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In the southwestern and western Cotton Belt of the U.S. soil salinity can reduce cotton productivity and quality. This study was conducted to determine the physiological responses of six genotypes including five Upland cotton (Gossypium hirsutumL.) cultivars and one Pima cotton line (G. barbadenseL.) to NaCl under greenhouse conditions. Seeds were germinated and grown for 14 days prior to salt treatment (daily 100 ml of 200 mM NaCl) for 21 days. Compared with the control (daily 100 ml tap water), the NaCl treatment significantly reduced plant height, leaf area, fresh weight, and dry weight. The NaCl stress also significantly increased leaf chlorophyll content, but did not affect leaf fluorescence. Of the six genotypes, Pima 57-4 and SG 747 had the most growth reduction, and were most sensitive to NaCl; DP 33B, JinR 422 and Acala Phy 72 had the least growth reduction and were most NaCl tolerant. Although all the six genotypes under the salt treatment had significantly higher Na and Cl accumulation in leaves, SG 747 and Pima 57-4 accumulated more Na and Cl than DP 33B. Increases in leaf N, Zn, and Mn concentrations were also observed in the NaCl-treated plants. While leaf P, Ca, and S concentrations remained unchanged overall in the genotypes tested, leaf K, Mg, Fe, and Cu concentrations significantly decreased during salt stress. Reduction in plant height is a simple, easy, sensitive, non-destructive measurement to evaluate salt tolerance in cotton.

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An experiment was conducted to determine values for the mineralization potential (No), rate constant (k), and rate of mineralization for soils freshly amended with sewage sludge, and to determine the influence of soil type and sludge rate on these values. A secondary objective was to determine if the sum of two exponential functions could better model N mineralization than a single exponential functions, as is normally used. A clayey soil (Glendale, a Typic Torrifluvent) and a sandy soil (Latene, a Typic Calciorthid) were amended with three rates (0, 15, and 30 g kg−1) of gamma irradiated, dried, anaerobically digested sewage sludge. The Glendale soil was mixed with sand (1:1 by weight) to increase aeration. Triplicate 80‐g samples of each soil mixture were incubated aerobically for 32 weeks at 0.01 MPa moisture tension and 35°C. Before incubation and periodically during incubation, the soils were leached with 0.01M CaCl2 and the leachate analyzed for NH+4, NO‐2, and NO‐3. No and k were estimated by a nonlinear least squares iterative statistical method. Cumulative (NO‐3 + NO‐2)‐N at the end of 32 weeks was dependent on sludge rate, but not on soil type or the soil type‐sludge rate interaction. Cumulative (NO‐3 + NO‐2)‐N for the 0, 15, and 30 g kg−1 treatments were 60.9, 137.4, and 182.6 mg (NO‐3 + NO‐2)‐N kg−1, respectively. Mineralization rates decreased rapidly the first two weeks, followed by a slower decrease with time. Rates were higher in sludge‐amended soil than in unamended soil and averaged 0.6, 1.8, and 2.2 mg (NO‐3 + NO‐2)‐N kg−1 week−1 for the 0, 15, and 30 g kg−1 treatments, respectively, after 32 weeks. Several methods of estimating No and k were attempted. The best estimates for sludge‐amended soil were obtained by modelling N mineralization as the sum of two exponentials. Total N mineralization (organic N loss, x̄ (mean) = 63%) was more than twice that of net N mineralization (NO‐3 + NO‐2‐N accumulated, x̄ = 27%). Total and net mineralization were greater in the Glendale soil (x̄ = 68% and 30%, respectively) than in the Latene soil (x̄ = 58% and 24%, respectively). Total mineralization increased with sludge addition, but net mineralization decreased with sludge addition. Denitrification losses probably accounted for the discrepancies between total and net mineralization. Denitrification increased with sludge addition and was greater in the Glendale than the Latene soil.

The objective of this study was to investigate the influence of root temperature, Rhizobium japonicum strain, host variety, and plant age on soybean growth, nodulation, and N2 fixation.Soybean plants were grown in sand‐filled Leonard jars and watered with N‐free nutrient solution. Soybean root temperatures were held constant at 15, 20, 25, and 30°C in a growth chamber environment. At harvest, plant height and weight, nodule number and weight, and acetylene reduction activity were measured.Interactions between root temperature, R. japonicum strain, and soybean variety were complex and changed with plant age. Temperature by strain interactions were more common than temperature by variety, variety by strain, or temperature by variety by strain interactions. Plant height was solely dependent on root temperature, but nodulation and acetylene reduction activity parameters depended on temperature, strain, and variety. Such interactions were more complex at later growth stages.Maximum plant dry weight and nodule number occurred at 25°C. Nodule weight and acetylene reduction activity were greater at 25°C than at the other root temperatures early in plant growth (3–4 weeks after planting.) However, 5–6 weeks after planting, these parameters were greater at 20° than at 25°C. Apparently more nodules were formed at 25°C, but eventual nodule development, size and acetylene reduction activity was greater at 20°C. Nodules also degenerated sooner at 25°C. Nitrogen fixation significantly increased plant growth over that of the uninoculated controls except at 15°C. The confined root environment of the Leonard jar may have restricted further nodulation after 5 weeks from planting and may have influenced nodule weight and acetylene reduction activities as well as nodule numbers.