The Field Performance of Some Soybean Cultivars [Glycine max (L.) Merrill] Cultivated As a Main and a Second Crop

Soybean [Glycine max (L.) Merr.], with high oil and protein content, is one of the world's main nutritional sources and millions of hectares are given over to its cultivation. Intensive farming, producing multiple crops per year (such as second-crop soybean cultivation), can improve natural resource exploitation and productivity. An optimal sowing date avoids significant yield losses. This research was carried out in the plain conditions of Mardin province in Turkey in 2018 and 2019. Since the region is suitable for growing double crops per year, soybean field trials were carried out both as a main crop and as a second-cropped. The A-3127, Arısoy, Ataem-7, Blaze, Bravo, Cinsoy, Gapsoy-16, Lider, May-5312, Nova, SA-88, and Umut-2002 cultivars were used as plant material in this research. The first sowing took place on April 16, the second on April 25, the third on June 15, and the fourth on June 30 in both years of the research. Two sowings were main crop, while the other two were second-crop. A-3127 and Gapsoy-16 cultivars produced the highest seed yields (3700.1 and 3693.8 kg ha-1, respectively). The Gapsoy-16, Arısoy, A-3127, and Cinsoy cultivars yielded the most oil yield (675.7, 675.6, 661.8, and 661.8 kg ha-1, respectively). The study determined that early sowing increases overall yield and late sowing decreases seed yield significantly (on average by 30%). However, both in this region and in areas with similar agricultural environments where double-crop can be grown each year, early varieties for a second-crop may be recommended to reduce the vegetable food and oil deficit.