Surface soil samples from a wide range of naturally occurring soils were obtained for the purpose of studying the characteristic variations in soil reflectance as these variations relate to other soil properties and soil classification. A total of 485 soil samples from the U.S. and Brazil representing 30 suborders of the 10 orders of Soil Taxonomy was examined. Spectral bidirectional reflectance factor was measured on uniformly moist soils over the 0.52 to 2.32 µm wavelength range with a spectroradiometer adapted for indoor use.Five distinct soil spectral reflectance curve forms were identified according to curve shape, the presence or absence of absorption bands, and the predominance of soil organic matter and iron oxide composition. These curve forms were further characterized according to genetically homogeneous soil properties in a manner similar to the subdivisions at the suborder level of Soil Taxonomy. Results indicate that spectroradiometric measurements of soil spectral bidirectional reflectance factor can be used to characterize soil reflectance in terms that are meaningful to soil classification, genesis, and survey.
Recent breakthroughs in remote‐sensing technology have led to the development of high spectral resolution imaging sensors for observation of earth surface features. This research was conducted to evaluate the effects of organic matter content and composition on narrow‐band soil reflectance across the visible and reflective infrared spectral ranges. Organic matter from four Indiana agricultural soils, ranging in organic C content from 0.99 to 1.72%, was extracted, fractionated, and purified. Six components of each soil were isolated and prepared for spectral analysis. Reflectance was measured in 210 narrow (10‐nm) bands in the 400‐ to 2500‐nm wavelength range. Statistical analysis of reflectance values indicated the potential of high dimensional reflectance data in specific visible, near‐infrared, and middle‐infrared bands to provide information about soil organic C content, but not organic matter composition. Although reflectance in the visible bands (425–695 nm) had the highest correlation (r = −0.991 or better) with organic C content among the soils having the same parent material, these bands also responded significantly to Fe‐ and Mn‐oxide content. For soils formed on different parent materials, five long, middle‐infrared bands (1955–1965, 2215, 2265, 2285–2295, and 2315–2495 nm) gave the best correlation (r = −0.964 or better) with organic C content. Several wavebands were identified in which the soils were separable, but the reflectance response was dominated by soil factors other than organic matter content, indicating that choice of wavebands should not be based on spectral curve separability alone.
Soil and water losses from plots representing field areas between rills were studied for four rates of straw mulch at four slope steepnesses. Three simulated rainstorms totaling 2 hours at 6.4 cm/hour were applied to a 61‐ by 61‐cm test area of Russell silt loam soil.Interrill erosion was reduced about 40% by mulch applied at a rate of only 0.5 metric tons/ha and about 80% by 2 tons/ha, as compared with no mulch. Erosion was negligible at the 8 tons/ha rate. Soil losses from the interrill areas at 20% slope were only about double those measured at 2% slope, whereas widely used erosion equations show that total field erosion would increase about 20‐fold over this range of steepnesses.Water loss by runoff was independent of slope steepness, but it was slightly reduced by mulch at a rate of 2 tons/ha and was greatly reduced by the 8 tons/ha rate. After 40 minutes of rainfall, sealing of the soil surface by raindrop impact had reduced infiltration rates for treatments with 0 to 2 tons/ha of mulch to only 20% of those with 8 tons/ha.
Reflectance, transmittance and absorptance spectral of "normal" and six types of nutrient-deficient (N, P, K, S, Mg, and Ca) maize (Zea mays L.) leaves were analyzed at 30 selected wavelengths from 500~2600 nm. The analysis of variance showed significant differences in reflectance, transmittance and absorptance in the visible wavelengths among leaf numbers 3, 4, and 5, among the seven treatments, and among the interactions of leaf number and treatments. In the infrared wavelengths only treatments produced significant differences.The chlorophyll content of leaves was reduced in all nutrientdeficient treatment s. Percent moisture 'was increased in S-, Mg-, and N-deficiencies. Positive correlations were obtained (r = 0.7) between moisture content and percent absorption at both 1450 and 1930 nm. Polynomial regression analysis of leaf thickness and leaf moisture content showed that these two variables were significantly and directly related (R = 0.894). Leaves from the P-and Ca-deficient plants absorbed less energy in the near infrared than the normal plants; S-, Mg-, K-, and N-deficient leaves absorbed more than the normal.Leaf thermo grams were prepared on normal and S-and Ndeficient leaves. Both S-and N-deficient leaves had higher temperatures than normal maize leaves.
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