Short-term effects of different organic amendments on soil properties and organic broccoli growth and yield

The aim of this study was to evaluate the effects of different organic fertility sources on organic broccoli (Brassica oleracea var. italica) growth and yield, and on soil properties. The fertilization was designed to supply the crop with about 100 kg ha-1 of N using two amendments: a municipal solid wastes-based compost (CC), and a manure based compost (CB). The former was used alone (T1), in combination with its own water extract (CT) in fertigation (T2), and in combination to CT applied in fertigation and as foliar spray (T3). Other treatments resulted from the application of (i) CC and CB (T4); (ii) CB alone (T5); and (iii) the exhausted compost (EX) resulting from the extraction of CT (T6). Unamended plots were used as control (T7). Selected soil properties were determined at the beginning and at the end of the trial in order to estimate the effects of the various treatments on these parameters. The best yields were obtained with T4 and T5 (16.95 and 18.46 t ha-1, respectively). The application of CC alone (T1) showed slightly better growing parameters in comparison to its application in combination to CT (T2 and T3), even though the yields were not significantly different from each other. T6 showed the lowest yield of broccoli (7.03 t ha-1) among the treatments, superior only to the unfertilized control (5.38 t ha-1, T7). The different fertilizations showed a general soil enrichment of available phosphorous and organic matter, even if the latter could be only transitory. Finally, the high production costs and the low yields obtained apparently dissuade the use of compost tea and exhausted compost for the fertilization of broccoli crop.