This trial will be a complete factorial with 3 irrigation levels, 3 fertilizer levels and 4 replications (2 on each site). In each treatment there will be an equal number of trees with cones (+) and where all cones are removed (0). Removal of cones will be considered to understand what resources are being allocated by the tree to cones. Such removal shall expect to increase the growth of other biomass compartments (e.g. branches). In addition, there will be a replicate for destructive sampling on each site.
The 3 irrigation levels will be zero, one concentrated in June and July and another which will receive water throughout the summer drought period. The intermediate irrigation level will be based on recent work showing water stress as an important limiting factor for nut yield and showing also that a weekly 50 liter per tree irrigation during June and July, considered as the period of main cone growth, had a strong positive influence on nut yield (Mutke et al. 2007a; Mutke et al. 2007b).
The 3 fertilization levels will be zero, corrective fertilization and corrective fertilization plus additional levels of fertilization on the second and third year. The corrective fertilization will use a balanced fertilizer suggested by to a previous soil analysis. The highest level of fertilization will include not only the corrective fertilization but will also have an annual N fertilization. N fertilization is thought to have a positive impact on nut yield (Calama et al. 2007b). Foliar analysis for each plot will be done every year to assess foliar nutrient contents in response to the treatments: nitrogen (N), phosphorus (P), potassium, (K), calcium (Ca), magnesium (Mg), sulphur (S), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu) and boron (B) concentrations will be determined. This will give information on the nutrient status of trees and help identify deficiencies and/or toxicity symptoms.
A field survey across the Portuguese distribution of stone pines has been already carried out with several of the project team researchers, as well as forest owners, in order to locate suitable stands for establishing the trials. Two sites will be selected, one with a high, and the other with an average growth rate. Selecting two sites rather than one will provide a wider range and applicability for the results from this trial. The stands will have already started to produce cones. They will have established root systems so irrigation should not affect the stability of the trees. The stands will also still be young enough to respond well to changes in water and nutrient regimes.
A weather station will be established on each site to record climatic data, including solar radiation, atmospheric vapor pressure deficit (VPD), rainfall, frost days per month and average temperature. Soil water will be monitored, for every treatment in one block per site. Photosynthetic light response will be measured and when measured in the irrigated and fertilized treatment maximum quantum efficiency will be calculated from the slope of the photosynthetic light response as PAR approach zero.
Tree height, diameter at breast height (1.3 m) and branch diameter of selected branches with and without cones will be measured monthly during the growing season. Cones will be collected every year and the weight will be recorded. Destructive sampling will quantify above ground and belowground Pinus pinea biomass.