Effects on Brassica napus L . Yield and Yield Components of Super Absorbent Polymer under Different Irrigation Regimes

For evaluation of the effects of super absorbent polymer under different irrigation regimes on the yield and yield components of Brassica napus L., a factorial experiment was carried out, based on randomized complete block design with four replicas. Treatments included super absorbent polymer (0, 1, 2, 3, 4 and 5 g/kg soil) and induced drought stress (irrigation at 25, 50 and 75 mm evaporation from class A pan). The experiment was conducted in pots with 5 kg of soil. Data analysis of variance showed the significant interaction effect between polymer and irrigation on the stem length, width and weight, the number of seeds per sheath, number of seeds per plant, the number of sterile and fertile sheath per plant, fertile sheath percentage (fertile sheath/ total sheath ×100), 1000 seeds weight, seed weight per plant, sheath weight per plant and the number of total sheath. The present study revealed that indifferent from the applied amounts of the super absorbent polymer, in all cases the measured characters have been more affected by induced drought stress.


Introduction
In many regions of the world, including Iran, water deficit stress is one of the most important factors that decrease agricultural crop production (Zahedi et al., 2009).Drought is the most significant factor restricting plant growth and crop productivity in the majority of agricultural fields of the world (Abedi and Pakniyat, 2010) and it negatively affects many plant processes, such as photosynthesis, transpiration, stomatal conductance, and metabolite accumulation (Ohashi et al., 2006).
Oil seed canola plant (Brassica napus L., rapeseed) is an important and worldwide agricultural crop grown primarily for its edible oil.This crop is mainly grown in rain fed areas, where water availability is one of the most important limiting factors affecting plant growth and development.Canola is generally considered to be more susceptible to drought.The yield is mainly affected by water shortages which occur during the stage from flowering to the end of the seed set (Din et al., 2011).The canola meal that remains after oil extraction is important as a protein source for the livestock feed industry (Jensen et al., 1996).Its oil is of premium quality with low erucic acid and glucosinolates contents.The yield of rapeseed is mainly affected by water shortages, which occur during the stage from flowering to the end of the seed set, because it is generally considered to be more susceptible to drought (Din et al., 2011).
The available water in soil is one of the most important factors of increasing crop yields (Ghooshchi et al., 2008).Improving the effectiveness of water application and optimum use of water source as one of the main axis of stable agriculture in dry and semi-dry regions is necessary.Super absorbent materials (SAMs) are hydrophilic polymer complexes that have potential to absorb large volumes of aqueous fluids within a short time and under stress conditions can hold the absorbed water (Akbal, 2004.).Super absorbent polymers may have great potential in restoration and reclamation of soil and storing water available for plant growth and production (Zhang et al., 2007).According to this basis, one of the ways to increase the water supply in soil is applying super absorbent polymers that supply water for crop roots (Pawlowski et al., 2009).Super absorbents are able to absorb and store water hundreds times of their dry weight (Abedi-Koupai and Asadkazemi, 2006).These polymers enhance the biological condition in water deficit stress by increasing the capacity of water storage in soil, reduction of wasting water and nutrition materials of soil (Sarvas et al., 2007).The application of super absorbent polymers has a significant impact in reducing drought stress effects and to improve plant yield and stability in agriculture production (Khadem et al., 2010.).The aim of this study was to evaluate the effect of five amounts of super absorbent materials (0, 1, 2, 3, 4 and 5 g/kg soil) and three levels of drought stress treatments (irrigation at 25 mm, 50 mm and 75 mm evaporation from pan class A) on yield and yield components of Brassica napus L.

Materials and methods
To evaluate effects of super absorbent polymer under different irrigation regimes on the yield and yield components of Brassica napus L., a factorial experiment was conducted based on randomized complete block design with four replicas, in year 2010.Treatments included super absorbents (0, 1, 2, 3, 4 and 5 g/kg soil) and drought stress (irrigation at 25 mm, 50 mm and 75 mm evaporation from class A pan).The experiment was conducted in pots with 5 kg of soil.From each plot five plants were harvested to determine the yield of seed.The following measurements were recorded from each of the plants: stem length (cm), stem diameter (mm), stem weight (g), the number of seeds per sheath, number of seeds per plant, seed weight per sheath (g) and seed weight per plant (g).
The dry weight was recorded after drying of samples in an oven at 70°C for 72 h.Seed and sheath were separated from leaves and stems before all plant parts were oven-dried at 70°C.At the end of growth stage, Soxhlet extraction was employed to determine the total oil concentration of the canola seed.In the Soxhlet procedure, 10 g of milled seeds were packed in a paper extraction thimble and oil was extracted by using 300 ml of petroleum benzene in a Soxhlet extractor, for 4 hours, and the solvent was then evaporated.Oils were filtered and dehydrated by using Whatman filters.Finally, oil content was determined by the following formula (Metcalf et al., 1996): Oil yield = Oil percentage × Seed yield Analysis of variance (ANOVA) on data was performed using the general linear model (GLM) procedure in the SAS 9.1 software.The Student-Newman Keul's test (SNK) was applied to compare treatment means using the MSTATC software.

Results and discussion
Interaction effects between super absorbent polymers and irrigation regimes on the stem length, stem width, stem weight, the number of seeds per sheath, the numbers of seeds per plant, number of fertile sheath per plant, fertile sheath percent, the number of sterile and total sheath, 1000 seeds weight, seed weight per plant, sheath weight per plant and oil percentage of seed were significant for (p≤0.01),too (p≤0.01)(Tab.1).Results from ANOVA analysis shows significant effect of super absorbents (p≤0.05) and drought stress (p≤0.01) on the sheath length.
Means comparison indicated that the longest sheath (5.01 cm) was obtained from control treatment, and the shortest sheath (4.45 cm) belonged to 1 g super absorbent polymer/ kg soil (Fig. 1).The use of 3 g polymer/kg soil produced the same sheath length as the application of 1 g polymer/kg soil.All treatments with super absorbent polymer produced shorter stems than control (Fig. 1-I).In irrigation treatments, the longest sheath (4.9 cm) was obtained from irrigation level at 25 mm evaporation from pan, while the shortest sheath (4.56 cm) belonged to irrigation at 75 mm evaporation.Increasing irrigation intervals from 25 to 75 mm evaporation caused shorten sheath, significantly different (Fig. 1-II).
The maximum stem width (3.2 mm) was observed at plants treated by 4 g polymer/kg soil and irrigation at 75 mm evaporation (Fig. 1-II, Fig. 2-II).The minimum stem width (1.7 mm) belonged to 4 g polymer/kg soil and irrigation at 50 mm evaporation likewise the irrigation at 50 mm evaporation and using 1 and 5 g polymer/kg soil (Fig.

2-II).
The highest stem weight (1.31 g) belonged to 3 g polymer/kg soil treatment and irrigation at 75 mm evaporation from pan.The lowest stem weight (0.53 g) was obtained from plants treated by 4 g polymer/kg soil under irrigation at 50mm evaporation, such as the stem weight of irrigation at 50 mm evaporation from pan and using 3 and 5 g polymer/kg soil (Fig. 3-III).370 Means comparison indicated that the longest stem (42.37 cm) was obtained from plants treated by 2 g polymer /kg soil and irrigation at 75 mm evaporation from pan. while the shortest stem (33.1 cm) belonged to plants treated with 4 g polymer/kg soil and irrigation at 50 mm evaporation from class A pan, and irrigation at 50 mm evaporation and 5 g polymer/kg soil (Fig. 1-II, Fig. 2-I).The obtained results show an ascending trend in stem length along with super absorbent polymers increase, in all irrigation regimes.Application of 2 g super absorbent polymers produced the highest stem length of Brassica napus in all irrigation regimes levels.The highest number of seeds per sheath (15.02) was obtained from using 3 g/kg soil of polymer and irrigation at 75 mm evaporation from pan, that similar irrigation after 75 mm evaporation from pan and by using 2 and 4 g/kg soil of polymer.The lowest number of seeds per sheath (8.7) belonged to 4 g/kg soil of polymer and irrigation at 50 mm evaporation from pan, similar with application 5g/kg soil of polymer and irrigation at 50 mm evaporation from pan (Fig.

2-IV).
The highest number of seeds per plant (292.4) was obtained from 2 g polymer/kg soil and irrigation at 75 mm evaporation from pan, similar with 3 g polymer/kg soil and irrigation at 75 mm evaporation from pan.The lowest number seed per plant (96.7) belonged to plants treated by 4 g polymer/kg soil and irrigated at 50 mm evaporation from pan, such as using 5 g polymer/kg soil and irrigation at 50 mm evaporation from pan.The same trends of stem length, here we obtained ascending trend in number of seeds per plant along with super absorbent polymer increase, in all irrigation regimes.Application of 2 g of super absorbent polymers produced the highest number of seeds per plant of Brassica napus in irrigation regime levels.
The maximum number of fertile sheath (19.7) belonged to irrigation at 75 mm evaporation from pan and using 4 g polymer/kg soil as same as using 2 and 3 g polymer/kg soil along with irrigation at 50 mm evaporation.The minimum number of fertile sheath per plant (11.18) belonged to irrigation at 50 mm evaporation and using 4 g polymer/kg soil, likewise in case of the application of 5 g polymer/kg soil in this above irrigation regime.Results showed ascending trend in fertile sheath along with super absorbent polymer increase, in all irrigation regimes (Fig. 3-I).
Like fertile sheath number, the maximum fertile sheath percent (96.4%) belonged to irrigation at 75 mm evaporation from pan and using 4 g polymer/kg soil as same as using 2 and 3 g polymer/kg soil along with irrigation at 50 mm evaporation.The minimum fertile sheath percent (71.3%) belonged to irrigation at 50 mm evaporation and using 4 g polymer/kg soil as same as 5 g polymer/kg soil in this irrigation (Fig. 3-II).
The maximum number of sterile sheath (2.4) was occurred at 3 g polymer/kg soil and irrigation at 75 mm evaporation from pan, that it was the same with 4 g polymer/kg soil and irrigation at 75 mm evaporation from pan.The minimum number of sterile sheath (0.25) belonged to irrigation at 50 mm evaporation from pan and by using 5 g/kg soil of polymer, that similar by 4 g polymer/kg soil and irrigation at 50 mm evaporation (Fig.

3-III).
The maximum number of total sheath per plant (21.95) was obtained from irrigation at 75 mm evaporation from pan and using 4 g polymer/kg soil, such as with 2 and 3 g/kg and irrigation at 75 mm evaporation.The minimum number of total sheath (11.59) belonged to the usage of 4 g polymer/kg soil irrigated at 50 mm evaporation from pan, similar to 5 g polymer/kg soil and irrigation at 50 mm evaporation.Here we obtained ascending trend in sheath total along with super absorbent polymer increase, in all irrigation regimes, the sheath total at 5 g of polymer showed a decline in comparison with others (Fig. 3-IV).
The greatest 1000 seeds weight (6.55 g) belonged to plants treated with 2 g polymer/kg soil and irrigated at 75 mm evaporation from pan.And the lowest amounts of 1000 seeds weight (1.74 g) was obtained from plants treated by 4 g polymer/kg soil and irrigation at 50 mm evaporation from pan, that it had no different with application of 3 g polymer/kg soil in this irrigation (Fig. 4-I).
The greatest seed weight per plant (1.1 g) belonged to plants treated with 3 g polymer/kg soil and irrigation at 75 mm evaporation from pan.It had no different with 2 and 4 g polymer/kg soil irrigated at 75 mm evaporation from pan.The lowest amounts of seed weight per plant (0.3 g) was observed in plants treated by 4 g polymer/kg soil and irrigated at 50 mm evaporation as same as seed weight of using 5 g polymer/kg soil and irrigation at 50 mm evaporation from pan (Fig. 4-II).
The maximum sheath weight per plant (2.78 g) belonged to 2 g polymer/kg soil and irrigation at 75 mm evaporation, that it was similar to 3 and 4 g polymer/kg soil and irrigation at 75 mm evaporation.The minimum sheath weight per plant (0.57 g) belonged to 4 g polymer/kg soil and irrigation at 50 mm evaporation, same with 5 g polymer/kg soil and irrigation at 50 mm evaporation (Fig.

4-III).
The maximum percentage of seed oil (34.8%) belonged to plants treated by 3 g polymer/kg soil and irrigation at 75 mm evaporation from pan, that it was the same with oil percent of 2 and 4 g polymer/kg soil and irrigation at 75 mm evaporation.The minimum percentage of seed oil (18.7%) was obtained from 4 g polymer/kg soil and irrigation at 50 mm evaporation from pan, that it was similar to 5 g polymer/kg soil in this irrigation.Despite of increasing oil percent in the lower polymer treatments, the oil percentage of 4 and 5 g polymer/kg soil was declined rather than 2 and 3 g polymer/kg soil (Fig. 4-IV).

Discussion
Super absorbent polymers are able to store water in an effective way and under stress condition gives it to the plant.These materials prevent water and nutrition materials leaching, therefore increase the yield of the plant (Tohidi-Moghadam et al., 2009).Abraham and Rajasekharan Pillai (1995) reported that hydrophilic polymers application significantly reduced the amount of ammonium leaching from the soil structure.Researches from Yazdani et al. (2007) on soybean showed that application of super absorbent polymers under drought stress increased grain yield and the total dry weight of soybean plants.The application of super absorbent polymers has a significant impact in reducing drought stress effects and to improve plant yield and stability in agriculture production (Khadem et al., 2010).Khadem et al. (2010) also showed that adding super absorbent polymers can linearly increase 1000-seed weight of corn and soybean crops, respectively.Hayat and Ali (2004) also found that polymer effect on yield parameters helps the increase crop yield.Razmjoo et al. (2008) and Baghalian et al. (2011) reported that drought stress caused a significant reduction in plant height, stem weight and flower yield of Matricaria chamomilla.Moreover, drought stress significantly reduces the plant height, stem dry weight, flower diameter, flower fresh and dry weight in marigold based on reports of Abdul-Wasea and Khalid (2010).Singh and Ramesh (2000) also reported that water deficit stress reduced the oil yield of rosemary on a hectare basis, but oil yield on a plant fresh weight basis did not appear to be affected.Baghalian et al. (2011) reported that drought stress caused a significant reduction in yield of Matricaria chamomilla.Afsharmanesh (2009) stated the significant effect of drought stress on reduction of fresh and dry weight in sorghum and alfalfa.Drought stress lead to weak transfer of mineral nutrient from soil to plant (Hopkins, 2004) and causes significant reduction in dry weight in comparison with control plants (Iqbal et al., 2005.).Moazen Ghamsari et al. (2009) also reported the increase in function with application of 300 and 200 kg super absorbent in hectare.Probably using super absorbent caused to increase in number and weight of 1000seeds that cause increase in function of the seed in mentioned attendance.Nazarli et al. (2010) reported high 100-seed weight, resulting from more irrigation, was probably due to the availability of adequate soil moisture and assimilates from source to sink seed formation and seed ripping stages.Application of polymer tended to increase 100-seed weight of sunflower compared to the control (without polymer).

Conclusions
The greatest 1000 seeds weight (6.55 g) and the maximum numbers of total sheath per plant (20.25) were observed at plants treated by 3 g polymer/kg soil and irrigation at 75 mm evaporation.The maximum number of fertile sheath (19.7) and the highest fertile sheath percentage (96.4%)belonged to 4 g polymer/kg soil and irrigation at 75 mm evaporation.The minimum 1000 seeds weight (1.74 g), the number of total (11.5),fertile sheath (11.18) and fertile sheath percentage (71.3%)was correlated with the irrigation at 50 mm evaporation at application of 4 g of polymer/kg soil.The maximum oil percentage (34.8%)resulted at the treatment using 3 g polymer/kg soil and irrigation at 75 mm evaporation from pan.

Fig. 1 .
Fig. 1.Means comparison of sheath length of Brassica napus L. treated with varying amounts of super absorbent (I) under different Irrigation regimes (II).The same letters show non-significant differences

Fig. 4 .
Fig. 4. Means comparisons of sheath on 1000 seeds weight (I), seed weight per plant (II), sheath weight per plant (III) and oil percent (IV) at different levels of super absorbent polymer and drought stress Analysis of variance of super absorbent polymer and irrigation effects on the yield and yield components of Brassica napus L.