Effect of Date of Sowing and Foliar Application of Nutrients on Seed Quality of Soybean

Soybean [Glycine max (L.) Merrill] crop is originated in China and distributed to Asia, USA, Brazil, Argentina etc. It is synonymously called as „Chinese pea‟ or „Manchurian bean‟ or “Golden bean” and it is emerged as a miracle crop of 20th century because it is versatile and fascinating crop. Apart from high yielding potential (30-35 q/ha), soybean is very rich in protein (40%) and edible oil (20%) contains a fairly high amount of unsaturated fatty acids and about 1.5 to 3.1 per cent lecithin which is essential for building up of nerve tissue. Soybean is the single largest oilseed produced in the world. It alone contributes about 58 per cent of the global oil seed production. It ranks first in oil seed production followed by rapeseed (13%), groundnut (8%) and sunflower (7%). Globally, soybean occupies an area of 126.6 m ha producing 346.3 mt with the productivity of International Journal of Current Microbiology and Applied Sciences ISSN: 2319-7706 Volume 7 Number 08 (2018) Journal homepage: http://www.ijcmas.com

Climatic factors like temperature, precipitation or rain, snow fall, wind, wind storms, flooding etc., have crucial role in agricultural production. In agriculture both temperature and precipitation are dominant climatic factors to affect crop yields which vary widely throughout the year and place (Alexandrov and Hoogenboom, 2001). Planting prior to or later than the optimal planting date can greatly reduce soybean yield and quality since photo periodism controls not only the number of days to flowering, but also the amount of time available for vegetative plant growth and development. Soybeans planted prior or late to optimum range often lose yield from poor emergence due to inadequate soil temperature or, when planted after the optimal range, from failure to fully develop (Bastidas et al., 2008).
To increase the productivity of soybean, it is necessary to provide adequate nutrition to the plant for growth and development. Plant nutrition plays an important role for enhancing seed yield and quality in soybean. Foliar application of nutrients was more beneficial than soil application, since application rates are lesser as compared to soil application, same results could be obtained easily and the crop reacts to nutrient application immediately (Zayed et al., 2011).
Recently, new generation fertilizers have been introduced exclusively for foliar feeding and fertilization. These fertilizers are better source for foliar application (Vibhute, 1998). These fertilizers have different ratios of N, P and K which are highly water soluble and so amenable for foliar nutrition (Jayabal et al., 1999). Quality seed production in soybean is holistic approach which involves the activities like standardization of appropriate season, time of planting and other several techniques to enhance the storability. Keeping all these aspects in view, the present investigation was undertaken.

Materials and Methods
The Field experiment was conducted during kharif season of 2016 and 2017 in MARS, University of agricultural Sciences, Dharwad. The factors of the experiment was comprised of three date of sowing (D 1 : 1 st fortnight of June, D 2 : 2 nd fortnight of June and D 3 : 1 st fortnight of July) and eight foliar spray at 45 DAS (T 1 : Water spray, T 2 : Urea spray @ 2 %, T 3 : Diammonium phosphate (DAP) @ 2 %, T 4 : Potassium phosphate (KH 2 PO 4 ) @ 1 %, T 5 : Boron @ 0.50 %, T 6 : 19:19:19 @ 3 %+ Boron @ 0.50 %, T 7 : KNO 3 @ 1 % + KH 2 PO 4 @ 0.5 % and T 8 : KNO 3 @ 0.5 % + KH 2 PO 4 @ 0.5 % + Boron 0.50 %) for DSb-21 variety of soybean. The fortnight meteorological observations during crop growth period are presented in Table 1. The seed materials from the field experiment were harvested and subjected for laboratory analysis using Completely Randomized Design with factorial concept in three replications to assess the seed quality parameters in laboratory of National Seed Project, Seed Unit and Department of Seed Science and Technology, University of Agricultural Sciences, Dharwad.

Results and Discussion
The test weight showed significant difference due to different dates of sowing (Table 2). Higher test weight was recorded in seeds sown on first fortnight of June (D 1 ) (13.74, 13.64 and 13.69 g) followed by second fortnight of June (D 2 ) recorded 13.53, 13.40 and 13.47g while, lower test weight was recorded in plots sown on first fortnight of July (D 3 ) (13.25, 13.03 and 13.14 g) during 2016, 2017 and pooled data, respectively. Seed weight significantly declined when sowing was delayed from June to July. The highest test weight recorded in first date of sowing might be due to optimum climate and sufficient time for growth and pod filling, which enabled the plants to produce bold seeds, late sowings decreased the rate of pod filling and shortened effective duration of pod filling compared with earlier sowings. Reduction in the source of assimilates at later sowing dates caused lower seed weight at harvest .
These results are in accordance with the findings of several other workers (Yari et al., 2013 andRahman et al., 2006), who reported that earlier sowings provided the short vegetative period of growth and comparatively longer reproductive and seed filling period, which significantly raised test weight.
Non-significant variations realized for standard germination per cent among different sowing dates (Table 2). Germination ranged from 93 to 97 per cent with 96 per cent as general mean. The highest germination per cent was recorded in seeds obtained from (D 1 ) first fortnight of June (96.01, 94.48 and 95.25 %) and lowest was observed in (D 3 ) July first fortnight of sowing (95.24, 94.23 and 94.74 %) during 2016, 2017 and pooled data, respectively. Higher germination (95.25 %) in case of June first fortnight of sowing might be due better environment conditions i.e., optimum temperature (23.68 °C) during seed filling, seed development, maturity and harvesting. The lowest germination (94.74 %) in seeds obtained from July first fortnight sowing might be due to the improper growth and development of plants and crop exposed to low mean temperature during maturity and harvesting stage and seeds obtained from these sowings had relatively higher moisture content and fungal infection. These findings are in conformity with Uem and Unioeste (2003) they reported that seeds obtained from the optimum sowing dates had higher per cent of germination than early or delayed planted crop because of the more favourable climatic conditions during seed development maturity.
The root length had significant difference due to different dates of sowing (Table 2). Significantly higher root length (17.40, 17.38 and 17.39 cm) was recorded in seeds sown on first fortnight of June (D 1 ) followed by second fortnight of June (D 2 ) recorded 17.18, 17.09 and 17.14 cm while, lower root length (16.82, 16.63 and 16.72 cm) was recorded in plots sown on first fortnight of July (D 3 ) during 2016, 2017 and pooled data, respectively. The results showed maximum shoot length (17.08 cm) in case of second date of sowing done at June second fortnight (D 2 ) in 2016, (17.06 cm) in June first fortnight (D 1 ) during 2017 and pooled data respectively and significantly lower shoot length (16.49, 16.31 and 16.40 cm) was observed when sowing performed on July first fortnight (D 3 ) during 2016, 2017 and pooled data, respectively ( Table 2). The significant increase in shoot and root length might be due to higher seed index as is reflected in the test weight of the seed, which might have supplied adequate food reserves to resume embryo growth. These findings are supported by Kumar et al., (2011) who reported that in niger seed quality parameters like germination percentage and seedling length were observed to be lower when the sowing date was delayed.
There was continuous decrease in dry weight of seedlings as sowing date delayed (Table 3). Sowing on first fortnight of June (D 1 ) recorded significantly higher (124.0, 121.9 and 124.0 mg) dry weight of seedlings followed by second fortnight of June (D 2 ) recorded 123.4, 120.4 and 123.0 mg and lowest (121.3, 117.2 and 120.3 mg) was recorded in (D 3 ) first fortnight of July during 2016, 2017 and pooled data, respectively.    Higher seedling dry weight (124 mg) in early sowings might be due to larger seed size which could be attributed to more food reserves in the seed ultimately resulting into good seedlings. Decrease in seedling dry weight was due to nutrients supply from mother plant was restricted to seed due to disruption of vascular connection and utilization in various physiological and metabolic processes (Khatun et al., 2009). These findings are supported by  who reported that soybean seedling dry weight decreased in seeds from late sown crop. Kasul et al., (2003) reported a significant positive correlation between weight of seed and seedling vigour and seedling dry weight.
The vigour index-I of soybean differs significantly due to different date of sowing. There was significant reduction in vigour index from June first fortnight (D 1 ) to July first fortnight (D 3 ) with maximum (3308, 3255 and 3282) observed at D 1 date of sowing and minimum (3173, 3104 and 3139) recorded at D 3 date of sowing during 2016, 2017 and pooled data, respectively (Table 3). The variation in seed germination and vigour comes from the environmental conditions that the crop experiences during the seed development and maturation (Dornbos, 1995). These findings are in line with the reports of Rahman et al., (2013) who reported that seeds from optimum time of sowing had high seedling vigour index because of high seed quality.
Seeds from June first fortnight (D 1 ) sowing recorded significantly highest Germination rate index (64.09, 64.01 and 64.05) followed by June second fortnight (D 2 ) of sowing (63.93, 63.88 and 63.91) as compared to lower Germination rate index (63.82, 63.64 and 63.73) was recorded in July first fortnight (D 3 ) of sowing during 2016, 2017 and pooled data, respectively (Table 3). Speed of germination was found to be better from seeds obtained from June first fortnight sowings. This might be due to favourable environmental conditions during seed development, high initial seed quality and higher seed size resulting into higher seed germination and seed vigour. These findings are supported by Rahman et al., (2013) who concluded that seed produced from early sowings had higher seed quality and vigour index than seed produced from delayed sowings.
Results on seed infection (%) showed that there was a significant difference among seed lots harvested from crop sown on different sowing dates ( . This might be due to seeds obtained from these sowings had relatively higher moisture content and fungal infection. These results are in contrast with findings of Khalil et al., (2001) who noticed that seeds received from early sowings had lower germination and higher infection of seed borne pathogens while, seeds from delayed sowings produced smaller seeds with higher germination and little infection with seed borne pathogens. The contrasting results might be due to differences in the weather parameters prevailed at seed maturity and harvesting.
There was significant reduction in dehydrogenase activity from June first fortnight (D 1 ) to July first fortnight (D 3 ) with maximum dehydrogenase activity (0.616, 0.612 and 0.614) observed at D 1 date of sowing and minimum (0.584, 0.569 and 0.577) recorded at D 3 date of sowing during 2016, 2017 and pooled data, respectively (Fig.  1). This might be due to high initial seed quality. These results are in conformity with Madhavi, et al., (2000). They stated that, the differences will show clearly at the maturity phase which early planting date affected the rapidly increasing the activity of dehydrogenase enzyme whereas late planting shoe slower trend.
Seeds from June first fortnight (D 1 ) sowing recorded significantly higher (18.15, 18.11 and 18.13 %) Fig. 1 and 2). This might be due foliar spray of water soluble fertilizers containing major nutrients at critical growth stages might have resulted in quick and spot availability of optimum quantity of nutrients in required form to the soybean crop. This resulted in better absorption of nutrients by leaves in soybean which might have helped in the production of more number of flowers and pods per plant, better seed setting, more number of developed seeds ultimately higher seed weight. So significantly highest seed weight were recorded in treated plots receiving 19:19:19 and KNO 3 @ 0.5 % + KH 2 PO 4 @ 0.5 % + Boron 0.5 %. The presence of potassium in 19:19:19 helps in higher supply and absorption of nitrogen by soybean leaves leading to increased chlorophyll synthesis and photosynthesis might have translocated to the developing seeds. The investigations were in accordance with the finding of Vinod Kumar et al., (2013) in soybean. Foliar application of water soluble fertilizer at pod development stage. Since, the higher nitrogen supply through foliar application at different crop growth stages resulted in enhancement of protein content of seeds, suggesting that hydrocarbons synthesized during photosynthetic process are diverted to form more of proteins (Chaurasia et al., 2005, Venkatesh andBasu, 2011). The increase in protein was also accompanied by increase in K and N in leaf tissues. Our findings were in agreement with earlier studies (Bellaloui, et al., 2010, Soybean) where they reported an increase in protein with higher K levels. Potassium is directly or indirectly involved in plant protein metabolism with K crucial in most steps of protein synthesis (Blevins, 2010, other crops). Previous research reported enhanced transport of essential amino acids at higher K fertilizer levels, especially to the developing seeds (Mengel et al., 1991 other crops).
Thus from the experiment it could be concluded that with delayed sowing, seed quality attributes were adversely affected. Small fluctuations in the weather (temperature) showed higher variations in plant growth and development, which finally influenced on the yield and quality of soybean. Considering the changes in plant growth, seed yield and quality, first fortnight of June sowing sprayed with KNO 3 @ 0.5 % + KH 2 PO 4 @ 0.5 % + Boron 0.50 % and also 19: 19: 19 @ 3 %+ Boron @ 0.50 % maintained better crop growth, seed yield and quality of soybean.