|Black, Alfred - RETIRED; USDA-ARS-NGPRL|
Submitted to: Proceedings Sunflower Research Workshop
Publication Type: Proceedings
Publication Acceptance Date: March 10, 2000
Publication Date: N/A
Interpretive Summary: Sunflower is the major oilseed crop in the United States portion of the Northern Great Plains region. Agronomists have shown that sunflower can extract water and soil nitrogen from deeper in the soil than can small grain crops. We wanted to directly observe the root growth patterns of sunflower to better understand such agronomic findings. Two methods were used to observe root growth: one, by using a miniature video camera to magnify images of roots growing up against walls of plastic tubes (known as minirhizotrons) installed in the field, and second, by directly observing root growth in trenches. The maximum sunflower root growth depth observed with minirhizotrons in our soil was 5.9 feet, while we observed a maximum depth of 5.7 feet using a trench. In a continuous crop rotation, minirhizotron measurements showed that sunflower rooting was deeper in a no-till treatment compared to minimal-till (with undercutter) and conventional-till (with disking). In another experiment with eight crops species, sunflower rooted more deeply than legume crops (dry bean, pea, soybean), mustards (canola, crambe), and spring wheat, with only safflower being more deeply rooted.
Technical Abstract: Sunflower root growth patterns were measured using minirhizotron-microvideo methodology in two field experiments. The trench profile technique was also used to directly observe root growth of sunflower. Maximum rooting depth observed by minirhizotrons was 5.9 feet (1.8 m) compared to a maximum of 5.7 feet (1.7 m) observed directly by trench profile technique. Fallow and no-till treatments resulted in a greater average depth of root growth in sunflower compared to minimal-till and conventional-till treatments. Maximum root growth depths observed in the same experiment in 1992 and 1993 were also greatest in fallow and no-till treatments. Total root length growth of sunflower observed in 1992 and 1993 reached a peak value and then declined. Greatest total root length growth in 1992, a year with average precipitation, was about 200 cm/cm2 (10 mile/yard2) compared to approximately 100 cm/cm2 (5 mile/yard2) in 1993, a year with far greater than average precipitation. In a 3-year comparison of 8 crops including 3 annual legumes, 2 mustard family crops, and spring wheat, median and maximum root growth depths of sunflower were exceeded only by that of the safflower crop.