Neither wood ash application nor phosphorus-fertilisation mitigated the negative effects of whole-tree harvesting on a temperate oligotrophic forest.

Background and Aims: Concerns about climate change and carbon economy have prompted the promotion of alternative energy sources, including forest-based bioenergy. An evaluation of the environmental consequences of intensive harvests (stumps and roots, and also branches and foliage) for energy wood supply, and use of wood-ash recycling as a compensatory practice, helps in the analysis of the use of forest biomass for energy production. Methods: After 11 years, we made use of records from a split-plot experimental site crossing four different intensities of Biomass Harvesting (Stem-Only Harvest [SOH], Aboveground Additional Harvest [AAH], Belowground Additional Harvest [BAH], and Whole-Tree Harvest [WTH]) and three Compensation Methods (control [C], wood ash application [A] and phosphorus fertilisation [P]) to evaluate their effects on tree growth, soil fertility, chemical properties and soil carbon. This site is located in a maritime pine forest on a poor soil, under a warm temperate climate (SW France). Key results: Despite their low additional biomass exports (+10% for AAH to +34% for WTH), the non-conventional harvest practices exported much higher quantities of nutrients than the conventional SOH technique (for example +145% for N and K in WTH). Consequently, these treatments had several effects on the soil nutritive status. Additional biomass harvests impacted the soil organic matter content, with negative effects on P-organic and soil cation exchange capacity. However, data suggested that tree growth and foliage nutrient content had not yet been significantly impacted by harvest treatments, whereas tree nutritional status was improved by P-fertiliser or wood ash. As expected, we observed a positive effect of wood ash application on soil acidity and nutrient content but, like additional harvests, wood ash application decreased the pool of soil organic carbon (~10% of the initial stock with ~7% of N-total losses). Conclusions: Overall, this factorial experiment showed that exporting more forest biomass due to the additional harvesting of tree canopies, stumps and roots had negative consequences on the ecosystem. Additional harvests have aggravated the poverty of the already oligotrophic soil, which in turn may decrease tree growth and the soil organic carbon content in the future (but without any impact on either soil acidity or on trace metal contents). Importantly, applying nutrients as fertiliser or wood ash did not compensate for the negative impact of biomass exports and the method of wood ash recycling in forests could even decrease the soil organic carbon.

AGRONOMIC PERFORMANCE OF ROCKET AS A FUNCTION OF PHOSPHORUS FERTILISATION IN A P-RICH SOIL1

ABSTRACT In intensive vegetable production systems, it is natural to increase nutrient contents in the soil due to the frequent fertiliser applications, especially phosphorus (P). There are few studies on the response of vegetables to phosphate fertilisation under such conditions. In this context, the objective of this study was to evaluate the agronomic performance of rocket as a function of phosphorus fertilisation in a P-rich Rhodic Eutrudox soil. Five P doses (0, 50, 100, 200, and 300 kg ha-1 P2O5) were evaluated in a randomised complete block design with four replicates. Maximum soil P content and shoot P content at harvest were obtained at a dose of 300 kg ha-1 P2O5. Rocket responded negatively to P fertilisation. The increase of P doses promoted the decrease of height and yield of the crop.

Carbon stability in a texture contrast soil in response to depth and long-term phosphorus fertilisation of grazed pasture

It is important to understand the stability of soil organic matter (SOM) sequestered through land management changes. In this study we assessed differences in carbon (C) stability of pasture soils that had high and low C content (2.35% vs 1.73% whole soil C in the 0–10 cm layer) resulting from long-term phosphorus fertilisation. We used soil size fractionation (fine fraction, coarse fraction and winnowing) to assess the amount of stable C and indicators of microbial decomposition capacity (catabolic profiles, metabolic quotient) to assess C stability. As a main effect throughout the 60-cm profile, C concentrations were higher in the fine fraction soil in the high (excess P fertiliser; P2) than low (no P fertiliser; P0) treatments, demonstrating a larger stable C fraction. For both P2 and P0, there was a strong correlation between C measured in the fine fraction and winnowed fraction in the 0–30 cm layer (R = 0.985, P < 0.001), but no correlation was observed for the 30–60 cm layer (R = 0.121, P > 0.05). In addition, we conducted two incubation experiments to assess C stability in the treatments with depth and to assess C stability in the physical soil fractions. For the surface soils (0–10 cm), the highest respiration occurred in fractions containing plant material, including roots (coarse fraction, 0.65 g CO2-C kg–1 soil; whole soil, 1.48 g CO2-C kg–1 soil), which shows that the plant material was less stable than the fine and winnowed soil fractions (0.43 and 0.40 g CO2-C kg–1 soil respectively). Soil respiration, microbial metabolic quotient and substrate utilisation were similar in P0 and P2. Collectively, the data show that the increased C in P2 was associated with increased C concentrations in the more stable fine soil fraction, but with no change in the stability of the C within the fractions.

Optimisation of phosphorus fertilisation promotes biomass and phosphorus nutrient accumulation, partitioning and translocation in three cotton (Gossypium hirsutum) genotypes

Limited information is available on accumulation, distribution, and remobilisation of dry matter (DM) and nutrients in cotton (Gossypium hirsutum L.) under the interaction of nutrient management and genotype. We conducted a 2-year field experiment to study the impacts of phosphorus (P) treatments (0, 16.5, 33, 66, 132 and 198 kg P ha–1) on growth and P absorption, allocation and remobilisation in three cotton genotypes. At maturity, the maximum DM and P content allocation to seeds were 20.7% and 62.3%, respectively. Compared with the anthesis stage, leaf DM and P content at maturity significantly decreased by 46.3% and 73.6%, respectively; thus, seed P content was mainly contributed by leaves. Compared with the control (nil P), optimal P fertilisation (33–66 kg P ha–1) increased leaf DM and P content at anthesis by 21.2% and 40.8%, promoted P translocation from leaves to seeds by 43%, and improved lint yield at maturity by 22.8%. At anthesis and maturity, the DM and P content of the entire plant, and lint and seed yields were higher in genotypes XLZ57 and XLZ19 than in XLZ13. Suitable P doses increase DM and P accumulation and yield, and improve source–sink relationships of DM and P in cotton.