Role of weeds in the management of nitrogen in a young Pinus radiata plantation

Abstract

Application. Weeds in young Pinus radiata plantations can greatly retard tree growth by competing for mineral N . Although tree growth will be improved by maintaining a plantation weed-free or by adding N fertilizer, high N supply can induce stem deformation . Partial weed control may benefit productivity in the long-term because weeds reduce leaching of N .Abstract. Pinus radiata trees were grown on a podzolized sandy soil at a second rotation site under the following treatments: total weed control, total weed control plus ammonium nitrate, strip weed control and no weed control. During the first two summers after planting the differences in needle water potential between trees under no, strip or total weed control were very small . Despite similar rates of net N-mineralization in strip and total weed control treatments, which averaged 64 kg ha ' yr ' in the 0-15 cm soil depth, weeds in the strip weed control treatment reduced soil mineral-N concentrations by 50-80%, leaching of N by the end of the first growing season by 45%, foliar-N concentrations by 4-14% and stem biomass at 20 months after planting by 46% . Although N-uptake by above-ground vegetation (trees plus weeds) was 49% higher in the strip weed control treatment, the amount of N apportioned to trees during the first 20 months after planting was reduced from 15 .5 to 9.0 kg ha' . These effects of weeds were even more pronounced in the no weed control treatment . Since weeds had little effect on the needle water potential of trees and the annual rates of N-mineralization, but adversely affected N-uptake by trees, results indicate that weeds directly competed with trees for N, and thereby aggravated N-deficiency in trees . Application of ammonium nitrate after complete weed control increased foliar-N concentrations, and N-uptake and growth of trees, but also induced severe stem deformation .

Effects of weed control and fertilization on soil carbon and nutrient pools in an exotic pine plantation of subtropical Australia

“…This suggests that total and labile N parameters varied as a result of weed biomass. Smethurst and Nambiar (1989) and Woods et al (1992) recognized the pros and cons of N immobilization by weeds in plantations. Principle components analysis at both sampling positions in the 0-5-cm soil depth also indicated a significant contribution of labile N (NO 3 --N and NH 4 + -N), δ 15 N, and HWETN to the variation in soil nutrient patterns.…”

“…Despite the reasons for the plantation management decisions, sustaining and investigating the soils productive capacity has become a priority which is now formally endorsed around the world by the plantation certification, forestry standards, and global climate change research (Weil and Magdoff 2004;Xu and Chen 2006). The effects of weed control and fertilization to maximize growth and encourage the efficient use of nutrients could therefore be summarized not only by their contribution to the plantation productivity but also by how they affect soil processes during the earlyage, establishment phase (Smethurst and Nambiar 1989;Woods et al 1992), as has been done in the past with other forest management practices (Vitousek and Matson 1984;Xu et al 2008Xu et al , 2009. Contemporary research on this subject shows a complexity of results due to the nature of soils (Jobbagy and Jackson 2001).…”

The effect of multi-nutrient fertilization on understory vegetation nutrient concentrations in inland Northwest conifer stands

“…Over time fertilization may cause a change in species composition (Chapin et al, 1986) that will promote a more productive understory resulting in a greater amount of litter added to a site for decomposition. This will result in conservation of nutrients and a slow release ''fertilization'' over a long period of time after fertilization due to decomposition and a continual cycle of uptake and decomposition (Haines and Haines, 1979;Flanagan and Van Cleve, 1983;Miller et al, 1989;Smethurst and Nambiar, 1989).…”

Soil nitrogen mineralization and fate of (15NH4)2SO4 in field-incubated soil in a hardwood plantation of subtropical Australia: the effect of mulching

“…Many studies have addressed questions related to N availability in Australian forest soils (Smethurst and Nambiar 1989, 1990, 1995Carlyle 1995;Bubb et al 1998;Wang et al 1998;Blumfield and Xu 2003;Blumfield et al 2005Blumfield et al , 2006Xu et al 2008a, b), including N mineralization, nitrification, and leaching. These studies of N fluxes prompted the more effective use of N fertilizer in the region (Wang et al 1998;Xu 2006, 2008).…”