Extraction of Subsoil Nitrogen by Alfalfa, Alfalfa–Wheat, and Perennial Grass Systems

Abstract

The role of alfalfa (Medicago sativa L.) in extracting NO3–N from deep soils of areas with cold, short growing seasons, such as western Canada, is not well understood. A study was established in 1990 to determine NO3–N extraction ability to 300 cm; initial soil NO3–N concentrations were high (>8 mg kg−1). Systems included continuous alfalfa; annual rotations of spring wheat (Triticum aestivum L.), field pea (Pisum sativum L.), and barley (Hordeum vulgare L.); a native‐grass system [big bluestem (Andropogon gerardi Vitman) and western wheatgrass (Agropyron smithii Rydb.)]; and continuous fallow. The annual rotation effectively lowered NO3–N to <2.3 mg kg−1 in the 30‐ to 90‐cm depth. By the 4th yr, alfalfa had reduced NO3–N concentrations to <3.8 mg kg−1 for the 30‐ to 240‐cm increment. The greatest NO3–N extraction benefits of alfalfa were realized in the 4th yr at a maximum soil depth of 270 cm. Subsoil NO3–N concentration increased in the continuous alfalfa between the 4th and 6th yr. Greater NO3–N extraction occurred with the native‐grass treatment compared with continuous alfalfa in the 0‐ to 120‐cm soil depth; however, similar extraction patterns existed below 120 cm. A system involving 4 yr of alfalfa followed by two wheat crops resulted in the lowest subsoil NO3–N concentration, even lower than the continuous alfalfa and native‐grass systems. It was concluded that subsoil NO3–N extraction with alfalfa was maximized when alfalfa was rotated with annual crops.

Effects of input level and crop diversity on soil nitrate-N, extractable P, aggregation, organic C and N, and nutrient balance in the Canadian Prairie

“…Compared with annual crops which extracted nitrate-N only from 0-120 cm soil depth, alfalfa extracted significant amounts of nitrate-N to 270 cm soil depth (Entz et al 2001). Peterson and Russelle (1991) reported that alfalfa can absorb nutrients from depths of 11 m. However, Campbell et al (1994) and Voorhees and Holt (1969) stated that the depth of significant nutrient extraction by alfalfa was approximately 2.5 m. Nutrients present in the sub-soil may thus be used by taproot plants and become available in surface soil after crop residues are returned to the soil.…”

Accumulation of nitrate N in the soil profile and its implications for the environment under dryland agriculture in northern China: A review

“…These findings suggest that frequent summer fallow can cause large accumulation of NO 3 -N in soil and occasional heavy rains in relatively dry regions can result in downward movement of NO 3 -N deep into the soil profile. To minimize NO 3 -N leaching problem, it is suggested that producers should reduce or even eliminate summer fallow (especially tilled) by increasing cropping frequency using no-tillage (Campbell et al 1984;Guillard et al 1995;Zentner et al 2001), proper crop rotations to include perennial grasses with deep/ extensive rooting system and high N requirements (Olsen et al 1970;Entz et al 2001) or cover crops (Vos et al 1998). However, quantitative information is needed on the actual contribution of increased cropping frequency using no-tillage and inclusion of deep-rooted perennial and annual crops in rotations in minimizing NO 3 -N accumulation and leaching in the soil profiles.…”

Effects of resting perennial pastures during the sensitive pre-dormancy period in western Manitoba: Pasture productivity and beef cattle performance

“…to more shallow-rooted grass species (Entz et al 2001). It also has a higher optimum temperature for growth than cool-season grasses.…”

“…As perennial pastures begin using soil moisture as soon as green-up occurs in the spring (Twerdoff et al 1999), they frequently have utilized almost all-available soil moisture by late summer (Twerdoff et al 1999;Bradshaw 2007). In addition to the decreasing soil water, air temperatures in the southern prairies during the JulyÁ August period can exceed 308C, which exacerbates slow growth resulting in early dormancy of cool-season grasses (Frank et al 1996;Baron and Belanger 2007).…”