Growth dynamics and yield of melon as influenced by nitrogen fertilizer

Nitrogen (N) is an important nutrient for melon (Cucumis melo L.) production. However there is scanty information about the amount necessary to maintain an appropriate balance between growth and yield. Melon vegetative organs must develop sufficiently to intercept light and accumulate water and nutrients but it is also important to obtain a large reproductive-vegetative dry weight ratio to maximize the fruit yield. We evaluated the influence of different N amounts on the growth, production of dry matter and fruit yield of a melon ‘Piel de sapo’ type. A three-year field experiment was carried out from May to September. Melons were subjected to an irrigation depth of 100% crop evapotranspiration and to 11 N fertilization rates, ranging 11 to 393 kg ha –1 in the three years. The dry matter production of leaves and stems increased as the N amount increased. The dry matter of the whole plant was affected similarly, while the fruit dry matter decreased as the N amount was increased above 112, 93 and 95 kg ha –1 , in 2005, 2006 and 2007, respectively. The maximum Leaf Area Index (LAI), 3.1, was obtained at 393 kg ha –1 of N. The lowest N supply reduced the fruit yield by 21%, while the highest increased the vegetative growth, LAI and Leaf Area Duration (LAD), but reduced yield by 24% relative to the N93 treatment. Excessive applications of N increase vegetative growth at the expense of reproductive growth. For this melon type, rates about 90-100 kg ha –1 of N are sufficient for adequate plant growth, development and maximum production. To obtain fruit yield close to the maximum, the leaf N concentration at the end of the crop cycle should be higher than 19.5 g kg –1

Stopping power dependence of nitrogen sputtering yields in copper nitride films under swift-ion irradiation: Exciton model approach

Nitrogen sputtering yields as high as 104 atoms/ion, are obtained by irradiating N-rich-Cu3N films (N concentration: 33 ± 2 at.%) with Cu ions at energies in the range 10?42 MeV. The kinetics of N sputtering as a function of ion fluence is determined at several energies (stopping powers) for films deposited on both, glass and silicon substrates. The kinetic curves show that the amount of nitrogen release strongly increases with rising irradiation fluence up to reaching a saturation level at a low remaining nitrogen fraction (5?10%), in which no further nitrogen reduction is observed. The sputtering rate for nitrogen depletion is found to be independent of the substrate and to linearly increase with electronic stopping power (Se). A stopping power (Sth) threshold of ?3.5 keV/nm for nitrogen depletion has been estimated from extrapolation of the data. Experimental kinetic data have been analyzed within a bulk molecular recombination model. The microscopic mechanisms of the nitrogen depletion process are discussed in terms of a non-radiative exciton decay model. In particular, the estimated threshold is related to a minimum exciton density which is required to achieve efficient sputtering rates.

Nitrogen uptake dynamics, yield and quality as influenced by nitrogen fertilization in "Piel de sapo" melon.

The need to reduce nitrogen (N) fertilizer pollution strengthens the importance of improving the utilization efficiency of applied N to crops. This requires knowledge of crop N uptake characteristics and how fertilization management affects it. A three-year field experiment was conducted from May to September in central Spain to investigate the influence of different N rates, which ranged from 11 to 393 kg ha-1, applied through drip irrigation, on the dynamics of N uptake, nitrogen use efficiency (NUE), fruit yield and quality of a ?Piel de sapo? melon crop (Cucumis melo L. cv. Sancho). Both N concentration and N content increased in different plant parts with the N rate. Leaves had the highest N concentration, which declined by 40-50% from 34-41 days after transplanting (DAT), while the highest N uptake rate was observed from 30-35 to 70-80 DAT, coinciding with fruit development. In each year, NUE declined with increasing N rate. With N fertilizer applications close to the optimum N rate of 90-100 kg ha-1, the fruits removed approximately 60 kg N ha-1, and the amount of N in the crop residue was about 80 kg N ha-1; this serves to replenish the organic nutrient pool in the soil and may be used by subsequent crops following mineralization.

Impact of nitrogen uptake on field water balance in fertirrigated melon.

Agronomic management in Ciudad Real, a province in central Spain, is characteristic of semi-arid cropped areas whose water supplies have high nitrate (NO3?) content due to environmental degradation. This situation is aggravated by the existence of a restrictive subsurface layer of ?caliche? or hardpan at a depth of 0.60 m. Under these circumstances, fertirrigation rates, including nitrogen (N) fertilizer schedules, must be carefully calibrated to optimize melon yields while minimizing the N pollution and water supply. Such optimization was sought by fertilizing with different doses of N and irrigating at 100% of the ETc (crop evapotranspiration), adjusted for this crop and area. The N content in the four fertilizer doses used was: 0, 55, 82 and 109 kg N ha?1. Due to the NO3? content in the irrigation water, however, the actual N content was 30 kg ha?1 higher in all four treatments repeated in two different years. The results showed correlation between melon plant N uptake and drainage (Dr), which in turn affects the amount of N leached, as well as correlation between Dr and LAI (leaf area index) for each treatment. A fertilizer factor (?) was estimated through two methods, from difference in Dr and in LAI ratio with respect to the maximum N dose, to correct ETc based on N doses. The difference was found in the adjusted evapotranspiration in both years using the corresponding ? achieved 42?49 mm at vegetative period, depending on the method, and it was not significant at senescent period. Finally, a growth curve between N uptake and plant dry weight (DW) for each treatment was defined to confirm that the observed higher plant vigour, showing higher LAI and reduced Dr, was due mainly to higher N doses.

Biogeochemical indicators of elevated nitrogen deposition in semiarid Mediterranean ecosystems

Nitrogen (N) deposition has doubled the natural N inputs received by ecosystems through biological N fixation and is currently a global problem that is affecting the Mediterranean regions. We evaluated the existing relationships between increased atmospheric N deposition and biogeochemical indicators related to soil chemical factors and cryptogam species across semiarid central, southern, and eastern Spain. The cryptogam species studied were the biocrust-forming species Pleurochaete squarrosa (moss) and Cladonia foliacea (lichen). Sampling sites were chosen in Quercus coccifera (kermes oak) shrublands and Pinus halepensis (Aleppo pine) forests to cover a range of inorganic N deposition representative of the levels found in the Iberian Peninsula (between 4.4 and 8.1 kg N ha(-1) year(-1)). We extended the ambient N deposition gradient by including experimental plots to which N had been added for 3 years at rates of 10, 20, and 50 kg N ha(-1) year(-1). Overall, N deposition (extant plus simulated) increased soil inorganic N availability and caused soil acidification. Nitrogen deposition increased phosphomonoesterase (PME) enzyme activity and PME/nitrate reductase (NR) ratio in both species, whereas the NR activity was reduced only in the moss. Responses of PME and NR activities were attributed to an induced N to phosphorus imbalance and to N saturation, respectively. When only considering the ambient N deposition, soil organic C and N contents were positively related to N deposition, a response driven by pine forests. The PME/NR ratios of the moss were better predictors of N deposition rates than PME or NR activities alone in shrublands, whereas no correlation between N deposition and the lichen physiology was observed. We conclude that integrative physiological measurements, such as PME/NR ratios, measured on sensitive species such as P. squarrosa, can provide useful data for national-scale biomonitoring programs, whereas soil acidification and soil C and N storage could be useful as additional corroborating ecosystem indicators of chronic N pollution.