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Yield Responses and Nutrient Utilization with the Use of Chopped Grass and Clover Material as Surface Mulches in an Organic Vegetable Growing System

ABSTRACT Trials were performed with red beet and white cabbage in 1998–2001 to assess the effects on yields and nutrient utilization of surface mulch (chopped grass and/or red clover). No other nutrients were applied. Nitrogen (N), phosphorus (P) and potassium (K) contents were measured in mulch, saleable products and above-ground plant residues. A single mulch application of about 12 Mg DM ha−1 increased the yields of both crops significantly. Mean yields of saleable products were increased from 27 to 33, and from 44 to 56 Mg FW ha−1 of red beet and white cabbage, respectively. However, the average apparent recoveries of mulch derived nutrients in above-ground plant parts, calculated by subtraction of uptakes in the control treatment, were only 13, 14 and 18% of N, P and K, respectively. Some 3–10% of the N supplied in mulch was found as mineral N at 0–60 cm soil depth after harvest, and in late autumn approximately half of the P and all the K supplied was found as P-AL or K-AL (ammonium lactate and acetic acid) plus acid-soluble K in the topsoil. Mulch application also increased the yield level of spring cereals grown in the following year by on average 0.6 Mg ha−1, or 20%.