Yield and Nutraceutical Value of Lettuce and Basil Improved by a Microbial Inoculum in Greenhouse Experiments.

Members of Bacillus spp. have been widely used to enrich the soil/root interface to provide plant growth promoting activities. A new isolate, namely to Bacillus sp. VWC18, has been tested under greenhouse conditions in lettuce (Lactuca sativa L.) pots at different concentrations (103, 105, 107, and 109 CFU·mL-1) and application time (single inoculum at transplant and multiple inoculum every ten days) to evaluate the best application dose and frequency. Analysis of foliar yield, main nutrients, and minerals evidenced a significant response for all applications. The lowest (103 CFU·mL-1) and the highest doses (109 CFU·mL-1), applied every ten days until harvest, had the greatest efficacy; the nutrient yield (N, K, P, Na, Ca, Fe, Mg, Mn, Cu, and B) increased more than twice. A new randomized block design with three replicates was then performed in lettuce and basil (Ocinum basilicum L.), with the two best performing concentrations applied every ten days. In addition to previous analysis, root weight, chlorophyll, and carotenoids were also examined. Both experiments confirmed the previous results: inoculation of the substrate with Bacillus sp. VWC18 promoted plant growth, chlorophyll, and mineral uptake in both crop species. Root weight duplicated or triplicated compared to control plants, and chlorophyll concentration reached even higher values. Both parameters had a dose-dependent increase.

Fourteen years of compost application in a commercial nectarine orchard: effect on microelements and potential harmful elements in soil and plants.

The objective of this experiment was to valuate, after 14 years, the impact of annual compost applications on micronutrient and potentially toxic trace elements on nectarine tree uptake and soil fertility. The study was performed in the Po valley, Italy, on the variety Stark RedGold (grafted on GF677). Since orchard planting, the following treatments were applied, in a randomized complete block design, with four replicates: 1. unfertilized control; 2. mineral fertilization (N was supplied as NO3NH4 at 70-130 kg ha-1 year-1); 3. compost at 5 t DW ha-1 year-1; 4. compost at 10 t DW ha-1 year-1. The actual rate of application was 12.5 (LOW) and 25 (HIGH) t ha-1, since compost was concentrated in the tree row. Compost was made from domestic organic wastes mixed with pruning material from urban ornamental trees and garden management and stabilized for 3 months. The supply of compost HIGH induced an enrichment of soil total Cu, Zn and Cd, and a decrease of Fe and Co concentration; with values always below the European threshold limits for heavy metals in the soil. In addition, compost (at both rates) increased availability (DTPA-extractable) of Fe, Mn and Zn, Cd, Ni, and Pb in the top soil (0-0.15 m). Total micronutrient and trace element tree content was not affected by fertilization treatments; however, the recycled fraction returned to the soil at the end of the season through abscised leaves and pruned wood of Cu, Fe, Mn and Zn was increased by mineral fertilization; Fe and Zn also by compost HIGH. Our data show that the introduction of compost at both 12.5 and 25 t ha-1 year-1 in the row did not increase the risk of pollution related to potentially toxic trace elements and at the same time increased the bioavailability of Fe, Mn and Zn.

Soil-plant nitrogen pools in nectarine orchard in response to long-term compost application.

The search for sustainable source of N, the need of soil organic matter restoration, along with the call for recycling of organic wastes has led to a rise of the use of organic fertilizers. The aim of the present experiment was to evaluate: the effectiveness of compost application as a N fertilizer, the impact on N distribution in soil and plant and on tree performances, in a long-term experiment (14 years). The study was carried out in the Po valley, Italy and, since orchard planting (2001), the following treatments were applied: 1. unfertilized control; 2. mineral fertilization; 3. compost at a rate of 5 t DW ha-1 yr-1; 4. compost at a rate of 10 t DW ha-1 yr-1. Soil total N, potentially mineralizable, microbial and extractable N were higher in compost in comparison to mineral (fertilizer). The effect was found both in the row and in the inter-row and the rise of N fractions was evident in the shallowest soil layer of the row. Soil mineral, potentially mineralizable N was increased by mineral (11.1 mg kg-1) and compost 10 (12.4 mg kg-1) fertilization compared with control (6.7 mg kg-1). Vegetative growth and yield were increased in trees treated with mineral and compost 10; moreover, these plants were able to recycle (66.1 and 70.5 kg ha-1 yr-1, respectively) and remobilize (41.5 and 48.7 kg ha-1 yr-1, respectively) a higher amount of N than those of control and compost 5. In conclusion, organic fertilization strategy promoted the buildup of soil N reserve, meaning a capacity of the ecosystem to sequestrate N. The application of compost 10 showed a similar effect on plant growth and production as mineral fertilization, but introduced the advantage of the use of a cheap, renewable waste material, providing a new insight on N fertilization management.