英语翻译La data obtained in 1997 and 1998 only for some depths w
英语翻译
La data obtained in 1997 and 1998 only for some depths were significantly different respect to the position of the drip irrigation tube,cultivar or interaction between depth of the irrigation tube and cultivar (Tables 5–8).This outcome was probably associated to the high variability of La values,as confirmed by the variation coefficients of the ANOVA,which ranged between 10 and 80%.Great spatial root variability is associated with interaction between root system structure and soil conditions and has been documented by many authors (Brown and Scott,1984; Hamblin,1985; Oliveira et al.,2000; Upchurch,1987; Van Noordwijk,1993; Zobel,1991).Variability may also be associated to the method used.Vos and Groenwold (1987) reported a coefficient of variation of 1.5–1.7 times greater for minirhizotrons than for core sampling.However,the minirhizotron method allows a greater number of replications and is less labour-intensive than core sampling.Bar-Yosef et al.(1991),using soil coring,obtained similar results when comparing subsurface versus surface drip irrigation and they also could not find an unequivocal relationship between treatments and root distribution.Despite the lack of significant differences between treatments based on minirhizotron analysis,the distribution of the root system,in relation to the placement of the drip irrigation tube (Figure 1),observed on soil profiles opened perpendicularly to the plant row,show different rooting patterns among irrigation treatments.A large concentration of roots at the depth of the irrigation tubes was found,which is in agreement with the observations reported for tomato under subsurface drip irrigation by Bar-Yosef et al.(1991),for maize by Mitchell (1981) and Phene et al.(1991) and for cotton by Plaut et al.(1996).