analysis of soil samples after harvest showed that the application of K fertilizer increased the amounts of water-soluble K, and exchangeable-K as well as in the ratio of exch-K/exch. Ca+Mg, indicating that the application of K-fertilizer had a positive residual effect on soil potassium (results not shown).

The results of a second experiment which were repeated during 2007-2008 at AREC farm confirmed the observations made during 2006-2007: there was a clear response of wheat to potassium fertilizer application in treatments NPK2 and NPK3, which received double and triple doses of potassium as compared to NPK1 treatment (Table 4). These findings also clearly indicate that the affect on yield was brought about by an increase in the 1,000 grain weight.

         
  Table 4. Yield of wheat in different treatment for the year 2007-2008, AREC farm.  
  Treatment Yield 1,000 grain weight  
    mt/ha gr  
  NPK1 4.40 171  
  NPK2 5.07 181  
  NPK3 5.27 212  
         

Field trial No. 2: Response of rainfed wheat and barley at Akkar Plain
The response of high K fertilization under rainfed conditions was carried out in a field trial on rainfed farmers' fields in Arida, Akkar plain, North Lebanon during 2006-2007. The fertilization treatments were the same as those shown in Table 2. The area of each plot was one dunam (1,000 m2). Soil properties are outlined in Table 5.

         
  Table 5. Soil properties at Arida, Akkar plain.  
  Parameter Unit Value  
  EC dS/m 0.34  
  pH - 8.0  
  CEC cmol/kg 29.0  
  CaCO3 % 3.75  
  OM % 2.65  
  Texture class - Sandy clay loam  
  Exch. cations      
  Ca mg/kg 3,560  
  Mg mg/kg 793  
  K mg/kg 45  
         

Results
This field observation was carried out on a large scale (one dunum for each treatment) in the farmers' fields. The relative yields were used for comparing the effect of each treatment with that of the control as indicated in Table 6. The results show that, in general, wheat responded much more to fertilization than barley. The greatest response of both crops was to treatment NPK2 (170 kg N, 170 kg P2O5 and 340 kg K2O per ha) which received a double dose of potassium as compared to that of NPK1. In the case of wheat, the yield was 6.71 mt/ha (2 mt/ha or 43.4 per cent greater than the control) and for barley 4.64 mt/ha (only 0.6 mt/ha or 15 per cent greater than the control). At the highest rate of potassium application, treatment NPK3, the yield response of both wheat and barley declined, probably because of the nutrient imbalance introduced in this treatment. It was also observed that the wheat and barley straw in treatments NPK2 and NPK3 were taller and thicker than in the other treatments.

               
  Table 6. Yields of rainfed wheat and barley crops, Arida, Akkar.  
  Treatment No Yield   Relative Yield  
    Wheat Barley   Wheat Barley  
    mt/ha   %  
  Control 4.68 4.03   100.0 100.0  
  N 5.30 4.10   113.3 101.7  
  NP 5.59 4.23   119.4 104.5  
  NPK1 5.98 4.13   127.8 102.5  
  NPK2 6.71 4.64   143.4 115.2  
  NPK3 5.66 4.35   121.0 107.9  
               

Conclusions
A positive response to doubling the rate of K fertilization was observed at both the Beqaa and Akkar Plain field trials. The increase in yield for wheat in the two field trials ranged between 20-26 per cent when comparing yield of NP to NPK2 treatments. For barley, however, the increase in yield was about 10 per cent when comparing NP to NPK2 treatments.

Under present international prices of wheat and barley (US$180-200/mt), expenditure on such an increase in potassium use may not be economically viable. But should international prices of cereals increase, such as occurred in 2008 to US$600-800/mt, then farmers should give due attention to the positive response of large applications of potash fertilization for cereals in Lebanese soils.

Acknowledgments
Special thanks go to the University Research Board (URB) at the American University of Beirut; The Institute of International Education's Scholar Rescue Fund (SRF); and the International Potash Institute (IPI) for their support to this work.

Papers from Lebanon
The following publications, papers and presentations from Lebanon appear on the IPI website:

1. Evaluations of K Availability in Selected Soils from Lebanon. Al-Zubaidi, S. Yanni, and I. Bashour. 2008. e-ifc No. 15, March 2008.
View paper.

2. Fertigation and Conventional Potassium Application to Field Grown Potato in Lebanon: Perspective to Enhance Efficiency. Darwish, T., T. Atallah, N. Khatib, and F. Karam. 2004. Presented at the Potassium and Fertigation Development in WANA, Marrakesh, Morocco.
View paper.

3. Fertigation Potentials in the Near East Region. Bashour, I., and M. Nimah. IPI Regional Workshop on Potassium and Fertigation Development in West Asia and North Africa, Rabat, Morocco, 24-28 November 2004.
View paper.

4. Balanced Fertilization in WANA Region. Krauss, A. Presented at the IPI-NCARTT Regional Workshop on Potassium and Water Management in West Asia and North Africa, 5-8 November 2001, Amman, Jordan.
View paper.

References

  • Al-Zubaidi, A. 2001. Potassium status in Iraqi soils. In: Proceedings of the Regional Workshop on Potassium and Water Management in West Asia and North Africa. Johnston, A.E. (ed.). International Potash Institute, Horgen, Switzerland. p.129-124. See IPI website
  • Al-Zubaidi A., S. Yanni, and I. Bashour. 2008a. Evaluations of K availability in selected soils from Lebanon. e-ifc No. 15, March 2008. International Potash Institute, Horgen, Switzerland.
    See IPI website.
  • Al-Zubaidi A., S. Yanni, and I. Bashour. 2008b. Potassium status in Lebanese soils. National Center for Scientific Research Journal, Volume 9, No 1.
  • Darwish, T., T. Atallah, N. Khatib, and F. Karam. 2007. Fertigation and conventional potassium application to field grown potato in Lebanon: Perspective to enhance efficiency. p.141-153. In: Proceedings of the Regional Workshop of the International Potash Institute held at Rabat, Morocco, 24-28 November 2004. Badraoui, M., R. Bouabid and A. Ait Houssa (ed.). International Potash Institute, Horgen, Switzerland. See IPI website
  • Drast, B.C. 1992. Development of the potash fertilizer industry. Potash Review, subject 12, 12th suite. International Potash Institute, Horgen, Switzerland.
  • Krauss, A. 1997. Potassium, the forgotten nutrient in West Asia and North Africa. Accomplishment and Future Challenges in Dryland Soil Fertility Research in Mediterranean Area. Ryan, J. (ed.). ICARDA.
  • Mengel, K., and E.A. Kirkby. 2001. Principles of Plant Nutrition. 5th edition. Kluwer Academic Publishers, Dordrecht.
  • Pratt, P.F. 1965. Potassium. In: C.A. Black et al. (ed.) Methods of soil analysis, Part 2, Agronomy 9:1023-1031. Amer. Sc. of Agron. Madison, Wis.
  • Richards, L.A. 1954. Diagnosis and improvement of saline and alkali soils. USDA Handbook No 60. U.S. Government Printing Office, Washington D.C. (www.ars.usda.gov).
  • Ryan, J., and M. Hamza. 1981. Soil fertility studies in Lebanon: a perspective. Lebanese science bulletin, 3(2):93-104.
The paper "Preliminary Field Observations on the Response of Wheat and Barley to High Rates of K Fertilization in Rainfed and Irrigated Regions in Lebanon" also appears at:
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