Submitted to: Subtropical Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 11, 2013
Publication Date: December 1, 2012
Citation: Makus, D.J. 2012. Soil and broccoli head sulfur levels but not yields are improved by the application of gypsum to a light textured soil. Subtropical Plant Science. 64:37-43. Interpretive Summary: In the last 20 years or so, soil sulfur replenishment by rainfall, particularly in arid and semi-arid areas of the United States, has declined significantly due to changes in rainfall patterns and reductions in sulfur emissions from natural and industrial sources. Lighter textured soils tend to have relatively low sulfur levels to begin with. Gypsum is a relatively inexpensive amendment for delivering both sulfur and calcium nutrients and also improving soil properties. In this study, pre-plant application of gypsum from 0 to 2000 lbs per acre improved both soil properties and broccoli head sulfur contents as the amount of gypsum added to the soil increased. When plants were grown by conservation tillage methods (strip-tilled into plant residue), yields were similar to conventionally grown broccoli, but head size was reduced by 14%. Improving broccoli sulfur levels should also increase many of the sulfur-containing health compounds broccoli is known for.
Technical Abstract: Light textured soils in semi-arid areas can be deficient in sulfur (S). Thus, the objective of the present study was to evaluate the effects of cultivar type (open pollinated vs. hybrid), minimum (strip-tillage) vs. conventional (bedded) tilling practices, and gypsum rate (0, 500, 1000 and 2000 kg/ha) on soil properties and mineral nutrients, particularly S, and on broccoli yield and head (floret) mineral nutrient concentrations, particularly tissue S. Field-grown broccoli, Brassica oleracea Italica group (L.), cultivars Waltham 29 and Gypsy, were direct seeded into raised beds and into stripped tilled sudex residue at a site near Weslaco, TX (Lat. 26 deg 08 min). Gypsum (23% Ca and 16.5% S) at rates of 0, 500, 1000, and 2000 kg/ha were applied and incorporated in order to determine the effects of added soil S on soil properties and broccoli head mineral nutrients. Results indicate that the open-pollinated 'Waltham' is more nutrient dense than the hybrid 'Gypsy'; that tillage method does not affect broccoli head nutrients or yield, but does influence stand and head size. Increased gypsum rates improved head S concentrations (linearly), but did not affect plant stand or yield. Soil that was on raised beds tested higher in soil organic matter and extractable K, Mn, B, and Zn compared to strip-tilled soil. Gypsum application increased the soil cation exchange capacity and soil Ca and S, but linearly decreased soil Mn, B, and pH and organic matter (quadratically). Initial soil penetration force was greater in strip-tilled vs. bedded plantings, but these differences declined after 80 days. At the end of the study there was both a linear and quadratic reduction in penetration force to 15-cm depth resulting from increased gypsum application.