Physiological determinants of high yielding ultra-narrow row cotton: Biomass accumulation and partitioning

Ultra-narrow row (UNR) cotton, may have the potential for increased yields in high yielding, high-input production systems. Attaining higher yields in UNR cotton relative to conventionally spaced crops must depend on either increased biomass production or partitioning to fruit. We compared biomass production and partitioning in UNR treatments (25 cm spaced rows) to that of treatments with conventionally spaced rows (100 cm) in high yielding, high-input production systems (where lint yield was greater than 1800 kg ha−1). Early biomass accumulation was faster in the UNR crop (36 plants m−2) compared to the conventionally spaced treatments (12 plants m−2) but slowed later in the season. Despite a three fold increase in plant density in the UNR treatments total dry matter production per unit area was not different to the conventionally spaced treatments. On a per plant basis dry matter accumulation was slower and total biomass production was significantly lower in the UNR crops. This was accompanied by a decrease in boll size, suggesting that competition for resources was limiting crop growth. These differences were significant across three seasons. However, the increase in yield in the UNR crops was obtained through increased partitioning of dry matter to fruit compared to the conventionally spaced crops, resulting in higher boll numbers and increased lint yield in high-input UNR production systems. As there were no differences between row spacings in total water use or nitrogen uptake, investigations are continuing to determining the key determinants limiting crop growth and biomass production in high-input UNR production systems.

► We compared biomass production and partitioning to fruit in UNR cotton to 100 cm rows over three seasons.
► UNR crops accumulated biomass faster initially but final biomass production was the same as the conventionally spaced crop.
► Increased partitioning to fruit in the UNR crop led to increased lint yield.
► Decreased boll size and slower crop growth rate per plant indicated that competition was limiting plant growth in high-input UNR cotton.