Responses of cotton growth, yield, and biomass to nitrogen split application ratio

Abstract

The conventional nitrogen (N) rate is 300 kg/ha in cotton production in the field with middle level fertility in the Yangtze River Valley in China. Applications of N are usually split into a pre-plant application (PPA), a first bloom application (FBA), and a peak bloom application (PBA), at percentages of 30%, 40%, and 30%, respectively. However, the facts of little positive yield response with a higher N rate, water nutrition enrichment, and cotton early senescence are universal. The purposes of this study were to understand and determine the cotton yield using a lower N rate but allocating more N to the late growing period (PBA) and to specify the characteristics of cotton growth and biomass accumulation by the alteration. Fixing the N rate at 225 kg/ha and FBA ratio at 40%, the effects of different balances for the remaining 60% N between PPA and PBA on cotton ( G. hirsutum L. var. Huazamian H318) growth, yield, and biomass were studied in field trials (2008 and 2009) and a pot trial (2009). The results showed that the balance of 0% PPA and 60% PBA ratio had a shorter seedling period and a longer flowering and boll setting period, compared to the balance of a higher PPA and lower PBA ratio. Both field and pot trials showed the same trend but significant differences existed among treatments in the pot trial. Cotton lint yield was as high as 1200 kg/ha for PA treatment (0% PPA + 60% PBA), which was significantly higher than any other treatments since it had a higher biomass accumulation speed in both the average (1.3 g/d) and the highest (4.51 g/d) during the fast biomass accumulation period, a higher total biomass (189.7 g/plant) and a higher harvest index (16.82%). These results suggest that allocating more N to PBA should increase cotton biomass, harvest index, and yield.