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.Peer Reviewe

A short-term comparison of organic v. conventional agriculture in a silty loam soil using two organic amendments

The transition from conventional to organic farming is accompanied by changes in soil chemical properties and processes that could affect soil fertility. The organic system is very complex and the present work carries out a short-term comparison of the effects of organic and conventional agriculture on the chemical properties of a silty loam soil (Xerofluvent) located in the Guadalquivir River Valley, Seville, Spain, through a succession of five crop cycles over a 3-year period. Crop rotation and varieties were compared in a conventional system using inorganic fertilizer and two organic systems using either plant compost or manure. At the end of the study, organic farming management resulted in higher soil organic carbon (OC), N and available P, K, Fe and Zn. The available Mn and especially Cu values did not show significant differences. In general, treatment with manure resulted in more rapid increases in soil nutrient values than did plant compost, which had an effect on several crop cycles later. The present study demonstrated that the use of organic composts results in an increase in OC and the storage of nutrients, which can provide long-term fertility benefits. Nevertheless, at least 2-3 years of organic management are necessary, depending on compost characteristics, to observe significant differences. Average crop yields were 23% lower in organic crops. Nevertheless, only two crops showed statistically significant differences.The financial support of the Spanish Commission of Science and Technology (CICYT) under project no. AGL-2000-0493 and the Government of Andalusia through Projects PAI RMN 166, and exp. 92162/1 are acknowledged.Peer Reviewe

Comparison of nutritional quality of the crops grown in an organic and conventional fertilized soil

Organic farming is growing rapidly in its potential for producing healthy foods and has been adopted in a wide range of climate and soil types. The perception among consumers is that organically produced crops possess higher nutritional quality. However, there are many factors that can affect the nutritional quality of crops, and few studies have been able to account for these differences. A comparative long-term study of organic versus mineral fertilisation has been conducted for nine years in a calcareous loamy soil classified as Xerofluvent in the Guadalquivir River Valley, near Seville, Spain. The macronutrient concentration, dry matter and nitrate content in the edible part of the plants over the last five years of the experiment were examined. We found that the nitrate concentration in the edible parts was significantly lower in crops grown in organically fertilised plots. We also found a tendency for lower N and higher P content in organic crops cultivated in same crop cycle. However, the results also showed variability in the nutritional parameters for the same crop but cultivated in different years. We conclude that it is not possible to assert a higher nutritional quality of organic crops according only to the criteria of fertiliser type; other factors, such as fertiliser characteristics and management in each particular crop cycle, exert a higher influence on the nutrient content of crops.Peer Reviewe

Comparative tree growth, phenology and fruit yield of several Japanese plum cultivars in two newly established orchards, organic and conventionally managed

The growth, phenology and fruit yield of 14 Japanese plum cultivars (Prunus salicina Lindl) were studied in two newly established experimental orchards under organic and conventional management. The experiment was conducted during 2005-2011 in the province of Seville (SW Spain), an important region of Japanese plum culture. Trunk cross-section areas (TCSA), flowering, yield and tree defoliation before winter dormancy were analysed over several years. After one year, TCSA were larger in the organically managed orchard (OMO) for most of the cultivars, in the next two years they were equal, and from the fourth year, several cultivars showed significantly larger TCSA in the conventionally managed orchard (CMO). Flowering in the conventional orchard started from 2 to 6 days before and lasted for 3 to 5 days more than in the OMO. Several cultivars produced significantly more fruit in the CMO, being the average fruit yield in the organic orchard about 72% of the conventionally managed orchard. Autumn defoliation was significantly advanced in the organic orchard, especially in cultivars highly susceptible to rust (Tranzschelia pruni spinosae), a disease not adequately controlled in the organic orchard