Weed seed bank diversity and community shift in a four-decade-old fertilization experiment in rice-rice system

The development of management practices that allow the prediction of timing and extent of weed emergence is essential for planning more effective weed control strategies as well as maintenance of biodiversity in agricultural systems. A better understanding of the seed bank could provide useful insights into the long-term effects of organic and chemical fertilization for maintaining diversity. The effects of organic and inorganic fertilization on weed seed bank composition, density and diversity were studied in the soil of a long-term fertilizer experiment established four decades ago in CRRI, Cuttack, India. Weed seed density was lowest for Paspalidium flavidum (22 individuals per m(2)) and highest for Amniania baccifera (11,616 individuals per m(2)) irrespective of the treatments. Highest weed seed density was observed in farm yard manure (FYM) treatment whereas, lowest was in NK treatment, which was 232% higher in FYM over NK treatment. Weed seedling emergence was higher in kharif flushes and lowest in rabi. Principal component analysis ordination indicated little similarity in the weed community composition particularly among NP, NPK and NPK + FYM, while application of N alone was quite distant. Weed species diversity was reduced significantly with application of inorganic N either applied with K or alone; therefore, lowest diversity and species richness was observed in NK treatment followed by N alone. The results of the study may contribute to the development of effective weed management strategies as well as maintenance of weed diversity which leads to transition from an herbicide-dependent cropping system to a more environmentally friendly cropping system. (C) 2015 Elsevier B.V. All rights reserved.