Effect of urea and manure addition on changes in mineral-N content in soil profile at various growth stages of wheat

Distribution of mineral-N in the soil profile at four growth stages of wheat (35, 70 and 105 days after sowing and at maturity) as influenced by application of nitrogen through urea, farmyard manure and biogas slurry in a rice-wheat sequence was studied. The effects of N application were studied in three phases of manuring – cumulative (manuring both rice and wheat), residual (manuring rice only) and direct (manuring wheat only). Nitrate (NO₃)–N contents in different soil layers was more than that of NH₄-N at each growth stage of wheat. Total mineral-N content at different depths was influenced by the total quantity of N applied to the rice-wheat system, irrespective of the source. Contents of both NO₃ and NH₄-N at all the soil depths in each of the three manuring phases showed a declining trend with growth of wheat. Computation of total mineral-N forms in the soil profile up to 180 cm under different treatments at various stages of wheat growth indicated wide variation in their accumulation in each of the three manuring phases. The amount of N applied through urea and manures had a direct bearing on accumulation of NO₃ and NH₄-N in the 0–180 cm soil depth. Peak NO₃-N concentration occurred at 45–60, 30–45 and 15–30 cm soil depths in the plots receiving N through urea alone, urea + farmyard manure and urea + biogas slurry, irrespective of manuring phases. On the other hand, peak NH₄-N concentrations were noticed at 30–45 cm soil depth, in all the manuring phases irrespective of the level and source of applied N. Farmyard manure resulted in more accumulation of mineral-N in the soil profile than biogas slurry.