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.

Biochar physico-chemical properties as affected by environmental exposure.

To best use biochar as a sustainable soil management and carbon (C) sequestration technique, we must understand the effect of environmental exposure on its physical and chemical properties because they likely vary with time. These properties play an important role in biochar's environmental behavior and delivery of ecosystem services. We measured biochar before amendment and four years after amendment to a commercial nectarine orchard at rates of 5, 15 and 30tha(-1). We combined two pycnometry techniques to measure skeletal (ρs) and envelope (ρe) density and to estimate the total pore volume of biochar particles. We also examined imbibition, which can provide information about soil hydraulic conductivity. Finally, we investigated the chemical properties, surface, inner layers atomic composition and C1s bonding state of biochar fragments through X-ray photoelectron spectroscopy (XPS). Ageing increased biochar skeletal density and reduced the water imbibition rate within fragments as a consequence of partial pore clogging. However, porosity and the volume of water stored in particles remained unchanged. Exposure reduced biochar pH, EC, and total C, but enhanced total N, nitrate-N, and ammonium-N. X-ray photoelectron spectroscopy analyses showed an increase of O, Si, N, Na, Al, Ca, Mn, and Fe surface (0-5nm) atomic composition (at%) and a reduction of C and K in aged particles, confirming the interactions of biochar with soil inorganic and organic phases. Oxidation of aged biochar fragments occurred mainly in the particle surface, and progressively decreased down to 75nm. Biochar surface chemistry changes included the development of carbonyl and carboxylate functional groups, again mainly on the particle surface. However, changes were noticeable down to 75nm, while no significant changes were measured in the deepest layer, up to 110nm. Results show unequivocal shifts in biochar physical and chemical properties/characteristics over short (~years) timescales.