Dynamics of Nitrogen Fractions with Long-term Addition of Lantana camara Biomass in Rice – Wheat Cropping Sequence

The long-term effect of Lantana camara biomass addition on different soil-N fractions in rice-wheat cropping was studied in an experiment which started from the wet season (July–Nov.) of 1988 with four levels of lantana (0, 10, 20 and 30 t ha⁻¹) on fresh weight basis and three levels of chemical N at Palampur, India. Lantana biomass was added only to rice to to 15 days before transplanting/puddling every year. The levels of N were 45, 67.5 and 90 kg ha⁻¹ to rice. The order of these three N levels was reversed for wheat to 120, 90 and 60 kg ha⁻¹ with the objective to find out the most suitable dose of chemical N in overall rice-wheat cropping sequence. At the end of six crop cycles viz. at the harvest of dry season (Nov.–May) wheat of 1993–94, with lantana addition from 10 to 30 t ha⁻¹, the highest build-up was observed in NO₃-N (55–70%) and lowest in NH₄-N (22–40%). Continuous incorporation of lantana @ to to 30 t ha⁻¹ increased all the hydrolysable N fractions significantly except unidentified-N which remained unaffected. Out of the total N added through lantana over the period of six years, maximum was transformed into amino acid (27.1–35.0%) followed by hydrolysable NH₄-N (25.6–32.9%) and a minimum into unidentified N (2.2–2.9%). Increased levels of N application also increased all the hydrolysable N fractions except unidentified-N. Amino acid-N, NH₄-N and hydrolysable NH₄-N were observed to be important N fractions contributing towards available N.