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A greenhouse study was conducted to investigate the uptake of Cd, Ni, Pb, Co, and Zn by fodder rape (Brassica napus L. ‘Kenton’) and extractability of these metals from sewage sludge‐treated soils at different levels of sludge application and soil pH. Metals extracted by several extractants were correlated to their uptake by rape. Total uptake of Cd, Ni, Pb, and Zn increased and that of Co decreased as the rate of sludge application increased. Uptake of all metals except Pb generally decreased as soil pH increased.The extractability of most metals was in the order: HNO3 > aqua regia > HCl > NH4OAc (pH 4.8) > DTPA > H2O. It was governed by rates of sludge application but was little affected by change in soil pH. The percentage of exchangeable form of all metals was < 1% and 90 to 99% of the total metals in sludge‐treated soils was bound in organic and sulfide forms.Cadmium extracted by HCl, NH4OAc (pH 4.8), and diethylenetriaminepentaacetic acid (DTPA) as well as that determined after digestion of soil with HNO3 and aqua regia showed significant correlation with its uptake by rape. The same was true for Pb except for HNO3, where correlation coefficient was not significant. For Co, Ni, and Zn, none of the extractants used gave an adequate prediction of their plant availability, as most of the correlation coefficient values obtained were low. Of the extractants used in this study, though none gave a reliable prediction of plant availability of all the metals, DTPA yielded significant r values for Cd and Pb. Thus, DTPA may be considered better than other extractants for predicting the availability of Cd, Pb, and possibly Zn in fodder rape under varying levels of sludge application and soil pH.

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In a long-term experiment conducted (1967 -2001) at Hisar, India, pearl millet (Pennisetum typhoides) and wheat (Triticum aestivum) was grown during summer and winter in a rotation. The treatments consisted of farmyard manure (FYM) at the rate of 15, 30 and 45 Mg ha 7 1 during one or both the seasons. A treatment without FYM was maintained as a control. This made the total number of treatments 10, along with 2 levels of nitrogen at 0 and 120 kg ha 7 1 . Samples from 0 -15, 15 -30 and 30 -45 cm soil depths were collected and analysed for DTPA extractable and total content of zinc, iron, manganese and copper. Application of FYM significantly increased the DTPA extractable and total content of all the studied micronutrients in all soil depths. The increase was higher in the surface layer than in the lower depths. The time of application of FYM influenced the content of soil micronutrients. DTPA extractable and total content of micronutrients was higher when FYM was applied in winter as compared to summer. Application of N has no effect on DTPA extractable or total micronutrients content.

The availability of N, P, K, and organic-C content of soil at 0-to 15-, 15-to 30-, and 30-to 45-cm depths were estimated in a long-term field experiment testing farmyard manure and fertilizer-N doses in a pearl millet-wheat cropping sequence. Application of farmyard manure increased available P, K, and organic-C content of soil at all depths and doses of fertilizer-N. Available N content decreased from its original content (100 mg N kg -1 ) with the application of farmyard manure as well as fertilizer-N due to cropping of pearl millet and wheat crops during the last 20 years. Application of increasing doses of fertilizer-N had very little effect on available P, K, and organic-C content of soil; however, available N increased significantly (p = 0.05). Available P, K, and organic-C content of soil can be maintained to their original contents with the application of 8.2, 2.4, and 7.5 Mg farmyard manure ha -1 year -1 , respectively, along with 120 kg N ha -1 .