Long-Term Effect of Organic and Mineral Fertilization on Soil Physical Properties Under Greenhouse and Outdoor Management Practices

To evaluate the use of organic amendments as an alternative to conventional fertilization, a 10-year experiment on a loam soil was conducted under a crop rotation system in both greenhouse and outdoor plots applied with chemical fertilizers (NPK) and vegetal compost (organic fertilizer) in the Guadalquivir River Valley, Spain. The effect of these two different fertilization regimes on the soil physical properties was evaluated. Soil organic carbon (OC), soil bulk density (BD), soil water retention (WR), available water content (AWC), aggregate stability (AS), and soil physical quality (Dexter's index, S) were determined. The use of organic fertilizer increased OC and resulted in a significant increase in AS and a decrease in BD compared to the mineral fertilizer application in both greenhouse and outdoor plots. The outdoor plots showed the lowest BD values whereas the greenhouse plots showed the highest AS values. In the last years of the 10-year experiment the S parameter was significantly higher in organic fertilizer plots, especially for greenhouse plots. At the end of the study period, there were no significant differences in WR at field capacity (FC) between treatments in both systems; the AWC was also similar in the greenhouse plots but higher in the mineral outdoor plots. In mineral fertilizer treatments, a small improvement in the physical properties was also observed due to the utilization of less aggressive tillage compared with the previous intensive cropping system. Physical soil properties were correlated with soil OC. The sustainable management techniques such as the use of organic amendments and low or no tillage improved soil physical properties, despite the differences in management that logically significantly affected the results.