Growth and chloroplast ultrastructure of two citrus rootstock seedlings in response to ammonium and nitrate nutrition 1

Abstract

It is important to understand the differential response of citrus rootstock to various rates of nitrogen (N) forms in order to evaluate the tree response to N availability under different production conditions. In this study, the effects of N sources (NH₄‐N or NO₃‐N), and rates (5, 15, 45, and 135 mg N L^?1) on two citrus rootstock seedlings (Swingle citrumelo, SC; Cleopatra mandarin, CM) growth (110 d) and N concentrations in various parts of seedling were investigated in a nutrient solution experiment. The effects of N nutrition on the chloroplast ultrastructure of leaves were examined at the end of the experiment. Rootstock and N sources significantly influenced the growth of leaves, stems, and roots. The growth of all seedling parts of both rootstocks decreased with an increase in concentration of NH₄‐N in the solution. In contrast, there was a positive relationship between the seedling growth and the concentration of NO₃‐N in the nutrient solution with marked response observed as the NO₃‐N concentration increased from 5 to 15 mg L^?1 The experiment demonstrated a distinct growth suppression effect with an increase in concentration of NH₄‐N in the nutrient solution, particularly SC rootstock. Chloroplast ultra‐structure of the leaves showed evidence of injury of the seedlings which received N entirely as NH₄ ⁺ form, but the injury was not seen when the seedlings received N as the NO₃‐N form. The disruption of chloroplast ultrastructure increased with increased rate of NH₄‐N. The most conspicuous characteristic of ammonium toxicity was the massive accumulation of strands granules and phytoferritin which is clearly an evidence of NH₃ toxicity. The results are important for understanding the implications of N source on seedling growth and chloroplast structure of citrus leaves.     

Evaluation of Poultry Litter Amendment to Agricultural Soils: Leaching Losses and Partitioning of Trace Elements in Collard Greens

Water, Air, &; Soil Pollution - Leaching of trace metals and greenhouse plant growth (Collard greens; Brassica oleracea var. acephala) response studies were conducted in two types of soils with...     

Evaluation of capacitance probes for optimal irrigation of citrus through soil moisture monitoring in an entisol profile

 Continuous monitoring of soil moisture content within and below the rooting zone can facilitate optimal irrigation scheduling aimed at minimizing both the effects of water stress on the plants, and also the leaching of water below the root zone, which can have adverse environmental effects. The use of Sentek capacitance probes (EnviroSCAN RT5) in scheduling citrus irrigation was evaluated using 3-year-old Hamlin orange trees [Citrus sinensis (L.) Osb.] on Swingle citrumelo rootstock [Citrus paradisi Macf. × Poncirus trifoliata (L.) Raf.] grown in a Candler fine sand (hyperthermic, uncoated, Typic Quartzipsamments). Available soil moisture calculated according to capacitance probe readings of soil moisture agreed well with that calculated using soil water release curves determined in the laboratory. A utility program was developed to process the data collected by the capacitance probe into a spreadsheet format. Processed data were used to calculate soil water storage within and below the citrus root zone at desired time intervals. Irrigation set points (i.e., full point equivalent to maximum desirable water storage and refill points I and II) were defined based on field capacity determined both in the field and in the laboratory and permanent wilting point. It was possible to maintain the water content in the root zone between the full and refill points I and II during most of the growing season. Although soil water content in the root zone exceeded the full point during periods of high irrigation, it drained rapidly within 24–48 h after the end of such irrigation events. Using soil moisture depletion in the root zone during periods of low water application to estimate citrus evapotranspiration (ET), the calculated daily average ET during 10-day period in November was 1.33 mm day⁻¹. Received: 11 August 1998     

Nitrogen transformation from three soil organic amendments in a sandy soil

Abstract

A sandy soil was amended with various rates (20 – 320 g air-dry weight basis of the amendments per kg of air-dry soil) of chicken manure (CM), sewage sludge (SS), and incinerated sewage sludge (ISS) and incubated for 100 days in a greenhouse at 15% (wt/wt) soil water content. At the beginning of incubation, NH₄-N concentrations varied from 50 – 280 mg kg^?1 in the CM amended soil with negligible amounts of NO₃-N. Subsequently, the concentration of NH₄-N decreased while that of NO₃-N increased rapidly. In soil amended with SS at 20 – 80 g kg^?1 rates, the NO₃-N concentration increased sharply during the first 20 days, followed by a slow rate of increase over the rest of the incubation period. However, at a 160 g kg^?1 SS rate, there were three distinct phases of NO₃-N release which lasted for160 days. In the ISS amended soil, the nitrification process was completed during the initial 30 days, and the concentrations of NH₄-N and NO₃-N were lower than those for the other treatments. The mineralized N across different rates accounted for 20 – 36%, 16 – 40%, and 26 – 50% of the total N applied as CM, SS, and ISS, respectively.     

Irrigation water salinity affects soil nutrient distribution,root density,and leaf nutrient levels of citrus under drip fertigation 1

The purpose of this study was to determine the effects of irrigation water salinity on soil nutrient distribution, citrus leaf nutrition and root density. Irrigation water, salinized to an EC of about 0.3,1.6, or 2.5 dS/m using a 3:1 ratio of NaCl:CaCl₂ plus uniform weekly applications of liquid fertilizer, was applied through a drip system. Soil samples were taken at depths of 0–15 and 15–30 cm, both directly under the drippers and 45 cm outward from the drippers, near 8‐year old ‘Valencia’ orange trees on either Carrizo citrange or Sour orange rootstocks growing in a Candler fine sand in lysimeter tanks.

In both undisturbed and uniformly mixed soil profiles, soil pH and concentrations of Na, Ca, and P were higher under the dripper than 45 cm outward from the dripper at both depths regardless of salinity level. Soil N and Cl tended to be higher outward from the drippers than near the drippers, except in undisturbed soil at the 0–15 cm depth. Increasing salinity levels in the mixed soil profile not only increased soil EC, Na, Cl, and Ca, but also increased the concentration of P and decreased the concentration of Mg.

Root density of both rootstocks were increased by high salinity. Root densities and organic matter percentages were higher in soil sampled under drippers than that sampled outward from drippers. Leaf nutritional values and responses to salinity were dependent on rootstock as trees on sour orange had higher K and Ca, but lower Mg and Cl than trees on Carrizo. Although there were no nutrient deficiencies, K of trees on Carrizo citrange and Mg of trees on sour orange were rereduced by high salinity. An increase in leaf Ca concentrations when irrigated with salinized irrigation water likely minimized the effects of salt stress.