Rice growth under different stubble and nitrogen-fertilization management techniques

Abstract

The effects of stubble and N fertilization management techniques on crop growth were studied in a series of factorial experiments in fields which had up to five consecutive annual rice (Oryza sativa L.) crops. Incorporating rather than burning the previous crop's stubble 2 to 6 months before sowing the next crop had little effect on growth of the first three crops, but increased tillering and dry-matter (dm) accumulation by an average of 27% during the fourth and fifth crops. Growth on unfertilized plots fell by half between the first and second crops, and it was necessary to apply 210 kg N ha−1 to the fourth and fifth crops to obtain similar dm production to that resulting from applying 50 kg N ha−1 to the first crop. Time of N application accounted for up to 64% of the variation in crop growth. Fertilization at sowing had little effect on growth, but plots fertilized just prior to permanent flood (PF) had up to double the dm of unfertilized plots. When N was applied at PF to the fourth and fifth crops, significant linear increases in growth occurred with each 70 kg N ha−1 increment to at least 210 kg N ha−1. Applying up to 140 kg N ha−1 at panicle initiation (PI) also increased crop growth, but the increase was less than that obtained when N was applied at PF. Heavy N application at PI produced many sterile late-tillers. Rice crops with 700–850 shoots m−2 and 3–4 t dm ha−1 just prior to PI gave highest grain-yield. This growth was achieved under continuous annual rice-cropping when large quantities of N were applied at PF. A management package of stubble incorporation in each autumn-winter period, plus increased N application at PF, is recommended.