|Goins, Gregory - FORMER ARS EMPLOYEE|
Submitted to: Proceedings Of The Minirhizotron Workshop
Publication Type: Abstract Only
Publication Acceptance Date: September 1, 1995
Publication Date: N/A
Technical Abstract: In perennial forages like alfalfa, repeated herbage removal may alter root production and mortality, and thereby affect nutrient uptake and loss. Our objective was to determine the extent and patterns of fine-diameter root production and loss during alfalfa establishment. An experiment was conducted in a loamy sand soil in Minnesota, USA, using horizontally installed minirhizotrons placed directly under the seeded rows at 10, 20 and 40 cm depths. Four alfalfa germplasms (Agate; Ineffective Agate, a non-N2-fixing near isoline of Agate; a germplasm with few fibrous roots and strong taprooted traits; and a germplasm with many fibrous roots and a strongly branched root architecture) were seeded in four replicate blocks in early June 1994. Images collected biweekly throughout the initial growing season were processed using CMAP-Roots software. More than 50% of all fine roots in the upper 20 cm were produced in the first 7 wk of growth. Root production was similar among germplasms, except that the fibrous rooted selection produced 29% more roots at 20 cm. About 10% of roots at 10 cm developed into secondarily thickened roots, and about one half of these were roots produced in the first 3 wk. By the end of the growing season, greatest fine root loss (49%) had occurred in the uppermost depth and least at 40 cm (ca. 33%), but contemporaneous root cohort survival was not related to soil depth in a simple fashion. There was a pronounced disappearance of fine roots in the 2 wk following herbage removal. Fine roots produced during this time also tended to have the shortest median life spans. These data indicate that plant germplasm and management have significant influences on alfalfa fine root demography during stand establishment.