A B S T R A C TNear infiared rej7ectance ( N I R ) spectroscopy is a rapid, cheap, simple technique which can be used to make quantitative analyses of the concentrations of nutrients in plant tissue. The application of N I R to determine nitrogen in rice was examined. The absorbance spectrum of rice (Oryza sativa L ) shoot tissue was similar to that of the temperate cereal wheat even though rice tissue has a much higher silica content.A 19-filter N I R instrument was calibrated to estimate the nitrogen content of rice shoots with between 0.8 and 3.50% N by the Kjeldahl technique. The calibration model developed used three wavelengths to account for 96% qf the variation in sample Kjeldahl nitrogen concentrution. This model was validated using 67 samples comprising five rice varieties grown on farms in two seasons in southern New South Wales. The standard error of prediction of the model was 0.15% N . A tissue testing service using this N I R calibration is now operational for rice crops in southern New South Wales.
The early growth of wheat was compared under direct drilled (DD) and cultivated treatments at 21 farm sites throughout southern New South Wales in 1997, 7 sites in 1998, and 11 sites in 1999. The experiments investigated the involvement of (1) paddock history/management, (2) common soil-borne fungal pathogens, and (3) populations of various microbial groups in early growth reductions associated with DD. Cultivation increased early vegetative growth at 62% of sites with an average increase in dry matter production of 33% compared with DD plots. Reduced shoot growth under DD was closely associated (r = 0.899) with decreased development of the root system. Early growth reductions under DD did not appear related to management practices such as different sowing points, herbicide or fertiliser application, or soil pH and fertility. Soil type and previous crop species, however, influenced the incidence but not severity of early growth reductions. Reduced growth under DD was not associated with the presence of any of the common soil-borne fungal pathogens of wheat, or with rhizosphere populations of total aerobic bacteria, total fungi, aerobic spore-forming bacteria, Gram-negative bacteria, and actinomycetes. On average, Pseudomonas populations in the rhizosphere of seedlings grown in cultivated soil were reduced by 61% compared with the DD treatment at sites where early growth reductions under DD were evident. An assessment of the inhibitory activity of pseudomonads towards wheat seedlings in a test-tube bioassay indicated that reduced growth in DD plots was more closely related with the inhibitory activity of Pseudomonas spp. to root growth than their population in the rhizosphere. A close relationship existed between the inhibitory activity of Pseudomonas spp. isolated from each site and the response of wheat seedlings to cultivation (r = 0.865). These results suggest that Pseudomonas spp. with inhibitory activity to root growth are involved in the reduced early growth of DD wheat in southern New South Wales.
Wheat seedlings were grown in intact cores of soil removed from 26 sites throughout southern New South Wales where slower seedling growth in direct-drilled (DD) soil than in cultivated soil had been commonly reported. Experiments were conducted in a controlled environment using soil cultivation and fumigation to assess the role of physical and biological constraints to growth under direct drilling. Populations of various microbial groups (especially Pythium and Pseudomonas spp.) were assessed for their involvement in the growth reductions. Soil cultivation increased the growth of seedlings relative to the DD treatment in cores from 18 of the 26 sites (mean increase 43%), while sterilisation increased growth in DD cores from 25 of the sites (mean increase 68%). The growth response to cultivation was less than that to sterilisation in cores from most sites, suggesting that cultivation only partially removes the growth limitation. With the exception of one site, cultivating sterilised cores provided no additional growth benefits over the sterilised DD treatment, indicating that biological rather than physical factors per se were predominantly responsible for the reduced growth. The reduced growth in DD cores was not associated with the presence of any of the common soil-borne fungal pathogens of wheat. Averaged across sites, Pseudomonas populations in the rhizosphere of seedlings grown in cultivated cores were reduced by 50% compared with the DD treatment, while sterilisation reduced populations by 65%. An assessment of the inhibitory activity of pseudomonads towards wheat seedlings in a test-tube bioassay indicated that reduced growth in DD cores was more closely related to the deleterious activity of Pseudomonas spp. toward root growth than to their population in the rhizosphere. A close relationship existed between the inhibitory activity of Pseudomonas spp. and the response of wheat seedlings to both cultivation (r = 0.859) and sterilisation (r mp;equals; 0.842).
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