Effects of Time of Nitrogen Application and Soil Texture on the Availability of Isotopically Labeled Fertilizer Nitrogen to Reproductive and Vegetative Tissue of Mature Almond Trees

Abstract

Mature almond [Prunus dulcis (Mill) D.A. Webb] trees growing on light-(Delhi sand) and heavy-textured (Yolo silty clay loam) soils were fertilized with 15N-depleted ammonium sulfate at different times during the year to permit direct measurement of fertilizer N within the trees. The distribution of fertilizer N between vegetative and reproductive organs was monitored during both the year of application, 1980, and the subsequent year. The later that fertilizer N was applied during the season, the less fertilizer N was recovered in the fruit and leaves that year, and the greater its N contribution to these organs was the following year. Isotopic labeling of fruit and leaves appeared to be relatively unaffected by soil texture during the year of fertilizer application. During the subsequent year, however, the recovery of fertilizer N by fruit and leaves was 2-fold greater on the heavy-textured soil than on the light-textured soil. Recovery of labeled N in fruit was relatively low on both soil types following application of fertilizer during the dormant period. Isotopic N was recovered in fruit in both 1980 and 1981 and constituted about 20% to 28% of fruit N at most. About 25% of the applied N was removed in the fruit on the heavy-textured soil over a 2-year period. Up to 1 kg N per tree was removed annually in the harvested fruit.

Distribution and Translocation of Nitrogen Absorbed During Late Spring by Two-Year-Old Grapevines Grown in Sand Culture

“…At the first sampling date, the shoots, leaves, and bunches contained a higher concentration of labeled N than the permanent parts (Table 3). Similar results were obtained for citrus (8,14) while N absorbed during spring by almond was also preferentially translocated to vegetative growth (27). The ~SN concentration in the total N (TN) fraction of the permanent parts was reduced as the season progressed, and at the end of leaf-fall the fine roots, rootstock-and scion trunks reached a comparable value of ca 0.24 atom % excess ~SN.…”

“…Furthermore, the growth pattern of the grapevine differs from that of most other deciduous fruits on account of the period of bloom occurring six to eight weeks after budbreak, whereas for other fruit crops, blossoms are the first organs signifying the end of dormancy. This is probably the reason why such a high proportion of labeled N was recovered in the bunches, whereas for almond, soil-derived fertilizer N is preferentially translocated to vegetative growth in the year of application (27). The distribution of labeled N be-tween bunches, shoots, and leaves, as found in the current trial, was comparable to that found for springapplied N in a field trial on a sandy soil with a low Nsupplying capacity (7).…”

“…This shows that reserve N accumulated during spring was still actively utilized one year after absorption. For almonds, the reproductive organs were also found to be highly dependent on the endogenous pool of stored N during the early developmental stages (27) Permanent wood: For the permanent wood, i.e., rootstock-and scion trunks, dry mass increased as expected (2,5) from the end of rapid shoot growth to the start of leaf-fall (Fig. 2a, 2b).…”

Growth of ‘Thompson Seedless’ Grapevines: II. Nitrogen Distribution

“…However, the amount of N found in clusters during 1985 may be a direct consequence of N fertilization in Spring 1984. It has been demonstrated that soil-derived fertilizer N preferentially was partitioned to the vegetative structures of mature almond trees the year N was applied and then recycled to the fruit the subsequent year (19). While the soil N status of the vineyard used in this study was unknown, it appeared that it may have been adequate to provide the necessary N required for vine growth under conditions of the experiment prior to N fertilization in 1984, as dry weights and yield were not appreciably different before then (21).…”

Translocation of Foliar-applied Urea 15N to Reproductive and Vegetative Sinks of Avocado and Its Effect on Initial Fruit Set

“…All plants are dependent on soil-derived N for maintenance of vegetative growth and completion of the reproductive cycle. When N uptake from the soil is insufficient to satisfy the requirement for growth, woody species, unlike herbaceous plants, can draw on internal pools of N stored within perennial tissues (14,17,22,24,26,28). Deciduous trees store sufficient N in their shoots, trunk, and roots to support the initial reproductive and vegetative growth (14,22,24,25,28).…”