Performance of Pod Orientation at Sowing on Germination and its Related Attributes in Peanut (Arachis hypogaea L.)

Peanut (Arachis hypogea L.), popularly known as poormen’s cashewnut, is sixth important oilseed crop; rich in oil (48-50%) and protein (26-28%) besides source of dietary fibre, minerals and vitamins (Pasupuleti et al., 2013). Asia accounts for 50% area and 60% production of groundnut of which, India holds 20% share with 4.6 million metric tonnes, produced from 4.8 million ha with productivity of 995 kg/ha (USDA, 2020). In TamilNadu, peanut occupies 3.38 lakh ha with production of 7.83 metric tonnes (Prabu, 2018). In India, it is mostly (nearly 70%) cultivated as rainfed/drylands and remaining (30%) is under irrigated conditions. Generally a seed rate of 120-125 kg/ha is adopted for both drylands and irrigated conditions and seed cost accounts for 31.40% of total variable cost (Ani et al., 2013). Hence, seed is most vital and costly input for groundnut (Bhingarde et al., 2015). The reason for enhanced seed cost is attributed to shelling and also damages caused during shelling which affects germination, plant population and initial growth (Louwaars, 1992).  That’s why, in Southern and Northern China, practice of pod sowing in groundnut has been a pimped technology for increasing productivity and reducing input cost (Yu, 2004; Chen et al., 2009: Chang and Zheng, 2013). Pod sowing also helps in combating frequent drought, delayed monsoon through protection given by shell to keep kernels intact from unfavourable conditions (Fu, 2009; Na, 2010). Though pod sowing enlists various positives viz., reduction in seed cost, lower seeding time, protection of kernels from birds and insects, better viability, still germination in pod-sown groundnut is considered as foremost problem due to many factors such as early sprout development issues (Ma and Hasenstein, 2006) and right position of seed in pod (Bowers and Hayden,1972). Though seed germination depends upon type and local environment conditions, seed orientation at sowing can also have an impact on germination rate, seedling physiology and morphology (Kevin et al., 2015; Tahere et al., 2005). Swaminathan et al., (1993) found that disposition of seed is not only factor to determine germination of species but also orientation of micropyle is important. Effects of sowing orientations of groundnut in kernel sowing were reported by (Ahn et al., 2017). Therefore, we need to investigate effect of sowing orientation of pods on germination and yield and hence this study.

Field experiment was conducted at Agricultural College and Research Institute, Tamil Nadu Agricultural University, Madurai, India during summer, 2020; geographically located at 9°54 N latitude, 78°5¢ E longitude and at an altitude of 147 m above sea level. The soil was sandy clay loam. Double seeded pods of 400 were chosen for each treatment and each treatment was replicated by tetrad (ISTA, 1985). Pods were shelled to collect kernels. Selected pods and kernels were sown in flat beds with spacing of 30 x10 cm by four different sowing orientations (Fig 1) viz., (i) vertical posterior-upwards (ii) vertical posterior downwards (iii) horizontal sowing and (iv) sowing with kernels (farmers practice). The variety used was VRI 8. Pod sowing was done on February 19, 2020. Fertilizers were applied as per recommended dose at 25:50:75 of NPK kg/ha in splits as basal, 20 and 45 DAS respectively and 80 kg S as gypsum at 45 days after sowing (DAS).


       
Germination was considered once shoot is emerged above soil (Bahuguna et al., 1987) and thereafter number of germinants was counted daily from onset of germination up to 21 days (ISTA, 1985). Data on daily count of germinants were used to calculate various germination indices. Plot yield was also recorded to get a broader understanding. From daily counts, following parameters were computed. a) Germination percentage (Li et al., 2010), b) Germination energy (Maguire, 1962),c) Germination value (Czabator, 1962), d) Germination Value (Djavanshir and Pourbeik, 1976), e) Germination relative index (Sreevatsava and Sareen, 1972), f) Emergence energy value (Bahuguna et al., 1987).
       
Germination percentage was computed by number of germinated seeds was counted daily by visual counting up to 10 days. Where;
n = Sum of number of seeds germinated.
N = Total number of seeds placed for germination.

Germination energy (GE) was calculated by formula Where:
Xn = Number of germinants on nth counting date.
Yn = Number of days from sowing to nth count.
       
Germination value is integral of final mean daily germination percentage (MDG) and peak value (PV).  Final MDG is cumulative percentage of full seed germination at end of test divided by number of days elapsed since sowing date. Peak value is maximum mean daily germination obtained by dividing maximum cumulative percentage reached at any time during test period by number of days from sowing when that maximum was reached. Germination value (GV) was given by formula, Where:
GV = Germination value.
GP = Germination percentage at end of test.
DGS = Daily germination speed obtained by dividing cumulative germination percentage by number of days since sowing.
DGS = Summation of all DGS figures.
N = Number of daily counts effective from date of first germination.

Emergence energy value (EEV) is highest value obtained when germination percentage on a day is divided by number of days since test when that germination percentage was reached.

Germination relative index (GRI) was computed by Where:
Xn = Number of germinants at n^th count.
h = Total number of counts.
n = Count number.

All data on observations were recorded and subjected to (ANOVA) Panse and Sukhatme, (1967).

The results of study are presented in Table 1 and Table 2. Uniformity in germination was a major problem when groundnut was sown as pods (Kerle, 1918). But according to Sun et al., (2007) and Lu et al., (2011) pod sowing of groundnut ensures germination as shell protects kernel.  Germination process is constituted by three partial processes, including imbibition, activation process and intra seminal growth that is completed with embryo protrusion (Labouriau, 1983) Groundnut seed requires 35% seed moisture for germination and 50% water content for radical emergence (Mixon , 1971).




 
Pod sowing orientations on germination and related parameters.
 
A perusal of data presented in Table 1 indicates that germination and related attributes were significantly influenced with different pod sowing orientations. Seed germination was rapid when seeds were sown as kernels over pod-sown groundnut as germination started on 4 DAS in kernel sowing and 8 DAS in pod-sown groundnut. Germination percentage was also highest in kernel sowing (98.11 %) as kernels might have easily taken up water and facilitated imbibitions of seed coat with less requirement of energy to germinate and there is no barrier provided by shell and stimulates easy germination. In pod-sown groundnut, sowing with vertical posterior - downwards recorded superior germination percentage of (97.45%). The result was correlated with Swaminathan et al., (1993) when sowing of Derris indica vertically with micropyle directed downwards. There is no difference between two other orientations (horizontal and vertical posterior - upwards). Foremost and initial activity of germination is imbibitions but shell acts as a barrier in pod-sown groundnut as it takes more time for imbibition. However, germination was, though, delayed in pod-sown groundnut, it was not affected.
 
Germination energy and germination value
 
Germination rate is a daily countable method used to evaluate seedlings vigour in laboratory and field conditions (Maguire 1962). Ranal and Santane, (2006) found that germination rate is useful for comparisons when samples/treatments present the same germinabilities. Germination value combines total germination capacity and germination energy and hence it is a better measure of seed performance and also an integrated measure of seed quality (Coastales and Veracion, 1978; Swaminathan et al., 1991, 1993). Among different sowing orientations, kernel sowing was distinctly superior in germination energy (17.67), from stand-point of all other germination related attributes. In pod sowing, pod-sown groundnut with vertical posterior-downwards recorded highest germination energy (11.93), germination value of 28.26 (Czabator 1962) and 4.59 (Djavanshir and Pourbeik, 1976) and emergence energy value (7.19) and this may be due to direction of hypocotyl inside shell that is end downward position. Similar results were observed by Ahn et al., (2017) when sowing of kernels in oak sawdust with different orientations. Bowers and Hayden (1972) revealed that there is always a close relationship between seed orientation and germination. Least germination energy and germination value was recorded with vertical posterior-upwards.
 
Emergence energy value and germination relative index
 
Emergence energy value (EEV) indicates number of germinants and germination relative index (GRI) reflects percentage of germination on each day of germination period. A EEV of 7.44 and GRI of 1553 was observed in kernel sowing while vertical posterior-downwards recorded superior EEV (7.19) and GRI (1216). Higher GRI values indicate higher and faster germination (Kader, 2005). Better EEV was registered in treatments which uptake more water and better activation and synthesis of enzymes, proteins and soluble sugars during initiation of germination. These results were in accordance with Jyotsna and Srivastava (1998). Lowest EEV and GRI were recorded in pod-sown with vertical posterior-upwards, as supported by Masilamani et al., (1999). When kernels placed with hypocotyl upwards adversely affects seedling growth and shape. However, slow emergence results in weaker seedlings or poor sowing method (Yu, 2004) and improper orientation of seed/pod are more prone to poor growth and diseases.
 
Yield and yield attributes.
 
A close observation on yield and yield attributes (Table 2) of different sowing orientation of groundnut indicated superiority of vertical posterior-downwards orientation with values of single plant pod weight (63.25 gm) and higher pod yield/m 2 (1.89kg). It was at par with kernel sowing. These results are in similarity with Kuldeep Singh and Sharma (2018) under North- South row orientations in wheat. Lowest pod and single plant pod weight was observed in horizontal sowing. Uniformity and percentage seedling emergence of direct seeded crops have major impact on final yield and quality of crop. Significantly higher kernel (0.61kg yield/m²) and DMP (7.65kg/ha) was recorded in Vertical posterior-downwards sowing and it was followed by kernel sowing (0.57kg/m² and 5.04 kg/m²). These results were in accordance with Prabu (2018) in water soaked single pods.  Higher yields and, higher field emergence and pod yield were reported by Narayanaswamy and Channarayappa (1996) in groundnut.

This study clearly indicated that orientation of pods at sowing had a little effect on germination, growth and yield of pod-sown groundnut as compared to kernel sowing. This study proved that though germination was delayed in pod-sown groundnut, it did not affect germination process, growth parameters and yield. Pod-sown groundnut may help farmers in timely sowing to overcome delayed monsoon sowing, seed shortage and labour problem especially in dry/rainfed regions.

Support from Department of Family Resource Management, Community Science College and Research Institute, TNAU, Madurai, India in field experimentation is appreciated.