Planting Season and Harvest Date Effects on Dry Matter Production and Nutritional Value of Brassicaspp. in the Southern Great Plains1

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Abstract
Brassicaspp. may serve as high‐quality forage crops in parts of the Southern Great Plains when most warm‐ and cool‐season forages are unproductive. Field studies were conducted to assess the forage (shoot and/or root) yields, crude protein (CP), and digestibility (IVDMD) of turnip root crops (Brassica rapaL., ‘Purpletop’, ‘Cyclon’, ‘Frisia ’, and ‘Tyfon’; a Chinese cabbage × stubble turnip hybrid) and leafy‐stem crops [‘Winfred’ rape (B. napusL.) and ‘Merlin’ kale (B. oleruceaL.)] at different harvest dates. All six Brassicaswere established on a Dale silt loam soil (fine‐silty, mixed, thermic, Pachic Haplustoll) in September 1982 and 1983 (fall) and March 1983 and 1984 (spring) under dryland conditions. Shoot dry matter (DM) production for root crop cultivars was highest 85 and 95 days after planting in fall and spring, respectively. The greatest total plant DM yield was produced by Cyclon in the fall and Purpletop in the spring (7.4 and 7.6 Mg ha−1, respectively). Cyclon and Tyfon produced 0.7 Mg ha−1more shoot DM, whereas Purpletop and Frisia produced 0.4 to 0.9 Mg ha−1more root DM during their maximum DM production period. In early harvests, DM yields of kale were less than those of rape, but after 90 days growth, yields were similar (7.0 Mg ha−1). Shoot CP levels of root crops averaged 220 g kg−1and were about 25 to 60 g kg−1greater than root levels. The IVDMD of mots ranged from 670 to 840 g kg−1and were approximately 60 to 120 g kg−1higher than values for shoots. Levels of DM, CP, and IVDMD for all cultivars were similar or better in fall growing season and did not decline as rapidly compared with spring. Cyclon and Purpletop have the potential to provide high yields of high‐quality forage during the forage deficit periods of Southern Great Plains.
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