Shading effects of Pinus radiata on productivity and feeding value of cocksfoot pasture in an agroforestry system : A thesis submitted in partial fulfilment of the requirements for the degree of Master of Applied Science in Plant Science Group Soil, Plant and Ecological Sciences Division at Lincoln University Canterbury

Abstract

The shading effects of radiata pine (Pinus radiata D. Don) trees on productivity and feeding value of nine-year-old cocksfoot (Dactylis glomerata L) plus clovers (Trifolium spp) pasture on Templeton silt loam of medium fertility was measured under four light regimes in a sub-humid temperate climate at the Lincoln University agroforestry experimental area over four seasons from February 1998. The experiment was a randomised split-plot design with three levels of shade under trees as main plots and ± water applied to cocksfoot cv Grasslands Wana pasture areas with or without sheep urine patches as sub-plots in each of three blocks. In an adjacent open pasture plot of the same age, four sub-plots were randomly assigned to each of three blocks.

Photosynthetic photon flux density (PPFD) measured under radiata pine trees was 18% of full sunlight at 650 trees ha⁻¹, 40% at 300 trees ha⁻¹ and 67% at 200 trees ha⁻¹ compared with the ambient PPFD of adjacent open cocksfoot pasture. Tree shade reduced soil temperature at 100 mm soil depth in summer by 0.9-1.9°C and increased it in winter by 0.5°C under moderate shade (40% to 67% PPFD) compared with open pasture with 20.5°C summer and 5.8°C winter mean temperatures. Likewise, volumetric water content (%) at 0-300 mm soil depth under 18% and 40% PPFD was significantly lower in late autumn, winter and spring seasons and higher during summer under 18% PPFD. Under 40% and 67% PPFD there was more soil water only in January compared with open pasture which had 30.9% and 9.8% soil moisture in June and January respectively. Partial irrigation reduced soil temperature significantly in late spring, summer and autumn and increased soil water content in summer under trees by only 1.3% and in open pasture by only 0.8% compared with unirrigated plots.

Botanical composition, expressed as percentage cover of nine-year-old Wana cocksfoot plus clover pasture along permanent transects in open pasture was 83% cocksfoot, 4% white clover, 1 % subterranean clover, 5% weeds, 1 % dead material and 6% bare ground compared with 74% cocksfoot, 3% white clover, 4% subterranean clover, 4% weeds, 5% dead material and 10% bare ground under trees with 67% ambient PPFD.

The five, 30 day production periods in March, June, September and November 1998, and February 1999 showed that cocksfoot pasture production at 18% PPFD was reduced by 55% even in irrigated urine and non-urine patches compared with open pasture. In this heavy shade, cocksfoot pasture productivity and feeding value was reduced by tree shade. However, under 40% and 67% PPFD pasture production without irrigation in urine and non-urine patches in the very dry 1998/99 season was reduced by 30% and 21 % compared with open pasture which yielded 319 g DM/m² and by 16% and only 1% with irrigation (520 g DM/m² over the five months in irrigated open pasture).

The apparent feeding value of shaded cocksfoot pasture was reduced because of changes in grass morphology (longer and thinner leaves) of shaded pasture which resulted in reduced pasture bulk density which may reduce pasture intake through smaller bite size. This possible adverse effect on intake together with reductions in the nutritive value (digestible organic matter, nitrogen and metabolisable energy) of shaded pasture could result in reduced per head animal performance. However, the small (4%) increase of clover content and the decrease (29%) in reproductive tiller numbers under 40 to 67% PPFD may partially compensate these adverse effects in spring and early summer compared with open pasture.

Results showed that cocksfoot pastures under moderate shade (40% to 67% PPFD) were more stressed by water and nitrogen than by tree shade because the addition of water and nitrogen (urine) under moderate shade gave large increases in pasture production, pasture bulk density and nutritive value compared with the nil treatment pasture areas.