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D-CODER is a fertilizer with a new slow-release mechanism consisting of an organo-mineral matrix that releases the nutrients only in the presence of growing plants. Pot and field experiments were carried out to study the release pattern of N from D-CODER. The experiments included grown and bare soil plots. The fertilizer treatments were D-CODER, ammonium nitrate (ANpreplant), and the control. A fourth treatment was added to the cultivated plots, consisting of splitting the ammonium nitrate application of 25% at preplant and 75% as top-dressing (ANsplit). In the bare soil pots, 35 days after the fertilizer application (DAFA), NO₃-N concentrations in the extracts of anion exchange membranes incubated in the soil for ANpreplant, D-CODER, and the control treatments were 118.5, 82.5 and 34.5 mg L^-1, respectively, suggesting that part of N from D-CODER had not yet been released. In the pots cultivated with ryegrass, 209 DAFA, N recoveries for D-CODER, ANpreplant, and control treatments were 0.94, 0.86 and 0.20 g pot^-1, respectively, suggesting that in the presence of the growing plants the release of N from D-CODER had not been restricted. Furthermore, soil NO₃-N levels in the bare soil plots of the field experiment were significantly higher in D-CODER (38.1 and 6.8 mg kg^-1 on November and March) in comparison to ANpreplant (26.3 and 5.1 mg kg^-1 on Nov. and March) treatments, suggesting that N from D-CODER was better protected from leaching. In the absence of growing plants, D-CODER provided some protection of N at least until 65 DAFA. In cultivated soils, it seemed less effective, particularly if the risk of nitrate leaching persisted for a long period of time. In these situations, a split application of N was a better strategy.

Keywords: Anion exchange membranes, Nutrient bioavailability, Rhizosphere-controlled fertilizers, Slow-‎release fertilizers.‎

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