Evaluation of Nutrient Contribution by Sunn Hemp at Different Growth Stages in Paddy Soil

Abstract

Green manuring contributes to nitrogen availability through biomass decomposition and also increases the soil carbon sequestration. The study aimed to estimate biomass contribution of sunn hemp at various growth stages and the mineralization of sunn hemp after incorporation into paddy soil under submerged condition, focusing on synchronizing nitrogen supply with rice crop demand. Sunn hemp was harvested at different growth stages (45, 60 and 75 days after sowing) to assess its biomass and nutrient contributions, particularly nitrogen and carbon. The harvested plants were incorporated into the soil, and rice seedlings were transplanted a week later. Nitrogen mineralization was monitored over eight weeks, alongside rice plant nitrogen uptake. The study was conducted at the Department of Agricultural Research, Nay Pyi Taw, with four treatments: control (no sunn hemp), SH45 (45 DAS), SH60 (60 DAS), and SH75 (75 DAS). Analytical results of sunn hemp at different growth stages showed minimal variation, however significant differences were observed in fresh and dry biomass weight. SH75 and SH60 contributed fresh biomass together with nitrogen and carbon three times higher than that of SH45. Nitrogen mineralization from different ages of sunn hemp reached maximum within first two weeks. Considering mineralization percentages, SH60 and SH75 showed continuous mineralization from 1st to 8th week, however mineralization in SH45 declined and approached to zero from 5th to the 8th week. Nitrogen demand of rice plants started at 3rd week of SH incorporation into the soil, reached maximum at 6th week and continued to 8th week. Synchronization between nitrogen supply and demand was observed from the 3rd to the 8th week with the incorporation of SH60 and SH75, whereas in the  case of SH45, it was limited to the period between the 3rd and 5th week. The research highlighted the nutrient provision potential of sunn hemp at different ages to rice plant under submerged paddy soil.