North American Agroforestry. Группа авторов

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rel="nofollow" href="#ulink_d6b9dffb-41c3-5804-9243-035e88c4e68e">Table 4–1. Effects of tree (poplar and maple) competition on photosynthetically active radiation (PAR) and crop (soybean and maize) yield at two distances from tree rows for two growing seasons (modified from Reynolds et al., 2007).

Parameter (N = 6) Crop Control Poplar Maple
2 m 6 m 2 m 6 m 2 m 6 m
1997 soybean
PAR, mmol s−1 m−2 1,464.0 a 1,586.0 a 1,133.0 a 1,370.0 a 1,045.0 b 1,558.0 a
Yield, t ha−1 2.51 a 2.59 a 1.04 b 1.97 a 1.29 b 2.00 a
1998 soybean
PAR, mmol s−1 m−2 1,405.0 a 1,158.0 a 746.0 b 1,296.0 a 670.0 b 1,336.0 a
Yield, t ha−1 2.24 a 2.25 a 1.15 b 1.67 a 1.55 b 2.85 a
1997 maize
PAR, mmol s−1 m−2 1,528.0 a 1,579.0 a 952.0 b* 1,407.0 a* 1,075.0 b* 1,525.0 a*
Yield, t ha−1 4.21 a 4.83 a 2.89 b 4.61 a 2.07 b 4.64 a
1998 maize
PAR, mmol s−1 m−2 1,422.0 a 1,200.0 a 794.0 b 1,117.0 a 481.0 b 1,420.0 a
Yield, t ha−1 5.70 a 5.88 a 0.69 b 5.29 a 3.79 b 7.07 a

      Note. Soybean and maize intercrops, July 1997 and July 1998. Within each treatment (control, poplar, maple), values in each row followed by the same letter are not significantly different (Tukey’s HSD, P < 0.05).

      * Significant at the 10% level.

      The physiological basis of yield reduction due to shading has been investigated by several studies in temperate agroforestry systems (Albaugh et al., 2014; Ehret, Graß, & Wachendorf, 2015; Miller & Pallardy, 2001; Reynolds et al., 2007). Shading changes the quality of light reaching the understory canopy (Krueger, 1981). Since overhead canopies absorb both the longest and shortest wavelengths of the light spectrum (red and blue), diffuse radiation is primarily composed of medium‐wavelength light (orange, yellow, and green). Growth regulating hormones and, therefore, growth are influenced by the interactions of the plant phytochrome system with red and infrared wavelengths (Baraldi, Bertazza, Bogino, Luna, & Bottini, 1995). Inadequate exposure to red light is known to influence stem production in clover (Trifolium sp.) (Robin, Hay, Newton, & Greer, 1994), tillering in grasses (Davis & Simmons, 1994a), flowering (Davis & Simmons, 1994b), and other basic plant growth processes (Sharrow, 1999).

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