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Simulating Infertile Acid Soils with Nutrient Solutions

The Effects on Brachiaria Species

^a Centro Internacional de Agricultura Tropical (CIAT), A.A. 6713 Cali, Colombia
^b Institut für Ökologie und Naturschutz, Universität Wien, Althanstraße 14, A-1090 Wien, Austria
^c Center for the Application of Molecular Biology to International Agriculture (CAMBIA), GPO Box 3200 Canberra, ACT 2601, Australia

View larger version (22K): [in a new window]   Fig. 1. Nitrogen mineralization and pH changes in soil solutions. The (A) pH and (B) concentrations of NO-3 and (C) NH+4 were determined in soil solutions extracted from soil samples of sandy loam and clay loam (incubated for up to 64 d after rewetting).

View larger version (27K): [in a new window]   Fig. 2. Relationship between the concentrations of NO-3 and cations in soil solutions extracted from soil samples of sandy loam and clay loam (incubated for up to 64 d after rewetting). The dotted line designates a hypothetical equimolar ratio between the two.

View larger version (37K): [in a new window]   Fig. 3. Activities of major cations (Ca2+, Mg2+, K+, Na+) and anions (SO-4, Cl-) in soil solutions extracted from soil samples of sandy loam and clay loam (incubated for up to 64 d after rewetting). Activities were plotted against that of NO-3, which increased substantially during nitrification. Dotted lines indicate the activities of the same ions in the four designed treatments for comparison (AN ± Al, LN ± Al).

View larger version (27K): [in a new window]   Fig. 4. Solubilities of Al and phosphate in soil solutions as a function of pH. The activities of Al3+ and H2PO-4 in soil solutions extracted from soil samples of sandy loam and clay loam (incubated for up to 64 d after rewetting) were plotted against soil-solution pH. Lines show the upper solubility limits of crystalline gibbsite and variscite in equilibrium with gibbsite. Data points within dotted ellipses are from soil solutions extracted 1 d after the soil samples were rewetted. Because of the limited sensitivity of the colorimetric assay used to quantify Alinorg, only {Al3+} values greater than 1 µM are shown in the top plot.

View larger version (35K): [in a new window]   Fig. 5. Growth-inhibitory effect of the nutrient solution simulating chemical properties of infertile acid soils (LN + Al). Signalgrass and ruzigrass were grown in the greenhouse (left panel) and growth chamber (right panel). Growth was measured relative to the Al-free reference treatment containing adequate nutrient levels (i.e., [LN + Al]/AN). Values of growth parameters for plants from the AN treatment in the greenhouse were: 125.8 mg (shoot dry weight, SDW), 26.3 mg (root dry weight, RDW), 40.5 cm2 (leaf area, LA), and 12.1 m (root length, RL) for signalgrass, and 139.3 mg (SDW), 40.5 mg (RDW), 52.5 cm2 (LA), and 18.8 m (RL) for ruzigrass. Corresponding values in the growth chamber were: 47.5 mg (SDW), 5.3 mg (RDW), 23.4 cm2 (LA), and 1.43 m (RL) for signalgrass, and 76.0 mg (SDW), 9.8 mg (RDW), 39.9 cm2 (LA), and 2.81 m (RL) for ruzigrass. Error bars designate standard errors computed by weighted jackknifing, and asterisks indicate statistically significant differences between the grasses (P < 0.05).

View larger version (32K): [in a new window]   Fig. 6. Interaction between the effects of Al toxicity and nutrient deficiency on root architecture of plants grown in the greenhouse. The images display primary root systems of plants grown under adequate (AN) and low (LN) nutrient supply and in the presence or absence of Al.

View larger version (38K): [in a new window]   Fig. 7. Aluminum resistance of signalgrass and ruzigrass and its dependence on nutrient concentrations in the growth medium. Resistance to Al was measured at (A) low and (B) adequate nutrient supply, by quantifying its effect on plant growth relative to the corresponding Al-free treatment ([LN + Al]/LN and [AN + Al]/AN, respectively). Values of growth parameters for plants from the LN treatment in the greenhouse were 47.3 mg (shoot dry weight, SDW), 18.3 mg (root dry weight, RDW), 15.3 cm2 (leaf area, LA), and 5.98 m (root length, RL) for signalgrass, and 52.8 mg (SDW), 22.7 mg (RDW), 19.1 cm2 (LA), and 5.92 m (RL) for ruzigrass. Corresponding values in the growth chamber were 34.5 mg (SDW), 6.2 mg (RDW), 13.8 cm2 (LA), and 1.15 m (RL) for signalgrass, and 58.3 mg (SDW), 11.8 mg (RDW), 21.2 cm2 (LA), and 1.89 m (RL) for ruzigrass. The values for plants from the AN treatment are listed in the legend to Fig. 5. Error bars designate standard errors computed by weighted jackknifing, and asterisks indicate statistically significant differences between the two grasses (P < 0.05).

View larger version (26K): [in a new window]   Fig. 8. Mineral composition of shoots of plants grown at two levels of nutrient supply in the presence of Al (AN + Al and LN + Al treatments). Nutrient concentrations are shown in grams per kilogram (g kg-1) of dry weight. Numbers designate the maximum values of the scales of five different axes, each used to plot the concentration of a single nutrient. Asterisks indicate statistically significant differences between the two treatments (P < 0.05).