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Sustainability 2014, 6(3), 1153-1162; doi:10.3390/su6031153

Assessment of Rice Inbred Lines and Hybrids under Low Fertilizer Levels in Senegal
Ghislain Kanfany 1, Raafat El-Namaky 1,*, Kabirou Ndiaye 1, Karim Traore 1 and Rodomiro Ortiz 2
Africa Rice Center, Sahel Station, B.P. 96, Saint Louis 46100, Senegal
Department of Plant Breeding, Swedish University of Agricultural Sciences (SLU), Box 101, SE 23053 Alnarp, Sweden
Author to whom correspondence should be addressed; Tel.: +221-77-385-9666; Fax: +221-33-962-6491.
Received: 12 November 2013; in revised form: 14 February 2014 / Accepted: 18 February 2014 / Published: 28 February 2014


: This research was conducted at the Africa Rice Sahel Regional Station (near Saint Louis, Senegal) during two wet seasons (i.e., July to November) in 2010 and 2011 with the aim of assessing the performances of introduced hybrid cultivars along with an inbred check cultivar under low input fertilizer levels. The five treatments used in this study were (a) the control (without any fertilizer application), (b) 37.5–4.4–8.3 kg N–P–K ha−1, (c) half of recommend application in Senegal (75–8.75–16.5 kg N–P–K ha−1), (d) 112.5–13.3–24.8 kg N–P–K ha−1, and (e) the recommended application in the country (150–17.5–33 kg N–P–K ha−1). There were significant year and cultivar effects for all traits. The fertilizer levels affected significantly most traits except panicle length and 1000-grain weight. The year × fertilizer level and year × cultivar interactions were significant for most traits, but the fertilizer level × cultivar and year × fertilizer level × cultivar interactions were not significant. Days to maturity, plant height, panicle per m2, and grain yield increased with increasing fertilizer levels during the two wet seasons. The grain yield of rice hybrids (bred by the International Rice Research Institute) was not significantly higher than that of the check cultivar widely grown in Senegal. The assessment of other rice hybrid germplasm showing more adaptability to low fertilizer levels will facilitate further hybrid cultivar development in Africa.
Africa; hybrid vigor; low input; N-P-K; nutrient-use-efficiency

1. Introduction

Sub-Saharan African farmers considered fertilizer to be costly or unaffordable, particularly when fertilizer prices increased following the removal of subsidies. Fertilizers are more expensive in most of sub-Saharan Africa than in any other continent mainly due to the lack of efficient fertilizer market infrastructure and poor transport network [1]. Many countries were forced to reduce fertilizer imports or expansion plans. Senegal is currently one of the largest rice consumers in West Africa. Self-sufficiency rate of rice is as low as 20% of the total demand. Two main ecologies of rice exist in Senegal. The irrigated rice where the average yield is 6.5 t at farmers “level while under the upland ecologies farmers are getting less than 2 t per ha. Under irrigated conditions, the production cost is heavy due the use of pesticide, fertilizers, and non-adapted credit systems. The main abiotic constraints are problem soils like salinity, acidity, and iron toxicity for lowland and drought for upland ecology. Consumers’ preference varies from region to region and it is also based on the recipes. In the rice-growing environment, whole rice is preferred, while, in big towns, consumers prefer broken. Many farmers had to decrease their P and K inputs to offset production expenses, and some governments had to reduce fertilizer subsidies.

Fertilizers are very important inputs to intensify rice production elsewhere. The profitability of rice production systems depends on grain yield and amounts of inputs [2]. The appropriate fertilizer input allows the cultivars to achieve high grain yields, thereby, bringing profits to farmers.

Labor costs and the purchasing of synthetic fertilizers are often the largest investment made by rice farmer elsewhere. Enhanced fertilizer-use-efficiency can therefore benefit rice farmers. It can be improved by using cultivars with high nutrient-use-efficiency or nutrient management options that take into account the indigenous soil supply and an attainable grain yield based on climate, farmers’ knowledge regarding crop husbandry, and capital availability.

The aim of this experiment was to assess the efficiency of using synthetic fertilizers by high-yielding rice inbred and hybrid cultivars during the wet season in a location at Senegal’s Sahel. Such an assessment will allow identifying suitable rice hybrids for low-input agro-systems.

2. Materials and Methods

The field trials were at Africa Rice Sahel Regional Station, near Saint Louis (Senegal) during the season (i.e., July–December) of 2010 and 2011. The rice germplasm included in both years were hybrids bred by the International Rice Research Institute [3], and the inbred cultivar Sahel 108 as check as it is widely grown by farmers in Senegal.

Five fertilizer treatments (F) were used in this study. They were F0 (or control; i.e., without any fertilizer application) F1 (37.5–4.4–8.3 kg N–P–K ha−1) F2 or half of recommend fertilizer application in Senegal (75–8.75–16.5 kg N–P–K ha−1), F3 (112.5–13.3–24.8 kg N-P-K ha−1) and F4 or the recommended application in the country (150–17.5–33 kg N–P–K ha−1).

The hybrids and the inbred cultivar used as check were sown in a wet nursery. Seedlings were transplanted 25 days after sowing, using a single plant per hill and distancing each by 20 cm. The experimental layout was a randomized complete block design (RCBD) with three replications. Soil characteristics were measured before crop establishment and fertilizer application (Table 1). The minimum and maximum temperature of 2010 and 2011, in Saint Louis Senegal, are shown in Figure 1.

Table 1. Chemical soil analysis of plot fields in Saint Louis, Senegal during two wet seasons.
Table 1. Chemical soil analysis of plot fields in Saint Louis, Senegal during two wet seasons.
(g cm−3)
(dS m−1)
(g kg−1)
Soluble Cation
Soil texture

Db = Bulk density; PH = alkalinity or acidity; Ec = electric conductivity; CEC = cation exchange capacity; C/N = means the ratio between carbon and nitrogen.

Figure 1. Minimum and maximum temperatures (°C) at Saint Louis (Senegal), in 2010 and 2011.
Figure 1. Minimum and maximum temperatures (°C) at Saint Louis (Senegal), in 2010 and 2011.
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Days to 50% flowering, plant height (cm), panicle length (cm), spikelet sterility (%), 1000-grain weight, number of panicle per m2, and grain yield (t ha−1) were recorded according to the Standard Evaluation System for rice [3]. Grain quality traits such as total milling recovery, whole percentage, and alkali spreading value (ASV) were also recorded after harvesting F0, F2 and F4 plots in the 2010 and 2011 wet seasons. The method used for ASV involved the visual observation of the degree of dispersion of grains of the milled rice after their immersion in 1.7% KOH [4]. Alkali digestion determines indirectly the gelatinization temperature (GT). A low ASV corresponds to a high GT, and, conversely, a high ASV corresponds to a low GT. Rice with low amylose content has often a soft gel, low ASV, and high GT [5]. SAS version 9.2 [6] was used for analyzing the data. The main sources of variation were years, cultivars and fertilizer levels, as well as their 2- and 3-level factor interactions.

3. Results

The year affected significantly (p < 0.05) most traits except spikelet sterility, while cultivars differed significantly (p < 0.01) for all traits (Table 2). The effect of fertilizer levels was significant (p < 0.05) for days to 50% flowering, plant height, panicle per m2, spikelet sterility, and grain yield. The year × fertilizer interaction was significant (p < 0.05) for most traits except panicle per m2 and 1000-grain weight, while there was a significant year × cultivar interaction for most traits but panicle length (cm). The remaining 2- and 3-level interactions were non-significant (p > 0.05).

Table 2. Analysis of Main square for the effect of year and fertilizer levels on traits assesses in 13 rice hybrids and inbred cultivar grown during the 2010 and 2011 wet seasons in Senegal.
Table 2. Analysis of Main square for the effect of year and fertilizer levels on traits assesses in 13 rice hybrids and inbred cultivar grown during the 2010 and 2011 wet seasons in Senegal.
Source of variationDF Flowering (days after sowing)Plant height (cm)Panicle length (cm)Number of panicles per m2Spikelet sterility (%)1000-grain weight (g)Grain yield (t ha−1)
Year (Y)125.7 *46158.1 ***2601.3 ***1228719.3 ***134.3521.3 ***6200.0 ***
Fertilizer (F)469.1 ***688.9 ***1.2170985.4 ***152.6 *1.967.6 ***
Cultivar (C)13325.1 ***784.7 ***22.5 ***26087.8 ***110.3 **10.9 **1.8 **
Y × F482.0 ***141.1 **10.5 *3181.1162.9 **4.849.0 **
Y × C1351.9 ***140.5 ***5.035649.6 ***121.4 **20.8 ***2.1 **
F × C524.424.02.02080.
Y × F × C523.510.81.63293.931.53.10.5
Error 2806.5728.333.32479.738.84.410.65

Degrees of Freedom *, ** and *** indicate that the source of variation was significant at p ≤ 0.05, 0.01 and 0.001, respectively.

The wet season in 2010 was significantly (p < 0.05) more benign than in 2011, as noted by the trait means (Table 3). Plant height, days to 50% flowering, panicles per m2, spikelet fertility, and grain yield increased significantly (p < 0.05) when fertilizer levels went up (Table 3). Plots without fertilizer showed early days to 50% flowering (around 90 days) during both years while spikelet sterility decreased when using above half of the recommended fertilizer level for Senegal in 2010 (Figure 2).

Table 3. Mean performance across years and for each fertilizer levels across both years.
Table 3. Mean performance across years and for each fertilizer levels across both years.
Flowering (days after sowing)Plant height (cm)Panicle length (cm)Panicles per mSterility (%)1000-grain weight (g)Grain yield (t/ha)
193.2 a93.8 a25 a437 a22.2426.4 a5.94 a
291.6 b82.8 b20 b328 b23.3724.2 b5.09 b
p-value0.0486<0.0001NS <0.0001NS<0.0001<0.0001
Fertilizer levels
F089.5 c84.51 d22.4321 d23.5 a25.04.41 d
F191.0 b86.63 c22.5355 c23.7 a25.25.04 c
F293.0 a88.75 b22.6389 b23.8 a25.45.52 b
F394.0 a89.5 a,b22.7416 a22.2 a,b25.36.10 a,b
F494.5 a91.5 a22.7431 a20.6 b25.26.42 a

Standard error of differences; NS indicates non-significant differences (p > 0.05); a, b, c, d means with same letter are not significantly different (p > 0.05).

Figure 2. Response across rice cultivars to increasing fertilizer levels of days to flowering, (a) plant height, (b) panicle length, (c) spikelet sterility, (d) panicle m−2, and (e) grain yield in the 2010 and 2011 wet seasons in Saint Louis, Senegal.
Figure 2. Response across rice cultivars to increasing fertilizer levels of days to flowering, (a) plant height, (b) panicle length, (c) spikelet sterility, (d) panicle m−2, and (e) grain yield in the 2010 and 2011 wet seasons in Saint Louis, Senegal.
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There were significant differences (p < 0.05) for most traits among the hybrids and between them and the check cultivar Sahel 108 (Table 4). IR86167H (97 days) had the longest period of vegetative growth, while the IRR1138 was the earliest for days to 50% flowering during the wet season of both years. The inbred cultivar Sahel 108 exhibited the shortest stature (74 cm), while the tallest (91.7 cm) were IR81954H and IR83212H. IR80228H had the largest panicle (24 cm) and the shortest panicle (21 cm) was noted in Sahel 108, which produced the highest number of panicles per m2 (466). The highest and lowest percentages of spikelet sterility were found in hybrids IR83212H and IR 81954H, respectively. IR81950H had heavy grains (26.6 g for 1000 grains) that weighed significantly above those of Sahel 108 (24.7 for 1000 grains), while the lightest grains were found in IR81955H (24.4 g for 1000 grains). IR80228H showed the highest yielding hybrid (5.9 t ha−1), but its grain yield was not significantly different than that of Sahel 108 (5.9 t ha−1).

Table 4. Performance of 13 rice hybrids and inbred cultivar across fertilizer levels and wet seasons.
Table 4. Performance of 13 rice hybrids and inbred cultivar across fertilizer levels and wet seasons.
Cultivars Days to 50 % floweringPlant height (cm)Panicle length (cm)Panicle per m2Sterility (%)1000- grain weight (g)Grain yield (t ha−1)
IR80228H94 c,d,e87.5 b24.0 a352 d,e20.83 b,c24.9 a.b5.9 a
IR80814H89 g,f80.6 c21.9 d,e,f385 b,c,d,e21.91 a.b,c25.6 ab5.1 b
IR81950H96 a.b83.9 b,c23.5 a.b,c393 b,c,d20.86 b,c26.6 a5.2 b
IR81954H95 a.b,c91.7 a22.7 a.b,c,d,e372 c,d,e19.01 c25.9 a.b5.7 a.b
IR81955H93 e80.7 c23.1 a.b,c,d423 a.b24.26 a.b24.4 b5.7 a.b
IR82391H90 f83.9 b,c22.2 c,d,e,f385 b,c,d,e24.50 a.b25.3 a.b5.3 a.b
IR83212H94 c,d,e91.8 a22.9 a.b,c,d405 b,c26.35 a24.5 b5.2 b
IR84711H95 b,c,d81.4 c22.6 a.b,c,d,e385 b,c,d,e24.40 a.b25.3 a.b5.5 a.b
IR84741H89 g,f81.4 c22.5 b,c,d,e369 c,d,e23.36 a.b,c25.3 a.b5.7 a.b
IR85466H96 a.b85.8 b22.4 c,d,e358 c,d,e21.18 a.b,c24.8 b5.5 a.b
IR85471H87 h76.3 d21.4 e,f392 b,c,d22.91 a.b,c25.6 a.b5.6 a.b
IR86167H97 a87.1 b22.8 a.b,c,d,e340 e23.53 a.b,c25.7 a.b5.6 a.b
IRR113888 g,h81.1 c23.9 a.b348 d,e22.31 a.b,c25.6 a.b5.4 a.b
Sahel 10893 d,e74.1 d21.0 f446 a23.88 a.b,c24.7 b5.8 a.b
p-value<0.0001 <0.0001 <0.0001 <0.0001 0.0007 0.0035 0.0011

Standard error of differences; a–h means with same letter are not significantly different (p > 0.05).

Average of grain yield for hybrid varieties under different fertilizer levels present in (Table 5). Generally grain yield increased with increasing of fertilizer levels for most hybrids and check variety. In the same time, no significant interactions observed between hybrid varieties different fertilizer levels. Grain quality traits did not follow any trend according to fertilizer levels (Table 6). The inbred check cultivar Sahel 108 had the best milling recovery and whole grain percentage, while IRR1138 exhibited the best ASV at zero and intermediate fertilizer levels.

Table 5. Grain yield average of 13 rice hybrids and inbred cultivar under different fertilizer levels.
Table 5. Grain yield average of 13 rice hybrids and inbred cultivar under different fertilizer levels.
Sahel 1084.244.895.686.667.65

S.E.D. : 0.466; p-value: 0.0011.

Table 6. Grain quality of 13 rice hybrids and inbred cultivars after using fertilizer levels: control without fertilizer application (F0), half-recommended application (F2) and recommended application (F4) after the 2010 and 2011 wet seasons in Saint Louis, Senegal.
Table 6. Grain quality of 13 rice hybrids and inbred cultivars after using fertilizer levels: control without fertilizer application (F0), half-recommended application (F2) and recommended application (F4) after the 2010 and 2011 wet seasons in Saint Louis, Senegal.
Total milling recovery (%)Whole grain (%)Alkali spreading value
Sahel 10864.4064.0863.6354.3054.4349.002.332.503.16
S.E.D. 1.4364.890.291

Standard error of differences.

4. Discussion

Grain yield decreased in most rice cultivars when lowering fertilizer use in the wet seasons of 2010 and 2011. An increase of fertilizer levels significantly improves growth, grain and straw yields of rice. This result also confirms that fertilizer (N, P and K) is essential for increasing rice grain yields [7,8,9]. It promotes rapid growth and increases leaf size, spikelet number per panicle, percentage of filled spikelet in each panicle and grain protein content [10,11,12,13,14] also indicated that the grain yield of most rice hybrids significantly increased when N-fertilizer went up to 180 kg ha−1. Lin et al. [15,16,17,18,19,20,21,22] found that the system of rice intensification (SRI) can significantly reduce N-fertilizer use due to planting hybrid seed at low density.

High fertilizer levels also extended the vegetative growth. Plants were taller in the first year than in the second year, which suggest that climate and affect plant height. Although Yadav [16] indicated that nitrogen levels did not affect significantly plant height at all stages of rice growth, an increased use of fertilizers led to tall plants in this experiment, which supports previous findings by Van Hach [17].

Years affected significantly panicle length, which was bigger in 2010 than in 2011. This could be due to the wider range between day and night temperatures in 2011 (Figure 1). An increase on fertilizer levels led to having more panicles per m2, thereby suggesting that nitrogen seems to be effective for stimulating tillering. Increasing fertilizer levels did not lead to heavy grains because the sink capacity (i.e., spikelet number) was high in the cultivars during both years. These findings agreed with previous research [12,18,19,20]. A high number of panicles per m2 and the number of filled grains per panicle will increase grain yields.

The grain yield advantage of IRRI-bred hybrids was not significantly above than that of the inbred check cultivar in Senegal. Their grain yield was higher in 2010 than in 2011, when there was a three-week flood due to heavy rains. Newly bred hybrid rice cultivars have high physiological efficiency due to its vigorous root system, great sink size, large leaf area index during grain filling, and wide adaptability to various environments, including saline soils [21].

Testing new rice hybrids under low fertilizer levels may facilitate identify suitable germplasm showing adaptability to the low-input farming systems of Senegal. Nonetheless, plant breeders should keep in mind that the potential impacts of rice hybrids in sub-Saharan Africa will be influenced by other factors beyond the genotype, environment, and crop husbandry. They are related to conducive policy for adopting this seed technology, working input markets for seeds and fertilizers, institutional arrangements throughout the value chain (including extension systems), and social demographics influenced by end-users (i.e., farmers, millers and consumers).

5. Conclusions

More studies need to be conducted to propose a specific formula of fertilizer per variety or group of varieties knowing that they respond differently. The same studies need to be conducted in areas with problem soils to combine tolerant varieties and fertilizer application to increase the average yield across ecologies.


This research work was funded by Africa Rice Center (AfricaRice). The authors thank Howida El-Habet for technical soil analysis.

Author Contributions

Ghislain Kanfany, Raafat El-Namaky, Kabirou Ndiaye and Karim Traore participated in the research and did data analysis, Raafat El-Namaky and Rodomiro Ortiz planed, analyzed results, and wrote this article.

Conflicts of Interest

The authors declare no conflict of interest


  1. Fairhurst, T. Handbook for Integrated Soil Fertility Management; Africa Soil Health Consortium: Wallingford, UK, 2012. [Google Scholar]
  2. Khuang, T.Q.; Huan, T.T.; van Hach, C. Study on fertilizer rates for getting maximum grain yield and profitability of rice production. Omonrice 2008, 16, 93–99. [Google Scholar]
  3. International Rice Research Institute (IRRI). Standard Evaluation System for Rice, 4th ed.; IRRI: Los Baños, Philippines, 1996. [Google Scholar]
  4. Little, R.R.; Hilder, G.B.; Dawson, E.H. Differential effect of dilute alkali on 25 varieties of milled white rice. Cereal Chem. 1958, 35, 111–126. [Google Scholar]
  5. Tan, Y.F.; Li, J.X.; Yu, S.B.; Xing, Y.Z.; Xu, G.C. The three important traits for cooking and eating quality of rice grains are controlled by a single locus in a rice hybrid, Shanyou 63. Theor. Appl. Genet. 1999, 99, 642–648. [Google Scholar] [CrossRef]
  6. Statistical Analysis System (SAS). SAS/STAT® 9.2 User’s Guide; SAS Institute Inc.: Cary, NC, USA, 2004. [Google Scholar]
  7. Alam, M.M.; Hassanuzzaman, M.; Nahar, K. Tiller dynamics of three irrigated rice varieties under varying phosphorus levels. Am.–Eurasian J Agron. 2009, 2, 89–94. [Google Scholar]
  8. Alinajati Sisie, S.; Mirshekari, B. Effect of phosphorus fertilization and seed bio fertilization on harvest index and phosphorus use efficiency of wheat cultivars. J. Food Agr. Environ. 2011, 9, 388–397. [Google Scholar]
  9. Dastan, S.; Siavoshi, M.; Zakavi, D.; Ghanbaria-Malidarreh, A.; Yadi, R.; Ghorbannia Delavar, E.; Nasiri, A.R. Application of nitrogen and silicon rates on morphological and chemical lodging related characteristics in rice (Oryza sativa L.) at north of Iran. J. Agr. Sci. 2012, 4. [Google Scholar] [CrossRef]
  10. Balasubramanian, V.; Morales, A.C.; Cruz, R.T.; Abdulrachman, S. On-farm adaptation of knowledge-intensive nitrogen management technologies for rice systems. Nutr. Cycl. Agroecosys. 1999, 53, 59–69. [Google Scholar]
  11. Peng, S.B.; Garcia, F.V.; Laza, R.C.; Sanico, A.L.; Visperas, R.M.; Cassman, K.G. Increased N-use efficiency using a chlorophyll meter on high yielding irrigated rice. Field Crop. Res. 1996, 47, 243–252. [Google Scholar] [CrossRef]
  12. Xu, H.G.; Zhou, H.J. Effects of nitrogen fertilizer application on the growth and development of rice following wheat at different stages. J. Hebei Agr. Univ. 1999, 22, 5–9. [Google Scholar]
  13. Yang, W.H.; Peng, S.; Huang, J.; Sanico, A.L.; Buresh, R.J.; Witt, C. Using leaf color charts to estimate leaf nitrogen status of rice. Agron. J. 2003, 95, 212–217. [Google Scholar]
  14. Zayed, B.A.; El-Ekhtyar, A.M.; El Abd, A.A.; Badawi, M.A. Response of hybrid and inbred rice varieties to various nitrogen levels under saline soil conditions. J. Agr. Sci. Mansoura Univ. 2006, 31, 7497–7509. [Google Scholar]
  15. Lin, X.Q.; Zhu, D.F.; Chen, H.Z.; Cheng, S.H.; Uphoff, N. Effect of plant density and nitrogen fertilizer rates on grain yield and nitrogen uptake of hybrid rice (Oryza sativa L.). J. Agr. Biotechnol. Sustain. Dev. 2009, 1, 44–53. [Google Scholar]
  16. Yadav, P.B.; Panwar, C.S.; Somappa, J.; Srivastava, K.; Singh, D.K. Yield and quality performance of basmati genotypes under varying nitrogen levels. Plant Archives 2012, 12, 815–818. [Google Scholar]
  17. Van Hach, C.; Nam, N.T. Responses of some promising high-yielding rice varieties to nitrogen fertilizer. Omonrice 2006, 14, 78–91. [Google Scholar]
  18. Lai, M.H.; Chen, C.C.; Kuo, Y.C.; Lu, H.Y.; Chern, C.G.; Li, C.P.; Tseng, T.H. The relationship between grain productivity and nitrogen-fertilizer rate of different nitrogen rates on grain yield and components in rice. J. Agr. Res. China 1996, 45, 203–217. [Google Scholar]
  19. Metwally, T.F.; Sedeek, S.E.M.; Abdel khalik, A.F.; El-Rewiny, I.M.; Metwali, E.M.R. Genetic behaviour of some rice (Oryza sativa L.) genotypes under different treatments of nitrogen levels. Am.-Eurasian J. Agr.Environ. Sci. 2010, 8, 27–34. [Google Scholar]
  20. Singh, T.; Shivay, Y.S.; Singh, S. Effect of date of transplanting and nitrogen on productivity and nitrogen use indices in hybrid and non-hybrid aromatic rice. Acta Agr. Hung. 2004, 52, 245–252. [Google Scholar] [CrossRef]
  21. Sun, Y.Y.; Sun, Y.J.; Chen, L.; Xu, H.; Ma, J. Effects of different sowing dates and low-light stress at heading stage on the physiological characteristics and grain yield of hybrid rice. Ying Yong Sheng Tai Xue Bao 2012, 23, 2737–2744. [Google Scholar]
  22. Yongjian, S.; Ma, J.; Sun, Y.; Xu, H.; Yang, Z.; Liu, S.; Jia, X.; Zheng, H. The effects of different water and nitrogen managements on yield and nitrogen use efficiency in hybrid rice of China. Field Crop. Res. 2012, 127, 85–98. [Google Scholar] [CrossRef]
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