Abstract
This study investigates the effect of irrigation (FI, all rows-irrigation; HI, alternate row irrigation; RF, rainfed) and planting geometry (PG) (SR, single-row; TR, twin-row) on soybean seed constituents. Results showed that most of these seed components were significantly affected by crop season due to contrasting precipitation and solar radiation patterns, particularly during July-August, coinciding with early reproductive and seed development stages. Both seed protein and oil levels responded positively to irrigation, while most of the amino acids were nonresponsive. The protein content ranged between 36.3 and 37.6% in 2018, while it was between 36.4 and 38.3% in 2019. Total seed oil content varied between 24.2 and 26.1% in 2018 and between 25.3 and 26.5% in 2019. Among amino acids, glycine, alanine, valine, and methionine levels were significantly higher in both FI and HI treatments. Among sugars, only sucrose was higher in response to the RF treatment, and irrigation did not affect both stachyose and raffinose. Oleic acid was higher in RF, while no significant differences were observed for linolenic and linoleic acids. Similarly, seasonal variation was significant for stearic acid content, but the 2019 season had relatively higher accumulation (stearic acid: between 4.1 and 4.5% in 2018 and from 4.6 to 4.9% in 2019). These results indicate that both irrigation and climate during seed development can alter some seed composition constituents and play critical roles in determining seed nutritional qualities.
Highlights
Soybean (Glycine max (L.) Merr.) is an important food legume crop worldwide, providing vegetable protein for millions of people and ingredients for hundreds of food and nonfood products. e seeds provide approximately 60% of the global supply of vegetable protein and are a good substitute for animal protein. e global area of soybeans in 2018 was 125.3 million ha with a production of 360 million tons (t) of grain at an average yield of 2.88 t ha−1. e United States accounts for about 35.45 million ha with a production of 240 million t and a productivity of 3.4 t ha−1 [1]
Weather data were collected from the nearest weather station, that is, Mid-South Agricultural Weather Service, Delta Research and Extension Center, Stoneville, Mississippi. e amount of precipitation received during the 2018 crop season (April-September) was 730.76 mm, while 895.60 mm was received in the 2019 season. e growing degree days (GDD) in °C were calculated using a base temperature (T base) of 10°C [15]. e crop was harvested after physiological maturity with a combine, and grain yields per ha were computed
Seed analyses were conducted according to Xue et al [16]. e updated calibration equation used was from Perten’s ermo Galactic Grams PLS IQ software, which was initially developed at the University of Minnesota and upgraded by the Perten Company. e calibration equations were established based on laboratory protocols according to Association of Official Analytical Chemists (AOAC) methods [17]
Summary
Soybean (Glycine max (L.) Merr.) is an important food legume crop worldwide, providing vegetable protein for millions of people and ingredients for hundreds of food and nonfood products. e seeds provide approximately 60% of the global supply of vegetable protein and are a good substitute for animal protein. e global area of soybeans in 2018 was 125.3 million ha with a production of 360 million tons (t) of grain at an average yield of 2.88 t ha−1. e United States accounts for about 35.45 million ha with a production of 240 million t and a productivity of 3.4 t ha−1 [1]. Soybean seed contains about 30–45% high-quality protein with essential amino acids and 15–22% oil with a high proportion of unsaturated fatty acids. The food and seed oil industry are leaning towards soybean with high oleic acid and low International Journal of Agronomy linolenic acid due to their contribution to soybean oil’s oxidative stability [2]. As higher levels of palmitic acid led to oxidative instability, its reduced levels (40 g Kg−1) are preferred by the industry for human consumption. Among sugars, both raffinose and stachyose are undesirable to the soybean food industry due to their indigestibility leading to flatulence and, in some cases, diarrhea. Higher sucrose is preferred as it improves taste and flavor in soy-based foods [4]
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