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Providing evidence to improve practice

Individual study: Winter Cover Crop Seeding Rate and Variety Effects during Eight Years of Organic Vegetables: III. Cover Crop Residue Quality and Nitrogen Mineralization

Published source details

Brennan E.B., Boyd N.S. & Smith R.F. (2013) Winter Cover Crop Seeding Rate and Variety Effects during Eight Years of Organic Vegetables: III. Cover Crop Residue Quality and Nitrogen Mineralization. Agronomy Journal, 105, 171-182


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Soil: Grow cover crops in arable fields Mediterranean Farmland

A replicated, randomized, controlled study in 2003–2005 on an irrigated vegetable farm in the Salinas Valley, California, USA, found more nitrogen in plots with winter cover crops, compared to bare fallows. Nutrients: More nitrogen (ammonium and nitrate) was found in plots with cover crops, compared to bare fallows, in some comparisons, for some cover crops (data not clearly reported; in 2005, plots that were cover cropped with legumes and rye consistently had more nitrogen than bare fallows: 5–15 vs 4–5 µg mineral N/g dry soil; in 2004, all cover cropped plots had more nitrogen in one of five comparisons: 10–17 vs 5). Implementation options: In 2005, less nitrogen was found in plots that were cover cropped with oats (3–7 µg mineral N/g dry soil), compared to legumes and rye (5–13 µg) or mustard (6–13 µg, in five of seven comparisons). In 2004, there were inconsistent differences between cover crops. Methods: Twenty-four 12 x 20 m plots were planted with winter cover crops in October 2003–2004. Each plot had one of three cover crops: Secale cereale Merced rye, mustard (Sinapis alba and Brassica juncea), or legumes and rye (Merced rye, Vicia faba, Pisum sativum, Vicia sativa, and Vicia benghalensis). The number and size of the control plots (fallows) was not clearly reported. After the cover crops were incorporated into the soil (March), soil cores were collected every 7–10 days, for six weeks (30 cm depth, 1.9 cm width, 20 bulked samples/plot).