The dynamics of C mineralization in an organically managed Cambic Arenosol amended with hen manure, a stabilized compost (compost), and three different combinations of both fertilizers (varying from a 1:100 to a 1:10 ratio) were studied during an incubation experiment to estimate the potential of such combinations to preserve/restore soil C content relative to single applications. A strong increase of the CO 2 -C emissions relative to the unamended soil (control) was observed after soil application of all five organic-fertilizer treatments. A significantly higher amount of applied C was lost in hen-manure treatment (648 mg CO 2 -C [g C applied] -1 ) when compared to compost (159 mg CO 2 -C [g C applied] -1 ) or to the three combined treatments (176-195 mg CO 2 -C [g C applied] -1 ). The first-order exponential model and the double exponential model were used to fit the C-mineralization data in the treatments considered. Results showed that mixing "small" amounts of hen manure with compost did not affect the total amount of potentially mineralizable C, but significantly increased the mineralization rate constant. Clearly, combinations of both fertilizers promoted an initial faster mineralization of the organic matter, and consequently a faster release of nutrients, without affecting the total amount of C sequestered in soil.

No abstract

Abstract

The potential of an organically managed Cambic Arenosol to supply nitrogen (N) from either an applied commercial organic fertilizer (granulated hen manure), a compost produced on-farm, or four different mixtures of both fertilizers was studied in a laboratory incubation and a pot experiment with lettuce. In the incubation experiment, a significant higher apparent N mineralization occurred after hen-manure application (53.4% of the organic N applied) compared to compost (4.5%) or mixed-fertilizer application (8.7% to 16.7%). The apparent N mineralization in a mixed treatment consisting of compost and half rate of hen manure (15.4% of the organic N applied) was significantly higher than that estimated based on the N mineralization for compost and henmanure treatments (7.6%), proving that a combined application of both fertilizers enhanced organic-N mineralization when compared to separate fertilizer supply. In the pot experiment, a higher lettuce fresh-matter yield was obtained with hen manure (1.9 kg m -2 ) than with compost (1.7 kg m -2 ) or unfertilized control treatment (1.3 kg m -2 ). Combined application of compost with only a half rate of hen manure led to yields (2.0 kg m -2 ) equal to those obtained with only hen manure. A good correlation was observed between the N-mineralization incubation data and the N accumulated by lettuce plants in the pot experiment (r = 0.983). Hence, in the organic production of baby-leaf lettuce, a mixture of compost and hen manure appears to be a good fertilization alternative, since it allows a reduction by half of the typical amount of commercial fertilizer usually applied (granulated hen manure), cutting fertilization costs, and providing an amount of available N that allows maintaining lettuce yields.