Early spring growth of perennial strawberry (Fragaria ×ananassa Duch.) plants is supported by the carbohydrate and nitrogen (N) reserves accumulated from the previous growing season. The limitations of these reserves on the initial spring growth and yield of perennial strawberries have not been studied in detail, particularly the influence of N reserves. Differential N fertigation (0 to 20 mm N) was applied to potted strawberries during the growing season and a supplemental foliar urea application was applied to a portion of the plants in the fall to modify reserve N during dormancy. Plant N content and spring vegetative growth the year after fertigation increased nearly twofold with increasing N fertigation. Photosynthesis per unit leaf area also increased up to 10 mm of fertilizer N and then stabilized through 20 mm. Foliar urea application in fall further increased total plant N content and size, decreased carbohydrate concentration, and also decreased yield in plants with the most total N. Nitrogen fertigation was resumed on a portion of these plants in early spring, but new growth and subsequent yield were unaffected by spring N application. In a second experiment, CO2 enrichment with and without soil and foliar N application in the fall was used to vary carbon (C) and N reserves. CO2 enrichment in fall increased plant size and yield the next July by ≈20%, but total nonstructural carbohydrate and N concentrations were unaffected. Foliar urea application also increased N and C reserves (but not concentration) as well as yield in both enriched and unenriched plants. Although foliar urea in fall decreased carbohydrate concentration, total reserve levels were unaffected because treated plants were larger. In this experiment, spring N increased plant size by ≈50%, but yield was increased only 12%, suggesting that yields are mostly dependent on reserves. Increasing N reserves with a late fall foliar application is one strategy growers can use to efficiently enhance growth and yield in low to moderately fertilized plants.
Laura Elisa Acuña-Maldonado and Marvin P. Pritts
Laura Elisa Acuña-Maldonado, Michael W. Smith, Niels O. Maness, Becky S. Cheary, Becky L. Carroll, and Gordon V. Johnson
Nitrogen was applied to mature pecan (Carya illinoinensis Wangenh. C. Koch.) trees annually as a single application at 125 kg·ha-1 N in March or as a split application with 60% (75 kg·ha-1 N) applied in March and the remaining 40% (50 kg·ha-1 N) applied during the first week of October. Nitrogen treatment did not affect yield, and had little effect on the amount of N absorbed. Nitrogen absorption was greater between budbreak and the end of shoot expansion than at other times of the year. Substantial amounts of N were also absorbed between leaf fall and budbreak. Little N was absorbed between the end of shoot expansion and leaf fall, or tree N losses met or exceeded N absorption. Pistillate flowers and fruit accounted for a small portion of the tree's N; ≈0.6% at anthesis and 4% at harvest. The leaves contained ≈25% of the tree's N in May and ≈17% when killed by freezing temperatures in November. Leaves appeared to contribute little to the tree's stored N reserves. Roots ≥1 cm diameter were the largest site of N storage during the winter. Stored N reserves in the perennial parts of the tree averaged 13% of the tree's total N over a three year period. Current year's N absorption was inversely related to the amount of stored N, but was not related to the current or previous year's crop load.