ALBERT

Description: SUMMARYThe 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.

Description: SUMMARYThe application of organic composts to soil may affect the availability of micronutrients and their concentration in plants. The present field research study compared soil micronutrient extractability after 5 years of organic fertilization v. conventional inorganic fertilization. Iron (Fe), copper (Cu), manganese (Mn) and zinc (Zn) were extracted from soil using diethylene triamine pentaacetic acid (DTPA) and the data obtained were compared with the concentration of these micronutrients in the edible portion of the crop. The study was carried out on a loam soil classified as a Xerofluvent. The soil was fertilized with composted plant residues or with conventional inorganic fertilizer and all treatments were replicated four times in a randomized complete block design. In all cases a crop rotational system was applied. The use of organic fertilization resulted in a higher extractability for all the elements studied; however, the micronutrient content in the edible part of the crops was variable depending on the plant species and element. Crop yields depended on the type of crop rather than the type of soil fertilization. The present study showed that the use of plant compost and the elimination of synthetic fertilizers result in an increase of Fe, Cu, Mn and Zn extractability compared to soil treated with inorganic fertilization, which should provide long-term fertility benefits.

Description: SUMMARYA comparative study of the effect of organic fertilization at different times and doses on soil fertility and crop yield was performed over 3 years in a calcareous loamy soil. Nutrient availability in the soil and macronutrient concentration in leaves and in the edible part of the plants was examined in plots that were previously handled conventionally and ecologically for several years. The organic fertilizers used were manure compost at two doses in plots after 4 years of organic management treatment, and green residues of previous crops in plots with 10 years of organic management. In general, soil organic carbon (C), nitrogen (N), phosphorous (P) and magnesium (Mg) contents were found to be considerably greater in organically fertilized soils in comparison with soil receiving mineral fertilizer (conventional treatment (CT)). For C and N, the highest contents were observed in the long-term organic treatment (OR). However, few differences were found for potassium (K) and sodium (Na). The results obtained for electrical conductivity and pH indicated that, in general, there were no significant differences between treatments. The differences in the values of EC and pH occurred among cultivation cycles irrespective of the type of fertilization, but there was a contradictory trend for each of the above parameters. The results obtained for leaves and the edible part of the plant indicated that, in general, there were no significant differences between treatments, except for P with a trend for higher P content in organic crops. The nitrate values in leaves showed great variability, making it difficult to draw conclusions. The associations of fertilization and the chemical properties of soil with nutrient content in crops were checked by principal component analysis (PCA). For soil data, different clusters were observed between CT and OR treatments. However, PCA showed that the influence of crop type on plant nutrient concentrations was greater than type of fertilization. The effect of fertilization on crop yield was variable depending on plant species. The results indicated that organic fertilization did not cause deficiencies in the nutrient content and yield of vegetables when compared with conventional fertilization, showing that ecological management can be used effectively.