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Chilean journal of agricultural research

versión On-line ISSN 0718-5839

Chilean J. Agric. Res. vol.72 no.3 Chillán set. 2012 

Agricultural Research 72(3) July - September 2012


Allelopathic Effects of Sunflower Residue on Growth of Rice and Subsequent Wheat Crop

Efectos Alelopáticos de Residuos de Girasol sobre el Crecimiento de Arroz y Cultivo de Trigo Subsecuente

Uzma Bashir1*, Arshad Javaid1, and Rukhsana Bajwa1

1University of the Punjab, Institute of Agricultural Sciences, Quaid-e-Azam Campus Lahore 54590, Pakistan. "Corresponding author (

Sunflower (Helianthus annuus L.) is a well known allelopathic plant species. However, Pakistani farmers generally incorporate the sunflower residue in the soil with the aim to enhance soil fertility and organic matter. Field experiments were, therefore, carried out to evaluate the effect of sunflower residue incorporation on growth and yield of rice (Oryza sativa L.) and subsequent wheat (Triticum aestivum L.) crop. For rice crop, there were four treatments viz. control, sunflower residue incorporation (RI), NPK fertilizers, and NPK+RI. Two rice varieties (Basmati Pak and Basmati Super) were cultivated. Incorporation of sunflower residue markedly reduced plant growth and yield in 'Basmati Pak'. There was 34% reduction in yield of this variety due to RI. 'Basmati Super' was tolerant to sunflower allelopathy, where the effect of RI was generally insignificant on plant growth and grain yield. Two commonly cultivated varieties of wheat (Inqalab 91 and Punjab 96) were sown in the same plots after harvesting the rice, without any addition of either RI or NPK. In 'Punjab 96', the effect of RI or RI+NPK was insignificant on grain yield. In contrast, in 'Inqalab 91', RI in combination with NPK fertilizers significantly reduced the grain yield by 41% as compared to NPK alone. The present study concluded that rice 'Basmati Super' and wheat 'Punjab 96' are suitable for cultivation under sunflower allelopathic stress.

Key words: Allelopathy, genotypic tolerance, Oryza sativa, Helianthus annuus, Triticum aestivum.

El girasol (Helianthus annuus L.) es una planta alelopática bien conocida. Sin embargo, los agricultores de Paquistán generalmente incorporan el residuo de girasol en el suelo con el objetivo de mejorar la fertilidad y la materia orgánica del suelo. Los experimentos de campo se realizaron para evaluar el efecto de la incorporation de residuos de girasol en el crecimiento y production de arroz (Oryza sativa L.) y trigo (Triticum aestivum L.) subsecuente. Para el cultivo de arroz hubo cuatro tratamientos viz. Control, incorporation de residuo de girasol (RI), fertilizantes NPK, y NPK+RI. Se cultivaron dos variedades de arroz (Basmati Pak y Basmati Super). La incorporation de residuo de girasol redujo marcadamente crecimiento de planta y production en 'Basmati Pak'. Hubo una reduction de 34% en production de esta variedad debida a RI. 'Basmati Super' fue tolerante a alelopatía del girasol, siendo el efecto de RI generalmente insignificante en crecimiento de planta y production de grano. Dos variedades comúnmente cultivadas de trigo (Inqalab 91 y Punjab 96) se sembraron en las mismas parcelas después de cosechar el arroz, sin adicion de RI o NPK. En 'Punjab 96', el efecto de RI o RI+NPK fue insignificante en rendimiento de grano. En contraste, en 'Inqalab 91', RI+NPK redujo significativamente la production de grano, 41% comparado con NPK solo. El presente estudio concluyo que el arroz 'Basmati Super' y trigo 'Punjab 96' son apropiados para cultivo bajo estrés alelopático de girasol.

Palabras clave: Alelopatía, tolerancia genotípica, Oryza sativa, Helianthus annuus, Triticum aestivum.

The potential impacts of allelopathy on agriculture have been described during last 40 years. Many crops have been reported to be allelopathic towards other crops grown either simultaneously or subsequently (Chattopadhyay, 1995; Kawata et al., 1996; Khanh et al., 2005). Consequently, it has been suggested that crops with allelopathic effect on the other crops should not be followed by susceptible ones (Kausar, 1999). Roth et al. (2000) observed that Sorghum bicolor (L.) Moench frequently reduced grain yield of wheat (Triticum aestivum L.) when the crops are grown in rotation. Oleszek and Jurzysta (1987) reported wheat seed germination and seedling growth were suppressed by water and alcohol extracts of alfalfa (Medicago sativa L.) roots. This phenomenon has also been reported in other crops like corn (Zea mays L.) and oat (Avena sativa L.) (Nielsen et al., 1960; Al-Tawaha and Odat, 2010), rice (Oryza sativa L.) (Hisashi, 2004; Javaid et al., 2008) and cotton (Gossypium hirsutum L.) (Ioannis et al., 2005). The allelopathic effects are selective, depending upon the concentrations and residue type, either inhibitory or stimulatory to the growth of companion or subsequent crops or weeds (Mushtaq et al., 2003; Cheema et al., 2004; Javaid et al., 2007).

Sunflower (Helianthus annuus L.) is recognized as an important crop in several areas of Pakistan due to suitability of the crop to local agroclimatic conditions, its importance as source of edible oil and protein, resistance to drought and its short duration (Kamal and Bano, 2009). However, yields of some crops following sunflower are lower than normal, possibly because of inadequate nutrition and chemical inhibition (Kamal and Bano, 2008). More than 200 natural allelopathic compounds have been isolated from different cultivars of sunflower (Kamal and Bano, 2009). Sunflower leaf extracts caused reduction in radical and hypocotyl length of mustard seedling (Wardle et al., 1991; Bogatek et al., 2006). Sedigheh et al. (2010) observed that sunflower parts significantly inhibit the germination of Solanum nigrum L. Being a short duration and economically important crop, sunflower is cultivated twice a year (spring and autumn) in Pakistan. However, generally sunflower is cultivated on larger scale in spring than in autumn season. Spring sown sunflower is cultivated during March-April and is harvested in June in Pakistan. Generally, it is followed by rice cultivation. In past farmers used to burn sunflower residue after harvest. Nowadays, sunflower residue is generally incorporated in the soil with the idea that it will add to the organic matter and fertility of the soil. The allelochemicals released from crop residues in the soil are likely to cause adverse effects on the proceeding crops, and such detrimental interactions cannot be over looked in rice-wheat cropping system in the country. The present study was, therefore, designed to investigate the effect of incorporation of sunflower residue on growth and yield of two rice varieties and two wheat varieties grown thereafter.


Incorporation of sunflower residue
Certified seeds of sunflower var. Hysun 33 (Monsanto Pakistan (Pvt) Ltd.), commonly cultivated in Pakistan, were sown on ridges in 2 x 2 m plots at a depth of 1 cm in March 2007. Seeds were planted with inter-row and inter-plant spacing of 75 and 30 cm, respectively. A basal dose of 120 kg N ha-1 as urea, 90 kg P2O5 ha-1 as triple super phosphate and 60 kg K2O ha-1 as potassium sulfate was applied in each plot. Plots were irrigated as recommended for sunflower. After 90 d of sowing, mature sunflower plants were decapitated. Remaining vegetative parts were uprooted, cut into small pieces of 3-5 cm, mixed into the field soil up to the depth of 15-18 cm and left till the cultivation of rice crop in July.

Cultivation of rice
Two commonly grown rice varieties ('Basmati Pak' and 'Basmati Super') were selected for field study. Rice nursery was raised during June in field plots of 4 x 6 m. Plots were supplied with recommended fertilizer doses and regular irrigation and hand weeding was carried out as and when required. Forty days old seedlings of the two selected rice varieties were transferred to field plots with inter and intra row spacing of 22 cm. There were four treatments: Control, sunflower residue incorporation (RI), NPK fertilizers, and RI+NPK. The recommended dose of chemical fertilizers was: 120 kg N ha-1 as urea, 60 kg P2O5 ha-1 as triple super phosphate, and 60 kg K2O ha-1 as sulfate of potash. Plants were harvested at vegetative, flowering, and ripening stages. Data regarding number of tillers per plant, shoot length and dry weight, and root dry weight were recorded at all the three harvest stages. Similarly, data regarding panicle length, grain yield and 100 grains weight were recorded at ripening stage.

Cultivation of subsequent wheat crop
After the harvesting of rice crop, two wheat varieties ('Inqalab 91' and 'Punjab 96') were sown in same plots without any addition of NPK fertilizers or sunlower residue. Data regarding various plant growth and yield parameters were recorded at three growth stages similar to that of rice crop.

Statistical analysis
All the data were analyzed by ANOVA followed by Tukey's test to separate the treatment means using computer software SPSS 11.


Effect of sunflower residue incorporation on growth and yield of rice
The effect of incorporation of sunlower residue and NPK fertilizers on vegetative growth of rice is presented in Table 1. In rice 'Basmati Pak', sunflower RI insignificantly reduced the number of tillers and shoot length at all three growth stages. In contrast, RI significantly suppressed shoot biomass at vegetative stage. The effect of RI was insignificant on root biomass at all three growth stages. Rice 'Basmati Super' was comparatively tolerant to sunlower residue amendment. The effect was insignificant on all studied plant growth parameters in this variety. NPK fertilizers significantly enhanced shoot dry biomass at vegetative growth stage in 'Basmati Pak'. In general, various plant growth parameters were markedly suppressed when sunlower residue was incorporated in combination with NPK fertilizers as compared to NPK fertilizers alone. The effect was more pronounced in 'Basmati Pak' than in 'Basmati Super'.

Table 1. Effect of sunflower residue incorporation (RI) on plant vegetative growth of two rice varieties at different growth stages.

In a column, values with different letters show significant difference as determined by Tukey's Test at P ≤ 0.05.

The effect of sunlower RI and NPK fertilizers on various reproductive growth parameters of the two tested rice varieties is illustrated in Figure 1. In rice 'Basmati Pak', the highest panicle length was recorded in NPK fertilizers treatment. Incorporation of sunlower residue significantly reduced the panicle length as compared to control and other treatments. Addition of NPK fertilizers in combination with sunlower residues increased the panicle length significantly in this rice variety. In rice 'Basmati Super', the effect of various treatments on panicle length was insignificant as compared to control (Figure 1A). Grain yield in rice 'Basmati Pak' was reduced by 34% due to the application of sunlower residue. Application of NPK fertilizers markedly alleviated the allelopathic stressof sunlower residue. The effect of residue on grain yield of rice 'Basmati Super' was insignificant (Figure 1B). The effect of different treatments of sunlower residue and NPK fertilizers on 100 grain weight of the two rice varieties was insignificant (Figure 1C).

Figure 1. Effect of sunflower residue incorporation (RI) on yield of two rice varieties.

Vertical bars show standard errors of means of three replicates. Values with different letters show significant difference according to Tukey's test at P ≤ 0.05.

Effect of sunflower residue incorporation on growth and yield of wheat
Data regarding the effect of sunlower RI and NPK fertilizers on vegetative growth of wheat is summarized in Table 2. Incorporation of sunlower residue insignificantly reduced number of tillers at vegetative growth stages in 'Inqalab 91'. RI exhibited insignificant effect on shoot length in 'Inqalab 91' at all growth stages. However, residue application significantly reduced shoot length at lowering and ripening stages in 'Punjab 96'. Residue incorporation significantly declined shoot dry weight at vegetative stage in 'Inqalab 91'. In contrast, the effect of RI on this plant growth parameter of 'Punjab 96' was insignificant at all three growth stages. Although RI adversely affected root growth, this effect was statistically insignificant on root dry biomass in both wheat varieties. Application of NPK fertilizers generally enhanced root and shoot growth. The effect was more pronounced and significant at flowering and ripening stages than at vegetative growth stage. Wheat 'Punjab 96' showed more susceptibility to sunlower RI in the presence of NPK fertilizers as compared to 'Inqalab 91'. There was insignificant effect of RI and NPK on number of tillers at all three growth stages in 'Inqalab 91' as compared to NPK fertilizers alone. In contrast, in 'Punjab 96', a significant reduction in tillering was recorded at lowering and ripening stages. Shoot dry weight was significantly reduced at flowering stage only in 'Inqalab 91' while residue incorporation showed insignificantly effect on this plant growth parameter in 'Punjab 96'. Root dry weight was significantly reduced at lowering stage in 'Punjab 96', due to combined application of sunlower residue and NPK as compared to NPK fertilizers alone.

Table 2. Effect of sunflower residue incorporation (RI) on plant vegetative growth of two wheat varieties cultivated in the same field after harvesting the rice crop.

In a column, values with different letters show significant difference as determined by Tukey's Test at P ≤ 0.05.

Data about the effect of sunlower RI and NPK fertilizers on various reproductive growth parameters of the two tested wheat varieties is shown in Figure 2. In both wheat varieties, the effect of sunlower RI was insignificant on ear length and grain yield and 100 grains weight (Figures 2A-C). NPK fertilizers alone significantly enhanced ear length in both wheat varieties as compared to control. Ear length was significantly reduced in both wheat varieties in combined application RI+NPK as compared to NPK fertilizers alone (Figure 2A). Grain yield was significantly enhanced by 39% and 31% in 'Inqalab 91' and 'Punjab 96', respectively, due to NPK fertilizers as compared to control. However, there was significant decrease of 41% in grain yield in 'Inqalab 91' when RI+NPK was applied as compared to NPK fertilizers alone. By contrast, in 'Punjab 96', there was insignificant difference in grain yield between NPK fertilizers alone and RI+NPK treatments (Figure 2B).

Figure 2. Effect of sunflower residue incorporation (RI) on yield of two wheat varieties cultivated in the same field after harvesting rice crop.

Vertical bars show standard errors of means of three replicates. Values with different letters show significant difference according to Tukey's test at P ≤ 0.05.


n the present study, two varieties of rice were cultivated in field soil amended with sunflower residue with or without application of recommended dose of NPK fertilizers. In rice 'Basmati Pak', sunflower RI significantly reduced shoot biomass and grain yield. Earlier, Morris and Parrish (1992) observed declined yield of winter wheat when sunlower residues were tilled into the soil. Similarly, Batish et al. (2002) reported decreased germination, growth, and yield of four summer season crops namely millet, sorghum, corn, and clusterbean, when grown in fields containing sunflower residues. Recently, Ashrafi et al. (2008) found that soil incorporation of fresh sunlower roots and both roots and shoots reduced wild barley (Hordeum spontaneum K. Koch.) germination, plant height and weight when compared with a no-residue control. The reduced plant growth in soil amended with sunlower RI could be attributed to the presence of allelochemicals in different parts of sunlower. Many terpenes and phenols have been reported in different sunflower cultivars (Ghafar et al., 2001; Macias et al., 2004). These allelochemicals are often water-soluble substances which are released into the surrounding environment through root exudation, leaching and decomposition of plant residues (Ashrafi et al., 2008), and adversely affect germination and growth of other plants (Batish et al., 2002).

After harvesting rice crop, two varieties of wheat ('Inqalab 91' and 'Punjab 96') were cultivated in same plots without any further addition of sunlower residue or NPK fertilizers. The negative effect of the RI on root and shoot growth as well as grain yield of the two wheat varieties was not as much pronounced as was in case of the two rice varieties. It could be due to degradation of allelochemicals in the soil by physical, chemical, and microbial processes (Katase, 1981; Hess et al., 1992; Vidal and Bauman, 1992). However, in treatments where RI+NPK was applied in previous rice crop, the response of the two wheat varieties was different. In case of 'Inqalab 91', a significant reduction in grain yield was recorded in RI+NPK application as compared to NPK fertilizers alone. In contrast, in 'Punjab 96', the effect was insignificant on grain yield. Since, generally NPK fertilizers are applied in rice crop, thus wheat 'Punjab 96' is more suitable for cultivation under sunlower allelopathic stress than 'Inqalab 91'.

The results of the present study clearly demonstrate the genotypic variation in growth and yield response of different varieties of rice and wheat to allelopathic stress caused by decomposing sunlower residue. Between the two rice varieties, 'Basmati Super' was comparatively more tolerant to allelopathic stress of sunlower residue than 'Basmati Pak'. Similarly, the adverse effect of RI on grain yield was more pronounced on wheat 'Inqalab 91' than on yield in 'Punjab 96'. Earlier, Javaid et al. (2007) reported genotypic variation in rice cultivars against allelopathic stress of Cyperus rotundus L. They reported that rice 'IRRI-8' and 'IRRI-Fine' were more tolerant to phytotoxicity of C. rotundus than various Basmati varieties viz. 'Pak Basmati', 'Basmati Super', and 'Basmati 385'. Genotypic variation in tolerance to allelopathy has also been reported in other crop-allelopathic plants interactions (Table 3). This unequal susceptibility of various rice varieties to the sunlower extracts could be due to inherent differences in physiological and morphological characteristics of various genotypes involved (Macias et al., 1992).

Table 3: Genotypic variation in tolerance to allelopathic stress.


The present study concludes that the adverse effects of sunlower residue incorporation on rice and subsequent wheat crop can be reduced by cultivation of allelopathic tolerant varieties. Rice 'Basmati Super' is more suitable than 'Basmati Pak' for cultivation under allelopathic stress of sunlower followed by cultivation of wheat 'Punjab 96' as grain yield in these varieties is not significantly affected due to sunlower residue incorporation in combination with NPK fertilizers.



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Received: 4 October 2011.
Accepted: 13 June 2012.

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