Influence of pasture understoreys and tree management on soil moisture under a young New Zealand stand of Pinus radiata

Abstract

Soil moisture content (SMC) and throughfall were monitored along transects between rows of radiata pine (Pinus radiata D. Don) planted at 7 m row spacing and grown with ryegrass/clover or lucerne pastures or with no understorey. SMC was recorded to 1 or 2 m depths for years 2-6 or 4-6, respectively. The predominant rainfall from the south-south-west (SSW) direction created rain shadows (60% of open pasture) on the northern sunny side of the trees. The rain shadows increased as the trees grew but their position were modified by stand pruning and thinning in years 4 and 5. SMC in the top meter showed strong positional effects with the lowest SMC under the tree crowns and on the northern side. There were strong seasonal patterns driven by high spring and summer evapotranspiration, modified by rain shadows and stand age. For the no-understorey treatment, SMC remained high midway between tree rows until the trees were 4 years old and started utilizing this moisture. For the two pasture understoreys, the difference in SMC between the north and south sides decreased with time after trees were thinned and pruned. In the no-understorey there was little difference between the two aspects. Understorey evapotranspiration and fine rooting patterns also helped explain soil moisture use patterns. No difference was detected between two contrasting radiata pine tree types. The effective rooting depth of the ryegrass/ clover understorey was <0.7 m while that of lucerne and trees were deeper. Alternative tree planting practices may reduce some of the negative effects of tree-understory moisture competition.

Soil moisture and water use by pastures and silvopastures in a sub-humid temperate climate in New Zealand

“…This study, and a parallel study (Pollock and Mead 2008) which identified very dry zones close to the trees, particularly on the N sides, showed that recharge of the full soil profile was not always achieved over winter. Thus the benefits of the deep rooting lucerne were not always maximized in years of normal or subnormal rainfall nor would the benefit be realized if the lucerne silvopasture was on a shallow or coarse, free draining soil.…”

Using vector analysis to understand temporal changes in understorey-tree competition in agroforestry systems

“…Chang and Mead (2003) reported on tree growth and form from 1991 to 1998, and Yunusa et al (1995), Pollock and Mead (2008) and Pollock et al (2009) reported on soil moisture and water use of selected understorey and pine combinations at the same site as this investigation. Lucerne and phalaris were the most competitive understoreys by reducing height and diameter (at breast height) growth, followed by cocksfoot and clover, then ryegrass and clover, with ryegrass alone as the least competitive.…”

“…Data on soil and foliage nutrients, fascicle and tree growth (Chang and Mead, 2003) and soil moisture (Yunusa et al, 1995;Pollock and Mead, 2008;Pollock et al, 2009) are all now available to evaluate the utility of vector analysis to discriminate, with time, understorey competition between soil nutrient and moisture and its effects on the trees.…”

Effect of four plant species on soil 15N-access and herbage yield in temporary agricultural grasslands

“…15 N-access of individual plant species All species in the different experimental plant communities were able to access 15 N from all depths, even from 1.2 m. This surprised us, as the effective rooting depth of perennial ryegrass and white clover has been reported to be <0.7 m (Kutschera and Lichtenegger 1982;Kutschera and Lichtenegger 1992;Pollock and Mead 2008) and down to 1 m under drought stress conditions (Høgh-Jensen and Schjoerring 1997;Skinner 2008). In our study, relatively dry soil layers down to 0.8 m could possibly have stimulated deeper root growth and can therefore explain 15 N-access from deep soil layers for shallowrooting plant species.…”

“…To improve soil N use efficiency in temporary grasslands, we propose the addition of deeprooting plant species to a mixture of perennial ryegrass and white clover, which are the most widespread forage plant species in temporary grasslands in a temperate climate (Moore 2003). Perennial ryegrass and white clover possess relatively shallow root systems (Kutschera and Lichtenegger 1982;Kutschera and Lichtenegger 1992) with effective rooting depths of <0.7 m on a silt loamy site (Pollock and Mead 2008). Grassland species, such as lucerne and chicory, grow their tap-roots into deep soil layers and exploit soil nutrients and water in soil layers that the commonly grown shallow-rooting grassland species cannot reach (Braun et al 2010;Skinner 2008).…”