Studies on the measurement and behaviour of nitrogen in soil

• Main Author: Amin, Mohammad
• Published: University of Glasgow 1995
• Subjects: 631.4; QD Chemistry
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.633822

This study of the measurement and behaviour of nitrogen in soil is split into three main parts: 1) An investigation of the Kjeldahl digestion method for measuring total nitrogen in soil and plant materials. 2) A study of the effect of air drying, temperature and repeated ammonium application on nitrification rates and 3) An investigation of ammonium contamination at a former nylon factory site. The investigation of the Kjeldahl digestion method was made by comparing measured values of total nitrogen using a standard Kjeldahl digestion method and salicylic acid modification digestion method. For each method three different catalyst mixtures were used. Measurements were made of certified reference plant materials (hay and cabbage) and a comparison was made of two soil samples. The standard Kjeldahl digestion method with 1 g of sodium sulphate/copper sulphate mixture (100:10) measured significantly lower nitrogen (P<5%) than the certified reference value for hay but not cabbage. Significantly lower (P<5%) total nitrogen was measured in soil samples than with 2.5 g of sodium sulphate/copper sulphate mixture (110:10) and Kjeltabs (2.5 g potassium sulphate/copper sulphate/selenium, 100:10:1). The reason for the lower recovery of total nitrogen with 1 g of catalyst is the lower digestion temperature which causes incomplete digestion. The 2.5 g of catalyst mixture and Kjeltabs with the standard method gave significantly (P<5%) higher total nitrogen than the certified values for both hay and cabbage. The high values of total nitrogen measured for plant material were probably due to variable recovery of the high levels of nitrate which were present in the plant material at 3.1 mg g -1 (hay) and 3.2 mg g-1 (cabbage).The salicylic acid modification method measured significantly higher total nitrogen than the certified reference values using all catalyst mixtures with both plant materials. This higher recovery of total nitrogen was due to partial recovery of nitrate as the method used for the certified values would not have recovered nitrate.