Sandy, infertile soils can benefit from the addition of organic waste amendments. Annual applications of organic wastes for as long as 4 yr increased soil organic matter content, decreased soil bulk density, and increased soil water retention of a coarse-textured soil. However, soil water-holding capacity was not necessarily increased, and there was a limited effect on soil cation exchange capacity. Key words: Cation exchange capacity, water retention, soil pH, soil organic matter, soil bulk density
Additional index words. Malus ×domestica, drip-fertigation, ground cover, soil man age ment Abstract. 'Spartanʼ apple (Malus ×domestica Borkh.) trees on M.9 (T337) root stock were planted in April 1994 at 1.25 m × 3.5 m spac ing. Seven soil management treat ments were applied within a 2-m-wide strip cen tered on the tree row and arranged in a randomized complete-block experimental de sign. Treat ments included a weed-free strip (check) maintained with four annual ap pli ca tions of glyphosate; surface ap pli ca tion of 45 t·ha -1 of Greater Vancouver Re gion al District (GVRD) biosolids applied in 1994 and again in 1997; mulches of shred ded offi ce paper; alfalfa (Medicago sativa L.) hay; black wo ven polypro py lene; and shredded paper applied over 45 t·ha -1 GVRD-and Kelowna-biosolids applied in 1994 and 1997. All ex per i men tal trees were fertigated with phos pho rus (P) in the fi rst year and with ni tro gen (N) annually. Cu mu la tive yield for the fi rst fi ve harvests was higher for trees sub ject ed to any soil man age ment treatment relative to check trees. Max i mum cu mu la tive yield, exceeding check trees by 80%, was measured for trees grown with a shred ded paper mulch with or without biosolids application. Trees from the three shredded paper treatments were the only ones sig nifi cant ly larger than check trees after six grow ing seasons. No in creas es in leaf nutrient concentration were con sis tent ly as so ci at ed with improved tree per for mance. Notable effects included in creased leaf P con cen tra tion associated with biosolids application, increased leaf K con cen tra tion after alfalfa mulch application and temporary in creas es in leaf Zn and Cu concentration associated with application of biosolids high in Zn and Cu. Use of both mulches and biosolids amendments ben e fi ts growth of trees in high density plantings de spite daily drip irrigation and annual fertigation. Nonsignifi cant or signifi cant at P ≤ 0.05, 0.01, 0.001, or 0.0001, re spec tive ly.
Elstar apple trees (Malus domestica Borkh.) on M.9 rootstock received either 5 or 35 g N tree(-1) year(-1) during the first two growing seasons after planting, applied as Ca(NO(3))(2) on a daily basis for nine weeks through a drip irrigation system. During the third growing season (1994), all trees were treated with 20 g N tree(-1) year(-1) as (15)NH(4) (15)NO(3) with applications starting on April 22 and continuing for 10 weeks. Soil solution nitrate-N and ammonium-N were monitored weekly with suction lysimeters located 30 cm beneath the drip emitters. Spur and shoot leaves were sampled intensively from full bloom to the end of rapid shoot growth. During the period of nitrogen application, soil solution nitrate-N and ammonium-N were relatively constant, at about 24 and 1.0 mg l(-1) respectively. Growth of the spur leaves was completed by one week after full bloom (May 12), whereas biomass of the shoot leaves increased until mid-June. Nitrogen for growth of the spur leaves was supplied mainly from remobilization, which was dependent on previous N supply. Accumulation of fertilizer N in spur leaves was independent of previous N treatments and continued until the end of the monitoring period (June 24), but contributed only 13% to total spur leaf N. Nitrogen for shoot leaf growth was independent of previous N treatments and was initially supplied primarily by remobilization, but by the end of extension growth, fertilizer N contributed 48% to total shoot leaf N. Linear increases in leaf N uptake throughout the period of rapid shoot growth and the large contribution of fertilizer N to total shoot leaf N were attributed to the constant supply of N available in the root zone through daily N fertilization.
Environmentally sound management of N in apple orchards requires that N supply meets demand. In 1997, newly planted apple trees (Malus domestica Borkh. var. Golden Delicious on M.9 rootstock) received daily applications of N for six weeks as Ca(15NO3)(2) through a drip irrigation system at a concentration of 112 mg l(-1) at 2-8, 5-11 or 8-14 weeks after planting. Irrigation water was applied either to meet estimated evaporative demand or at a fixed rate. In 1997, trees were harvested at 5, 8, 11 and 14 weeks after planting; and in 1998 at 3 weeks after full bloom. The amount of fertilizer N recovered was similar in trees in both irrigation treatments, but efficiency of fertilizer use was greater for trees receiving demand-controlled irrigation than fixed-rate irrigation. This was attributed to lower N inputs, greater retention time in the root zone and less N leaching in the demand-controlled irrigation treatments compared with fixed-rate irrigation treatments. Less fertilizer N was recovered by trees receiving an early application of N than a later application of N and this was related to the timing of N supply with respect to tree demand. Demand for root-supplied N was low until 11 weeks after planting, because early shoot and root growth was supported by N remobilized from woody tissue, which involved 55% of the total tree N content at planting. Rapid development of roots > 1 mm in diameter occurred between 11 and 14 weeks after planting, after remobilization ended, and was greater for trees receiving an early application of N than for trees receiving a later application of N. Late-season tree N demand was supplied by native soil N, and uptake and background soil solution N concentrations were higher for trees receiving demand-supplied irrigation compared with fixed-rate irrigation. Total annual N uptake by roots was unaffected by treatments and averaged 6-8 g tree(-1). Nitrogen applications in 1997 affected growth and N partitioning in 1998. Trees receiving early applications of N had more flowers, spur leaves and bourse shoots than trees receiving later applications of N. Consequently, more N was remobilized into fruits in trees receiving early applications of N compared with fruits in trees receiving later applications of N. Demand for N in the young apple trees was low. Early season demand was met by remobilization from woody tissues and the timing of demand for root-supplied N probably depends on whether flowering occurs. Method of N delivery affected the efficiency of N use. We conclude that N demand can be met at soil solution N concentrations of around 20 mg l(-1).
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