Abstract. -We present V RcIc Johnson-Cousins magnitudes of field comparison stars for twelve BL Lacertae objects belonging to the largest sample of blazars which is monitored at the Perugia University Observatory. The sequences reported here can be used in the long-term CCD photometric monitoring of BL Lac objects aimed to understand the characteristics of their variability. Finding charts for all of these comparison sequences are also included in this paper.

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Nitrogen fertility management represents a crucial aspect for common wheat (Triticum aestivum L.) production, particularly when we deal with organic agriculture. Th is study was conducted to determine the eff ect of fi ve N fertilization strategies on yield, grain protein content, and N leaching risk. In a 3-yr fi eld experiment, a faba bean/wheat temporary intercropping (TIC) and four fertilization treatments with extra-farm N sources were compared. Extra-farm N sources were represented by blood meal (BM) and roasted leather (RL) (broadcast all-at-once at seeding or split into one-half at seeding and one-half at tillering in a side-dressing application). Unfertilized and mineral fertilized controls were included. Th e eff ect of the legume on TIC wheat N uptake was always positive while dry weight accumulation and yield were generally poorly aff ected. Regardless of the broadcasting method, BM treatments generally showed a slightly higher yield and grain protein content compared to wheat fertilized with roasted leather (this was also confi rmed by fertilizer release effi ciency). Th e risk of N leaching was maximum at the onset of drainage (i.e., during the fi rst phase of crop growth), so using organic fertilizers at preseeding stage appeared to be a very risky practice, especially if quick-N-releasing ones are used. Splitting the organic fertilizer rate avoided a large amount of mineralized N to be leached in the watershed during the critical stage of drainage onset. Th e TIC was the best option in terms of environmental preservation, and assured a constantly higher grain protein content compared to the other organic fertilization treatments.

Field experiments were carried out in Central Italy on several green manure species (pure or mixed) and on succeeding grain maize to find practical relationships for predicting the N effect (N absorbed by maize that derives from the actual gain in soil available N due to green manure). Actually, little information is available for Mediterranean environments, where green manure species and strategies may be other than those of northern-temperate and tropical regions. Relationships were found for maize shooting (Neff = −3.61DW + 29.75N%; R 2 = 0.67), flowering (Neff = −1.32DW + 27.47N%; R 2 = 0.66) and physiological maturity (Neff = −4.84DW + 50.43N%; R 2 = 0.74) (DW = incorporated biomass, N% = N concentration).

Nitrogen concentration in plants is normally determined by expensive and time consuming chemical analyses. As an alternative, chlorophyll meter readings and N-NO3 concentration determination in petiole sap were proposed, but these assays are not always satisfactory. Spectral reflectance values of tomato leaves obtained by visible-near infrared spectrophotometry are reported to be a powerful tool for the diagnosis of plant nutritional status. The aim of the study was to evaluate the possibility and the accuracy of the estimation of tomato leaf nitrogen concentration performed through a rapid, portable and non-destructive system, in comparison with chemical standard analyses, chlorophyll meter readings and N-NO3 concentration in petiole sap. Mean reflectance leaf values were compared to each reference chemical value by partial least squares chemometric multivariate methods. The correlation between predicted values from spectral reflectance analysis and the observed chemical values showed in the independent test highly significant correlation coefficient (r = 0.94). The utilization of the proposed system, increasing efficiency, allows better knowledge of nutritional status of tomato plants, with more detailed and sharp information and on wider areas. More detailed information both in space and time is an essential tool to increase and stabilize crop quality levels and to optimize the nutrient use efficiency.

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