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A spring application of 19 g CO(15NH2)2/plant at 2.49% atom percent enrichment was made in Mar. 1995 on 2-year old, field-grown `Arapaho' blackberry plants. Individual plants were harvested during the study at preharvest (late May), postharvest (mid-July), and early dormancy (late October). The following plant parts were separated for analysis: roots, primocanes, floricanes, primocane leaves, floricane leaves, fruits. Soil samples were also taken from within the drip line of the plants at each sample date. Plant tissues were washed, dry weights measured and ground for acid digestion, total N determination and 15N analysis. Samples were measured for 15N atom percent abundance by a isotope ratio spectrometer. The whole-plant dry matter in creased during the season from 53 g in May to 153 g in October. Plants sampled in October had a greater amount of dry matter in roots than in any other tissue. There was a decreased total N content in all vegetative tissues (leaves and canes) from May to October. The maximum fertilizer 15N percent recovery was 43% (October) and the minimum was 12% (May) from the total plant tissues. Compared to other plant tissues, floricane leaves and primocanes recovered significantly more fertilizer 15N in May, while roots and primocane leaves recovered more in October. Floricanes and fruits did not increase in 15N levels during the sampling period. Fertilizer 15N recovered in the soil amounted to 35.5% of the applied with 4.5% found in the inorganic fraction, 31% in the organic fraction. There were no statistical differences in percent recovery of the fertilizer 15N among sample dates in the topsoil. October 15N percent recovery was much lower than May in the subsoil, indicating a downward movement of N by leaching. Averaging all sample dates, 59.5% of the labeled fertilizer was accounted for in the plant and soil, with the remaining portion probably lost via volatilization, leaching, and/or denitrification.
A planting of sawdust-mulched highbush blueberries (cv. Bluecrop) was established on a Captina silt loam at the Univ. of Arkansas Research and Extension Center, Fayetteville, in 1994. Nitrogen rate and method of delivery treatments were begun that year and continued through the first two fruiting years (1996 and 1997). Rates included 0, 67, 134, 201, and 268 kg·ha-1 N using ammonium sulfate during the fruiting years (one-half and two-thirds these rates in 1994 and 1995, respectively), and methods of delivery included dry, surface-applied, and fertigation. Total N for the year was applied in three applications for the dry application and in 12 applications using fertigation. Neither yield nor berry mass were statistically significantly affected by N rate or method of delivery. Also, method of delivery had little effect on foliar levels of any macro- and microelements. Rate of N influenced foliar N most years, with the highest N rate increasing foliar N the greatest. The N rate required to consistently achieve adequate foliar N levels (minimum of 1.6% N) was 134 kg·ha-1. Foliar levels >2.0% were common with the two highest N rates. Foliar Mg and Mn were also influenced by N rate, with the lowest Mg level found for the highest N rate, while excess foliar Mn (800 to 100 ppm) was common with the higher N rates in 1997.
Three studies were established to compare spring (S) vs. autumn (F) N fertilizer applications on apple tree performance. The studies used newly planted trees, 4-yr-old trees, and 8-yr-old trees, fertilized with either ammonium nitrate or urea at 2 weeks after harvest (F) or at bud break (S). In the first 3 years growth in a newly planted orchard, time of fertilizer did not significantly affect tree height or TCSA. In the first cropping year, F fertilized trees had the greatest flower cluster number and bloom density but similar % set and yield compared to S fertilized trees. F fertilized trees in mature orchards studies tended to be shorter and have smaller TCSA increment after 3 yrs. Treatments did not affect bloom density, % set or total yield although spring fertilized trees had a greater % drop. Although spur leaves of F fertilized trees had greater N content at bloom, shoot leaves typically had lower N and Mn, and higher P, K, and Ca at 90 days after bloom compared to S treatment trees.