Influence of primed seed and varying seed rate on growth and productivity of soybean (Glycine max L.) under different planting techniques

Soybean is a high value crop with multiple food, feed and industrial uses. Edible oil, soymilk and its products, bakery products, antibiotic and fresh green beans are some of its major uses. Soybean has potential to play an important role in crop diversification in the Punjab. Despite of its importance soybean crop cover low area in Punjab and its production is negligible. Agro-climatic conditions, planting methods and seed rate plays substantial role in the adaptation of the crop in the cropping system. So, to enhance the area and production of soybean crop different techniques are required which improves the germination of the seeds like pre sowing treatments with certain chemicals or growth regulators which improves the germination of the seeds and provide better medium for their growth.
       
Seed priming is a process of adjusting the germination process by controlling the moisture content, the seed is taken through the first biochemical processes within the initial stages of germination and bringing the seed closer to the point of germination without protrusion of radical. The process involves advancing the seed to an equal stage of the germination process, to enable fast and uniform emergence when planted. There are several benefits to seed priming and they include faster speed of emergence of primed seeds, widen the temperature range of survival in the seeds for example in cold and wet or under hot, conditions. Priming of seeds also improves uniformity to optimise harvesting efficiency, increases vigour for fast and strong plant development and increases yield potential of the crop plants. Seed priming has been commonly used to reduce the time between seed sowing and seedling emergence and to synchronize emergence (Parera and Cantliffe, 1994).
       
Optimum planting technique and seed rate influence the growth and productivity of the soybean crop. The bed planting can save considerable amount of irrigation water and maximize water productivity (Dhindwal et al., 2006). Also bed planting reduces seed rate and provides favourable environment for the growth and development of the soybean (Ram and Kler, 2007). Optimum seed rate provide better resource utilization ability to the crop plants. Seed yield increases with increment in seed rate but only up to certain extent. Keeping in view the inter-plant competition for nutrition, sunlight, moisture and aeration it is essential to find out fair combination of suitable method of sowing with optimum seed rate to achieve maximum yield of soybean. So, the study was planned with the objective to estimate the optimum seed rate under different planting methods for realising higher yield of soybean.

Experimental design
 
The experiment was set up in factorial split plot design with four replications consisting of two planting techniques (flat and bed planting method) and two seed priming treatments (non-primed seeds and 100 ppm GA₃ primed seeds) in main plot and three seed levels ( 50, 62.5 and 75 kg ha^-1) in sub plot. Sowing was done by pora method in flat sown soybean with proper row to row and plant to plant spacing of 45 and 5 cm, respectively. A fine seed bed was prepared by giving two cultivations with tractor drawn cultivator followed by planking and beds were prepared with spacing of 67.5 cm apart by using maize bed planter. Two rows per bed were sown with pora method. Soybean seeds were soaked in primer (100 ppm GA₃) for seed priming treatments and after two hours it was taken out and dried under shade and immediately used for sowing. Dry seeds were used as non primed seed. Application of fertilizer was same for all the treatments i.e. recommended dose of nitrogen (32 kg ha^-1) applied through urea and phosphorus (80 kg ha^-1 P₂O₅) as single super phosphate was as a starter dose at the time of sowing.Other crop management practices were as per the local package of practices of PAU (Package of practices for crops of Punjab, 2015-16). The following observations were recorded after 30 days of sowing till harvesting of the crop.
 
Emergence count
 
The number of seeds emerged was recorded daily up to 9^th days after sowing. The emerged seedlings were counted from one metre row length from two fixed selected places in each plot (Rathod et al., 2016).
 
Plant height
 
Periodic plant height of five tagged plants per plot was recorded at 30 DAS till at harvest of the crop. The measurements were taken from the base of main stem to the last fully opened leaf. The mean plant height was computed at various stages and expressed in cm (Ram et al., 2011).
 
Dry matter accumulation
 
Five random plants were selected to calculate the DMA of the plants from each plot periodically at 30 days interval. The whole above ground portion of the plants was taken and sun dried. The sun dried samples were then oven dried at 60°C ± 2°C and expressed in g plant^-1 (Ram et al., 2011).
 
Leaf area index
 
LAI was determined by Sun Scan probe v1.02R (DELTA-A Devices) at 30, 60 and 90 DAS. The observations were taken at random from four places in each plot between 12:00 noon to 12:30 pm.
 
Photosynthetically active radiation interception
 
PARI was measured between 12:00 noon and 2:00 pm, on clear sunny day at 30, 60 and 90 days after sowing with LINE Quantum Sensor Photometer. The incoming and outgoing radiations on top of the canopy and radiation penetration at the ground surface below the crop canopy were measured. The observations were taken at random from two places in each plot. The per cent interception was calculated as under:

        

                                                                                                                                                        
Where,                                                                            
PAR (I)    = Total PAR incoming above the canopy, Wm^-2.
PAR (T)   = PAR transmitted to ground, Wm^-2.
PAR (R) = PAR reflected from the canopy, Wm^-2.
 
Seed yield
 
After sun drying for a few days, the harvested crop from respective net plot was threshed with thresher. Seed yield was recorded and expressed as q ha^-1.

Emergence count
 
Emergence count forms the basis for optimum plant population necessary for securing better yield of crop. During 2015 (Table 1), significantly higher emergence count was recorded in bed planting methods from 4^th day after sowing to 8^th days after sowing. At 8^th DAS, bed planted crop recorded 8.3% higher emergence count than flat planted method. Significantly increase in emergence count in bed planted was observed which might be due to the availability of adequate soil conditions in bed planted method than flat planted method. During 2016, similar results were recorded under bed planted method as compared to flat planted method. At 4^th DAS, 16.8% more emergence count was recorded with bed planted crop same as at 8^th DAS 5.9% additional emergence count was recorded with bed planted method of sowing.
 

       
Seed priming significantly affect the emergence count of the crop in both the years. During 2015, significantly higher emergence count was recorded with 100 ppm GA₃ primed seeds as compared to non-primed/dry seeds. Results showed that at 4^th DAS primed seeds recorded 12.5% higher emergence than non-primed seeds. At 8^th DAS, significant 9.94% increase in emergence count was recorded with 100 ppm GA₃ treated seeds. During 2016, Primed seeds recorded 18.4% more emergence of seeds at 4^th DAS and 5.9% more emergence count at 8^th DAS.
       
Out of three different seed rates (50, 62.5 and 75 kg ha^-1) significantly more emergence count was recorded where 75 kg ha^-1 is used which was statistically at par with 62.5 kg ha^-1 as compared to 50 kg ha^-1 seed rate in both the two years. During 2015, at 7^th and 8^th DAS significantly higher emergence of seeds was recorded with 75 kg ha^-1 (19.5 and 21.9) as compared to other and followed by 62.5 kg ha^-1 (17.9 and 19.7). With the addition of seed rate at 8^th DAS from 62.5 to 75 kg ha^-1 it increase 11% emergence count and 19% increase in seed emergence than 50 kg ha^-1. During 2016, an increase of 7.9% in seed emergence was recorded with 75 kg ha^-1 seed rate as compared to 50 kg ha^-1 seed rate at 8^th DAS. This significant increase in emergence of soybean seed might be due to more plant population in 75 kg ha^-1.
 
Plant height
 
Plant height (Table 2) is an index of growth and development representing the infrastructure build-up over a period of time is dependent on genetic constitution of a particular cultivar and may also vary due to different agronomic manipulations which may alter the soil or above ground conditions different seed rates for the better growth of crop plants. Bed planted crop reported significantly highest plant height at 30, 60, 90 DAS and at harvest as compared to flat planted crop during 2015 and 2016, respectively. This increase in plant height might be due to better soil moisture conditions and efficient utilisation of resources in bed planted method than flat planting method. Bed planted crop recorded 14.8% higher plant height at 30 DAS and 3.3% higher plant height at harvest stage during  2015 similarly during 2016, maximum plant height was recorded with bed planted method i.e. 9.6% at 30 DAS and 3.5% at harvest of the crop, respectively.
 

       
100 ppm GA₃ primed seeds recorded significantly maximum plant height as compared to non-primed seeds in both the years. From the data presented in Table 2, it is cleared that at 30 DAS, primed seeds recorded 19.9 and 20.1 cm plant height which was 9.3 and 6.3% more than non- primed seeds during 2015 and 2016. At grand growth phase of crop (60 DAS) primed seeds recorded 25 and 12% increase in plant height and at 90 DAS, 6.8 and 5.7% increase in height was recorded in both the two years. This increase in plant height is might be due to more physiological activities which in turns enhance the metabolic activities and produce more enzymes for better utilization of stored food reserves.
 
Non-significant effect was recorded with different seed rate on plant height of soybean crop during both the experimental years. Out of three seed rates, 62.5 kg ha^-1 recorded comparative better plant height as compared to 75 and 50 kg ha^-1 seed rate during 2015 and 2016. Approximate 2.6 and 4.8 % more plant height was observed at initial stage (30 DAS) of crop with 62.5 kg ha^-1 than 75 and 50 kg ha^-1 during 2015. At 60 DAS, plant height was 55.8 and 60.2 cm recorded with 62.5 kg ha^-1 during 2016. Lone et al., (2010) also recorded higher soybean plant height in higher seed rate treatments. Rahman et al., (2011) observed that plant height increased with increase in plant density up to 100 plants m^-2 then declined with further increase in plant density. Same research findings were also reported by Rahman et al., (2004)  in soybean crop.
 
Dry matter accumulation (DMA)
 
DMA is an important index reflecting the growth and metabolic efficiency of the plant which ultimately influence the yield of crop. It increased progressively with advancement in crop age and starts declining after 90 DAS. Table 2 shows that DMA was significantly affected with different planting methods. Bed planted crop recorded significantly more accumulation of dry matter at 30, 60, 90 DAS and at harvest during 2015 and 2016. At 60 DAS, bed planted crop recorded 7.9 and 15.6% increase in DM in both the two years as compared to flat planting method. At 90 DAS, 23.4 and 23.6 g dry matter accumulation was recorded with bed planted crop and 13.8 and 13.9 g DM was recorded at harvest during 2015 and 2016. Maximum accumulation of plant dry matter in bed planted crop might be due to better emergence of the crop and plant height which leads to better development of crop plants. Bed planted method provide better moisture conditions which in turns enlarge the plant cells and reduce the early maturation of cells which leads to increase in the photosynthetic area and hence increases the DMA in bed planted crop. Ram and Kler (2007) also reported that bed planting of soybean improved light penetration in middle and bottom of crop canopy resulting in dry matter accumulation.
       
With respect to primed and non-primed seeds, significantly higher DMA was recorded with GA₃ primed seeds as compared to non-primed seeds. During both the years at 30 DAS primed seeds recorded 5.74 and 6.64 g plant^-1 dry matter as compared to non-primed seeds which recorded 5.19 and 5.93 g plant-1 DM. At 60 DAS, primed seeds recorded 11.9 and 5.3% more DMA than non-primed seeds. At 90 DAS and at harvest primed seeds recorded approximate 6.4 and 5.4% and 8.8 and 8.7% increase in DA than non-primed seeds in both the years.
       
Different seed rate recorded significant effect on DMA of soybean crop in both the years. Seed rate of 62.5 kg ha^-1 recorded significantly higher accumulation of plant dry matter at every stage of crop which showed statistically at par result with 75 kg ha^-1 as compared to 50 kg ha^-1 in the year of 2015 and 2016. At 60 DAS, 19.1 and 19.9 g DM was recorded with 62.5 kg ha^-1 which was at par with 75 kg ha^-1 (18.7 and 19.5g plant^-1). 62.5 kg ha-1 seed rate recorded comparative higher DM as compared to 75 kg ha^-1 which might be due to fact that DMA increase with increase in plant population but more plant population cause competition between the crop plants and hence it reduces the performance and growth of the plants.
 
Leaf area index (LAI)
 
LAI is a common index of plant growth which directly influences solar radiation interception, photosynthesis and ultimately the yield. LAI indicates the total leaf area per unit of ground area which is an indication of growth and development of crop. Table 3 shows the data on LAI of bed planted soybean crop. Results shows that during 2015 and 2016, bed planted crop recorded significantly maximum values of LAI at 30, 60 and 90 DAS. When the crop was at initial stage it recorded less value of LAI i.e. 1.25 and 1.42 with bed planting method and later on it increased progressively at 90 DAS. Soybean crop attain maximum growth between 60 and 90 days after sowing. At this growth phase (60 DAS) around 16 and 15% increase in LAI was recorded at 60 DAS and approximate 26 and 26% increase in LAI was observed at 90 DAS during 2015 and 2016. This increase in LAI with bed planted method might be due to improved emergence and development of crop plants which improved the leaf canopy later on.
       
100 ppm GA₃ primed seeds recorded significant higher values of LAI as compared to non-primed seeds in both the years. Primed seeds recorded 39 and 37% increase in LAI than non-primed seeds at 60 DAS in both the years. At 90 DAS, primed seeds reported 3.93 and 4.06 LAI than non-primed seeds which recorded 3.44 and 3.63 value of LAI, respectively. This increase in LAI with respect to seed priming might be due to enhancement of physiological activities which provide food reserve to the developing seed and improves the performance of the crop plants.
       
With respect to different seed rates, during 2015 and 2016, seed rate of 62.5 kg ha^-1 recorded significantly higher values of LAI which shows statistically at par result with 70 kg ha^-1 but significantly better than 50 kg ha^-1. During 2015 and 2016, seed rate of 62.5 kg ha^-1 recorded 1.18 and 1.38 LAI value at 30 DAS which was 29.6 and 30.1% higher as compared to 50 kg ha^-1. Similarly at 60 DAS, same trend was observed during 2015 but later on in 2016 different seed rates fails to record significant result. Seed rate of 62.5 kg ha^-1 recorded better LAI than other 75 and 50 kg ha^-1. At 90 DAS only 62.5 kg ha^-1 seed rate recorded significantly higher LAI as compared to other seed rates. When 62.5 kg ha^-1 seed rate was used it recorded 10.2 and 10.6% increase in LAI than 75 kg ha^-1 seed rate at 90 DAS in both the years. Rahman et al., (2011) also reported that LAI increase with increase in seed rate in soybean crop after that it recorded statistically similar results.
 
Photosynthetic active radiation interception (PARI %)
 
The data on photosynthetically active radiation (PAR) are presented in Table 3. Results shows that at early stage of crop (at 30 DAS) non-significant affect with different planting methods was recorded in both the years but with the advancement of stages from 60 to 90 DAS, bed planted crop recorded maximum PAR which was significantly higher than flat planting method. During 2015 and 2016, bed planting method reported 84.7 and 86.1% values of PAR at 60 DAS and at 90 DAS it increase up to 86.7 and 90.8%. This increase in PAR% might be due to the fact that bed planting method provides good soil moisture conditions which in turns provide better crop growth and development. Ram et al., (2011) reported that highest PAR interception was recorded in raised bed planting which was 5.5% higher and significantly higher than raised broad bed planting but was on par with flat and ridge-furrow planting systems.
 

       
When GA₃ seeds primed at 100 ppm it recorded significantly higher values of PAR % over non-primed seeds in both the years. During 2015, primed seeds recorded 64.3, 84.9 and 87% PAR. During 2016, GA₃ used to primed soybean seeds at 100 ppm rate recorded 9.9, 3.2 and 4.4% more absorption of photosynthetic radiations than non-primed seeds. This increase in PAR% with priming of seeds might be due to the early and better development of crop plants.
       
With respect to three different seed rate, 62.5 kg ha^-1 seed rate recorded significantly more PAR% in 2015 and 2016, respectively which was statistically at par with 75 kg ha^-1. At 30 DAS, seed rate of 62.5 kg ha^-1 recorded 63.9 and 68.7% PAR which was statistically similar with 75 kg ha^-1 (61.1 and 65.5%) but significantly better than 50 kg ha^-1 which recorded 58.7 and 60.0% PAR. Similar trend was observed at 60 and 90 DAS where significant effect of 62.5 kg ha^-1 seed rate was recorded over 50 kg ha^-1 and 75 kg ha^-1 recorded statistical similar results with 62.5 kg ha^-1. Seed rate 62.5 kg ha^-1 recorded better performance of crop plant due to more canopy development and less crowding of crop plants. Similar result was reported by Ram et al., (2011). observed that highest PAR interception was observed in seed rate of 75 kg ha^-1, which was statistically on par with 62.5 kg ha^-1 but significantly higher than 50 kg ha^-1 seed rate.
 
Seed yield
 
Bed planted soybean recorded significantly higher yield i.e. 23.34 q ha^-1 and 20.92 q ha^-1 which is 25.8 and 5.92% higher as compared to flat planted method in both the years (Table 4). This increase in seed yield under bed planted crop might be due to improvement in soil physical structure, chemical and microbial status and thereby providing favourable environment for establishment, growth and development of the crop. Kaur (2003) also recorded better soybean seed yield under raised bed planting than flat planting at Ludhiana. Malik et al., (2006) and Tayyab M (2000) also reported that bed planted method recorded significantly higher seed yield as compared to flat planted system.
 

       
Significantly higher seed yield was recorded with 100 ppm GA₃ treated seeds as compared to non-primed or dry seeds during both the two years (Table 4). Primed seeds recorded 22.73 and 22.84 q ha^-1 seed yield which was increased by 18.6 and 28.0 % with the use of 100 ppm GA₃ treated seeds as compared to non-primed seeds in during 2015 and 2016. Seed priming might be attributed to improvement in growth parameters like plant height, dry matter accumulation and LAI which resulted in better utilization of solar energy which led to increased synthesis of carbohydrates, consequently resulting in increase in yield attributes and final seed yield. The superiority GA₃ to record higher field performance may be due to its stimulation effect in the formation of enzymes which are important in the early phases of germination which helps for a fast radicle protrusion and hence and hypocotyl elongation (Riedell et al., 1985 and Maske et al., 1997). Feng et al., (1997) also reported the use of GA₃ in germination of soybean seeds, suggesting that the gibberellic acid would play an important role during the germination process of seeds. Chavan et al., (2014) also reported that GA₃ treated soybean crop recorded maximum seed yield as compared to CaCl₂, KH₂PO₄ and untreated seeds.
       
Seed rate of 62.5 kg ha^-1 recorded significantly higher seed yield (22.47 and 21.06 q ha^-1) than 50 and 75 kg ha^-1 in 2015 and 2016, respectively. During 2016, seed rate of 75 kg ha^-1 recorded statistically at par result with 62.5 kg ha^-1 but significantly higher seed yield than 50 kg ha^-1. Approximate, 16 and 8.6% increase in seed yield was recorded with 62.5 kg ha^-1 seed rate than 50 kg ha^-1. In 2015 and 2016, when 75 kg ha^-1 seed was used it recorded 21.04 and 20.57 q ha^-1 final yield which was 8.9 and 6.1% higher than 50 kg ha^-1. Rahman et al., (2011) also reported seed yield per unit area increased with an increase of seed rate up to a certain level and then decreased with further increase in plant density.
       
In pooled analysis of seed yield bed planting method recorded significant higher (22.13 q ha^-1) than flat planting method. Bed planted method recorded increase of seed yield by 15.6 % as compared to flat planting method. With respect to seed priming treatments, primed seeds recorded significantly maximum seed yield (22.78 q ha^-1) as compared to non-primed seeds. An increase of 23.2 % seed yield was recorded with 100 ppm GA₃ primed seeds as compared to non primed seeds. Significantly highest seed yield was recorded when 62.5 kg ha^-1 (21.77q ha^-1) seed rate was used as compared to 50 and 75 kg ha^-1. Seed rate of 62.5 kg ha^-1 recorded increase of 4.61 % in seed yield than 75 kg ha^-1 and 12.6 % with 50 kg ha^-1 seed rate.

The results revealed that higher emergence count, plant height, DMA, LAI, PAR and final seed yield was recorded under bed planting method as compared to flat planting method. Under different priming methods, seeds primed with 100 ppm GA₃, recorded significantly higher biometric and yield as compared to non-primed or dry seeds. Primed seeds recorded 18 and 28% increase in seed yield as compared to non-primed seeds in both the two years. Seed rate of 62.5 kg ha^-1 recorded highest plant growth characters and seed yield.  It recorded 16 and 8.6 % increase in seed yield than 50 kg ha^-1 but showed statistically similar results with 75 kg ha^-1 seed rate.