N fertilizers and high yielding varieties were major drivers of the enormous increase in rice productivity during the past 50 years. Despite increasing food production higher nitrogen use also contributed in environmental pollution and Increasing consciousness of conservation of environment and mitigation of climate change brought a major shift in cultivation practices of major crops towards organic agriculture. An important issue regarding the acceptance of organic agriculture is the question of productivity. In addition to readily available ammonium and nitrate ions, the soil of organic agriculture can contain a wide range of organic nitrogen compounds such as peptides, proteins, free amino acids, amino sugars and nitrogen heterocyclic compounds. The root system architecture (RSA) features are of utmost importance for increasing nitrogen use efficiency of future climate-resilient varieties. From a fundamental point of view, the influence of nitrogen on root development is still poorly understood. Modulating root architecture is a strategy that aims at developing crops that capture nutrients more efficiently and are thus suitable for sustainable agriculture with fewer fertilizer inputs. Our experiment aimed to study the responses of IR-28 root system architecture to the availability of different forms of nitrogen, including organic at seedling stage, so that we can understand up to what extent our current rice varieties, which are exclusively breed for intensive agriculture, are suitable for organic agriculture. From the experimental results it was indicated that root parameters viz. seminal root length was significantly reduced due to the availability of nitrogen in nitrate and ammonia while increased with organic N. Main root angle was significantly increased with increasing N concentration and it became more steeper under the deficiency of N. Straightness of main root does not affected by the availability of N while the sources of nitrogen had significant effect and maximum straightness observed in organic N treated plant while minimum in ammonium treated. Lateral root number was increased with increasing nitrogen as nitrate and ammonia up to 100% as compared to organic N. Mean lateral root length was significantly affected by the sufficiency of nitrogen, while does not fluctuate with various forms of nitrogen. Sum of lateral root length was higher in nitrogen sufficiency. Lateral root density was significantly responding to availability and non-availability of nitrogen and significant reduction was observed in 0% N condition. Total root system size significantly influenced by sources and levels of nitrogen. Moreover, amongst root traits, total root system size was found least phenotypic plastic while lateral root density was ranked as highest phenotypic plastic trait due to nitrogen. The results indicate that combined nitrogen nutrition through nitrate and ammonia is most suitable for root system and seedling growth of rice as compared to the sole sources. The results of these study support the view that we need to breed varieties suited for organic agriculture and varieties such as IR-28, which is select and breed for high nitrogen input intensive agriculture, may not be efficient for organic nitrogen uptake and/or assimilation.

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