Yield responses to narrow rows as related to interception of radiation and water deficit in sunflower hybrids of varying cycle

Abstract

For sunflower, there are reports showing reduced distance between rows could be neutral, beneficial or counterproductive. In well-watered crops, yield response to distance between rows has been analysed in terms of fractional photosynthetically active radiation (PAR) interception during the most critical periods of grain set. The aim of this work was to advance our understanding of the interaction between row distance, water availability and cultivar type analysing yield responses in terms of capture of radiation. Five experiments were conducted in the southern Pampas of Argentina. The combination of seasons, sites, soil depth, sowing dates and cultivars generated a wide range of growing conditions, including contrasting water regimes. Crops in wide rows intercepted less radiation than their counterparts in narrow rows in all experiments, with significant differences in 6 of 14 cases ( P<0.05). Zenit, a short-season hybrid, consistently intercepted less radiation than its long-season counterparts ( P<0.01). Yield response to narrow rows was significant for Zenit in four out of five experiments, whereas long-season hybrids only increased yield in one experiment. For crops with low or moderate water deficit, yield did not respond to narrow rows when conditions were conducive to full interception in wide-row crops, but yield increased up to 15% when fractional PAR interception in wide-row crops was about 70%. For crops with severe water deficit, yield response ranged from 25% reduction when wide-row crops were close to full interception to 25% increase when fractional PAR interception was about 0.6. Increase in yield with narrow rows was largely related to increased grain number, whereas yield reductions were primarily related to reduced grain mass. Change in yield in response to row spacing was a linear function of change in fractional PAR interception; the rate of change in yield per unit change in fractional PAR interception fell from 1.3%/% in severely stressed crops to 0.24%/% in crops with low or moderate stress.