During the 1999 and 2000 growing seasons in Illinois, studies were conducted to determine the influence of two pollinizers (`Crimson Sweet' and `Fiesta') and three pollinizer frequencies (11%, 20%, and 33%) on `Millionaire' seedless watermelon (Citrullus lanatus) quality and yields. More large-sized [>16 lb (7.2 kg)] `Millionaire' watermelons were produced when `Crimson Sweet' was used as the pollinizer compared to `Fiesta', which resulted in `Crimson Sweet' leading to greater marketable and total `Millionaire' yields. Pollinizers responded similarly over the pollinizer frequencies for `Millionaire' watermelon yields as no pollinizer by pollinizer frequency interaction was observed. The 20% and 33% pollinizer frequencies produced similar `Millionaire' yields per acre and both resulted in greater yields compared to the 11% pollinizer frequency. Soluble solids in `Millionaire' fruits were not influenced by pollinizer or pollinizer frequency. However, hollow heart disorder followed a quadratic response with respect to pollinizer frequency with the lowest amount of hollow heart observed at the 33% pollinizer frequency and greatest at the 11% pollinizer frequency. No significant interaction (P ≤ 0.05) was observed for pollinizer by pollinizer frequency for hollow heart disorder in `Millionaire'; although, more hollow heart disorder in `Millionaire' was observed when `Fiesta' was used as the pollinizer.

SUMMARYA reliable evaluation of crop nutritional status is crucial for supporting fertilization aiming at maximizing qualitative and quantitative aspects of production and reducing the environmental impact of cropping systems. Most of the available simulation models evaluate crop nutritional status according to the nitrogen (N) dilution law, which derives critical N concentration as a function of above-ground biomass. An alternative approach, developed during a project carried out with students of the Cropping Systems Masters course at the University of Milan, was tested and compared with existing models (N dilution law and approaches implemented in EPIC and DAISY models). The new model (MAZINGA) reproduces the effect of leaf self-shading in lowering plant N concentration (PNC) through an inverse of the fraction of radiation intercepted by the canopy. The models were tested using data collected in four rice (Oryza sativaL.) experiments carried out in Northern Italy under potential and N-limited conditions. MAZINGA was the most accurate in identifying the critical N concentration, and therefore in discriminating PNC of plants growing under N-limited and non-limited conditions, respectively. In addition, the present work proved the effectiveness of crop models when used as tools for supporting education.

Due to the lack of viable pollen produced in seedless (triploid) watermelons, fruit set in seedless watermelons requires a standard seed (diploid) producing cultivar (hereafter referred to as a pollinizer) to be interplanted as a source of pollen. It is recommended that one row of pollinizer be planted for every two rows of seedless watermelon. There is little to no information available to growers comparing the effects of pollinizers on seedless watermelon yield and quality. We conducted a study to evaluate the effectiveness of three seeded pollinizers (`Crimson Sweet', `Fiesta', and `Royal Sweet') on yield and quality of four seedless watermelon hybrids (`Abbott and Cobb 5244', `Crimson Trio', `Millionaire', and `Tri-X 313'). `Royal Sweet' as a pollinizer tended to produce higher yields of small (<3.6 kg) and medium-sized seedless watermelons (3.6-7.3 kg) per acre compared to `Crimson Sweet' and `Fiesta'. `Crimson Sweet' produced a greater number of large (>7.3 kg) seedless watermelons compared to `Fiesta' and `Royal Sweet'. However, the number of marketable melons (>3.6 kg) did not differ among the three pollinizers evaluated. Two quality measurements taken (hollow heart and soluble sugars) were not influenced by the choice of pollinizer.