Agricultural soils can act as a potential sink of the increased carbon dioxide in the atmosphere if managed properly by application of organic manures and balanced fertilizers. However, the rate of carbon (C) sequestration in soils is low in warm climates and thus the short term changes in soil organic carbon (SOC) contents are almost negligible. Therefore, the knowledge about other C fractions that are more sensitive or responsive and indicative of the early changes in SOC can help to determine the effect of the management practices on soil C sequestration. The objective of this study was to determine the soil C sequestration after 16-years of applications of chemical fertilizers and farmyard manure (FYM) to rice (Oryza sativa)-cowpea (Vigna unguiculata) rotation system in a sandy loam soil (Typic Rhodalfs). The treatments were-(1) one control (no fertilizer or FYM); (2) three chemical fertilizer treatments [100 kg N ha -1 (N), 100 kg N ha -1 ? 50 kg P 2 O 5 ha -1 (NP), 100 kg N ha -1 ? 50 kg P 2 O 5 ha -1 ? 50 kg K 2 O ha -1 (NPK)]; (3) one integrated treatment [(50 kg N ha -1 ? 25 kg P 2 O 5 ha -1 ? 25 K 2 O ha -1 ) ? (50 kg N ha -1 from FYM)]; and (4) one organic treatment at10 Mg ha -1 FYM. Compared to the control treatment, the increase in SOC was 36, 33, and 19% greater in organic, integrated, and NPK treatments. The 16-years application of fertilizers and/or FYM resulted in much greater changes in water soluble C (WSC), microbial biomass C (MBC), light fraction of C (LFC), and particulate organic matter (POM) than SOC. Of the SOC, the proportion of POM was highest (24-35%), which was followed by LFC (12-14%), MBC (4.6-6.6%), and WSC (0.6-0.8%). The application of fertilizers and/or FYM increased the mean weight diameter of soil aggregates; thus provided physical protection to SOC from decomposition. Our results suggests that the application of fertilizers and/or FYM helps to sequester C in the soil and that the labile fractions of C can be used as indicators to determine the amount of C sequestered as a result of different management practices.

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In the present study, Arsenic (As) concentrations in underground water, soil, and plants (rice) and their inter-relationships in central and sub-mountainous Punjab, India were studied. Approximately, 32% of the tubewell water samples had As concentrations greater than the maximum permissible limit (10 μg As L(-1)) set by the World Health Organization (WHO) whereas in hand pump waters, As concentrations were within the safe range (i.e. <10 μg As L(-1)). As concentrations in tubewell waters were significantly correlated with As concentrations in surface soil (r = 0.57; P < 0.05) and plant samples (r = 0.27-0.82; P < 0.05) in central and sub-mountainous Punjab. The estimated daily intake of As through human consumption in rural and urban population was 0.016 and 0.012 μg day(-1) kg(-1) body weight respectively.

Ground-based radiometric measurements in the red and infrared bands were used to monitor the growth and development of wheat under irrigated and stressed conditions throughout the 1987-88 and 1988-89 growth cycles. Spectral data were correlated with plant height, leaf area index, total fresh and total dry biomass, plant water content and grain yield. The radiance ratio (R) and normalized difference vegetation index (NDVI) were highly and linearly correlated with yield, establishing the potential which remote sensing has for predicting grain yield. The correlation for R and NDVI was at a maximum between 75 and 104 days after sowing, corresponding with maximum green crop canopy cover. The differences in spectral response over time between irrigated and unirrigated crops allowed detection of water stress effects on the crop, indicating that a hand-held radiometer can be used to collect spectral data which can supply information on wheat growth and development.Efectos de lafalta de agua en el trigo RESUMEN Se utilizaron mediciones radiometricas del suelo en las banda roja e infrarroja para monitorizar el crecimiento y desarrollo de trigo bajo condiciones de irrigation y de escasez de agua durante todo el transcurso de los ciclos de crecimiento de 1987-88 y 1988-89. Los datos espectrales fueron correlacionados con la altura de planta, indice de superficie de hoja, total de biomasa fresca y seca, contenido de agua en la planta, y rendimiento de grano. La intensidad de radiation (R) y el indice de vegetation con diferencia normalizada (IVDN) fueron correlacionados en forma lineal y elevada con el rendimiento, estableciendo el potencial de la detection remota para predecir el rendimiento de grano. La correlation de R y IVDN estuvo en un maximo de entre 75 y 104 di'as a partir de la siembra, correspondiendose con el maximo de cobertura verde de la cosecha. Las diferencias en la respuesta espectral de las zonas irrigadas y las no irrigadas con el paso del tiempo permitio detectar los efectos de la falta de agua en la cosecha, lo cual senalo que se puede utilizar un radiometro de mano para recolectar datos espectrales que pueden suministrar information relacionada con el crecimiento y desarrollo del trigo.

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