Soybean root growth and soil water extraction at different row spacings.

BREVEDAN, R.E.; MIRASSÓN, H.; FIORETTI, M.N.; BAIONI, S.S.

Beijing, China

Conferencia; First International Conference on the Theory and Practices in Biological Water Saving.; 2006

The evaluation of the potential production and the management practices (row spacing, plant population, etc.) needed to optimize soybean yield in the subhumid and semiarid region of the pampean provinces of Argentina, are very important due to the diffusion of the crop in the region. Root growth is essential to determine the growth and yield of soybean in water-limited environments. Many droughted crops leave a substantial amount of available water in the subsoil, suggesting that root characteristics may be limiting water extraction. Little is known about the growth of crop root system in relation to soil water extraction. Research was conducted to modify crop management in order to allow a deeper or a more complete soil water extraction. During two years the effects of different row spacings on rooting density and water extraction was evaluated. Spacings between rows of 0.18; 0.35 and 0.70 m were compared at equivalent plant density. The objective of this report was to evaluate the changes in the rooting pattern, water use and yield of soybean under different row spacings in the subhumid pampean region of Argentina. Field experiments were conducted at Tres Picos (Buenos Aires province, 38°16’S 62°13’W) during two years to measure the effects of row spacings on water use and seed yield. Experiment was conducted in a sandy loam. The experiment was set in a randomized complete block design with 3 row spacings (0.18; 0.35 and 0.70 m) and 6 replications. Plant population was 350,000 pl ha-1. Each plot consisted of 6 rows. Soybean (cv A3205) was seeded on November 15. Three sets of root and shoot samples were taken at R1, R3 and R5 stage. Roots were separated from soil washing with water. Then were separated from organic debris and stored in an ethanol-water solution until were made length measurements. Root length was estimated according to Newman’s line intercept method modified by Tennant (1975) (J. Ecol. 63:995-997). Soil moisture was determined by a neutron probe (Troxler model 1255 with scalimeter model 2600). Readings were taken weekly in 0.25 m increments up to 1.50 m. The crop received a post sowing irrigation (70 mm) at 8 days after sowing, which were equal and common to all plots, to establish the crop stand. Soybean grown in narrower rows had greater root length density in most of the soil layers but roots in the wider row grow deeper. Anyway, most roots were located in the upper 0.25 m of the soil profile. Yields of 0.18 and 0.35 m rows were significantly higher than with 0.70 m in both years. The difference was due to a higher number of seeds. There was no effect of row spacing on seed size. Soil water content was usually highest for the 0.70 m row spacing. The difference with narrower rows tended to decrease as the season progressed. Soil water depletion was generally confined to the upper 1 m of the soil profile. Increased soybean yield by planting in narrow rows is probably due to a more extensive root system that can make a more thorough use of the water stored in the soil. During the late reproductive stages usually will rain in the region and this compensate the early use of water by soybean grown in narrow rows, that otherwise can reduce yield.