Effect of nitrogen application through urea and Azolla on yield, nutrient uptake of rice and soil acidity indices in acidic soil of Meghalaya

ABSTRACT

Aim: To investigate the effect of nitrogen application through urea and Azolla on yield, nutrient uptake of rice (Oryza sativa L.) cv. Shasharang and to assess the improvement in soil acidity indices in acidic soil of Meghalaya.Methodology: A field experiment was conducted with six treatments viz., control (T1), Azolla incorporation @ 1.6 tonnes ha-1 (T2), 30 kg N ha-1 through urea (T3), 60 kg N ha-1 through urea (T4), 30 kg N ha-1 through urea + Azolla incorporation @ 1.6 tonnes ha-1 (T5) and 60 kg N ha-1 through urea with Azolla incorporation @ 1.6 tonnes ha-1 (T6). The experiment was laid out in RBD and replicated four times. The physico-chemical properties of the experimental soil were pH 5.1, SOC 1.75 percent, available N, P and K as 288.62, 17.23 and 201.46 kg ha-1, respectively. Results: The application of 60 kg N ha-1 through urea along with Azolla incorporation @ 1.6 tonnes ha-1 (T6) recorded highest dry matter i.e. 58. 15 g hill-1 at maturity of rice. Similarly, 60 kg N ha-1 through urea with Azolla incorporation @ 1.6 tonnes ha-1 produced highest grain and straw yield i.e. 4.2 t ha-1 and 7.68 t ha-1 followed by T5 and T4. The magnitude of increase in N, P and K concentration and uptake in grain was 28.57, 97.02; 26.09, 84.21 and 15.69, 76.47 percent in T6 over T1. The analysis of soil acidity indices indicated that highest improvement in pH was observed in T2 over all other treatments. Further, pH increased significantly in the treatments receiving Azolla incorporation (T2, T5 and T6) compared with the sole application of urea/control (T1, T3 and T4). The exchangeable calcium and magnesium (meq 100 g-1), CEC (meq 100 g-1) and base saturation percentage also showed the same trends and the highest values were observed as 1.92, 7.90 and 24.30 in T2. However, in contrast to this, the lowest values of exchangeable aluminium, exchangeable acidity and acidity saturation percentage were observed in T2 indicating that the sole application of Azolla improved soil acidity indices. Interpretation: It may be concluded from the present study that Azolla-urea nitrogen system may be suitable for getting optimum production of rice under tropical conditions and improving soil acidity indices because of its ability to fix atmospheric nitrogen.