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The response of 11 different varieties of grapes treated with different levels of N was studied over a seven-year period Phosphorau fertilizer was applied midway through the study. Tissue samples were tested for total P and NO₃-N content, and yield determined annually. The results showed a positive interaction in tens of increased yield between N and P when sufficient quantities of both nutrients were provided

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The relationships between increasing nitrogen fertilization and growth, maximum CO₂ assimilation and the initial slope of the CO₂ response curve were studied in two ecotypes of wild strawberry, Fragaria chiloensis (L) Duchn. Nitrogen accumulation of CA11, an ecotype from a low -nutrient dune site, was greater at all nitrogen concentrations than that of RCP37, an ecotype from a higher- nutrient strand site. Maximum CO₂ assimilation, total Rubisco activity, dry weight, and initiation of leaves and crowns were higher in CA11 than RCP37 as nitrogen treatment was increased from 0 to 200 mg l⁻¹, whereas these parameters were lower in CA11 when fertilized at 300 mg l⁻¹, but not in RCP37. The mean leaf area of CA11 was greater than RCP37 when grown with no supplemental nitrogen, but mean leaf area of the two lines was similar under nitrogen fertilization. Maximum CO₂ assimilation and carboxylation efficiency increased with increasing leaf nitrogen in both clones. At equivalent concentrations of leaf nitrogen, RCP37 had higher CO₂ assimilation and carboxylation efficiency than CA11 and the difference between the 2 clones increased as leaf nitrogen increased. Thus, RCP37 had a higher photosynthetic nitrogen use efficiency than CA11. However, at a given applied nitrogen level, CA11 allocated more nitrogen to a unit of leaf area so that photosynthetic rates were higher than RCP37, except at the highest application of 300 mg l⁻¹. The high nitrogen accumulation capacity and resource allocation to fruiting structures (crowns) in CA11 lead us to suggest that this clone may possess genes that could increase fruit yield in cultivated strawberry.

Revised; Originally Published: 2006 / 3 pp.