SOIL ph AND NUTRIENT LEVELS AT TIKITERE AGROFORESTRY RESEARCH AREA

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1 SOIL ph AND NUTRIENT LEVELS AT TIKITERE AGROFORESTRY RESEARCH AREA M.F. HAWKE AgResearch, P.O.Box 1, Rotorua, New Zealand and M.B. O'CONNOR AgResearch, Ruakura Agricultural Centre, Private Bag 1, Hamilton, New Zealand (Received for publication 1 November 1; revision June 1) ABSTRACT Soils under various stockings of Pinus radiata D.Don at the Tikitere Agroforestry Research Area near Rotorua have shown a significant decline in soil ph with increasing tree age and at higher tree stockings. Soil ph levels in 1 (year ) for,1,, and stems/ha were.,.,., and. respectively, compared with.,.,., and. in 11. Higher phosphorus and sulphate-sulphur levels under trees and an increase in magnesium on open pasture were also evident. A soil profile study at year 1 indicated ph reductions to mm depth, with increasing phosphorus levels to mm depth. Sulphate-sulphur levels increased at all depths in stems/ha plots. Keywords: agroforestry; needles; ph; soil nutrients; fertiliser; pasture; Pinus radiata. INTRODUCTION The New Zealand exotic forest crop area totals 1. million ha (Sutton 11) and there are predictions of up to 1 ha of new land being planted each year, most of which will be farmland because of the increasing profitability of forestry and the reduced availability of land classes previously used for afforestation. There is also evidence that mean basal area growth of young Pinus radiata on farm sites is up to % greater than on forest sites (Knowles & West 1). There have been reports from overseas (Goldsmith 1) that planting pines leads to soil acidity. However, there has been no evidence that this has occurred on New Zealand sites (Dyck et al. 1) and an earlier report from Tikitere at tree age years did not show this trend (Percival et al. 1). Cockayne (1) and Will & Ballard (1) observed that P. radiata crops improved soil fertility. Jurgensen et al. (1) commented that the effect of introduced forest species on soil properties has received relatively little attention in New Zealand, in spite of the large areas of new planting. The Tikitere Agroforestry Research Area near Rotorua was planted in P. radiata at a range of tree stockings in 1 and soil fertility parameters have been monitored for 1 years. This paper presents the data from this study. New Zealand Journal of Forestry Science (1): - (1)

2 Hawke & O'Connor Soil ph and nutrient levels 1 SITE DESCRIPTION AND TRIAL DESIGN The trial was on a recent volcanic sandy loam (typic Vitrudand) classified as Rotoiti sandy loam. It was on flat to moderately steep land with a mean annual rainfall of 1 mm, generally evenly distributed. The site had a - year history of pastoral landuse. Pinus radiata was planted at stockings of,,, 1, and stems/ha. Each stocking treatment covered ha in four -ha replicated blocks, surrounded by a -m buffer zone. Initial stocking rates were reduced over an -year period to final stockings of,,1,, and stems/ha (McQueen et al 1). Fertiliser History The initial objective was to maintain adequate soil nutrient status across all treatments. However, once pasture production decreased substantially, usually at canopy closure, fertiliser applications ceased. Tikitere was aerially topdressed annually from 1 to 1 at - kg/ha with either % or % potassic superphosphate. Potassic serpentine superphosphate was applied in 1 and 1. Plots on steep land received an additional kg superphosphate/ha annually from 1 to 1. Lime ( t/ha) was applied to one stems/ha plot with low ph in 1 and cobalt sulphate (- g/ha) was included in the main topdressing every second year. Topdressing ceased in 1 (year 1) on the stems/ha plots, in 1 on the stems/ ha, and in 1 on the 1 stems/ha. In 11 and 1, kg cobaltised superphosphate/ ha was applied by ground spreading to the and stems/ha plots. When all stocking treatments were receiving fertiliser (1-) the nutrients applied annually were phosphorus -1 kg/ha, potassium 1- kg/ha, sulphur - kg/ha, and magnesium -1 kg/ha. Grazing Management At Tikitere, sheep were rotationally grazed from 1 to 1. In the stems/ha treatment there was little pasture remaining after year and stock had only periodic access to that treatment after 1. A similar trend occurred with the stems/ha plots after 1. Since 1, the research area has been grazed as one paddock with breeding ewes and beef cows. Measurements Soil samples were taken at random within plots using a standard -mm-diameter corer. Usually - samples per plot were collected below the decomposing needle layer. Care was taken to ensure that areas around troughs, gateways, fences, and stock camps were not sampled. Measurements were made of ph, calcium, phosphorus, potassium, and magnesium using the Ministry of Agriculture and Fisheries Quicktest procedures (Cornforth 1), and phosphate extractable sulphate (Saunders et al. 11). Samples were taken at - mm depth at years,,,,,,,,, and 1, usually in May. In 1, at year 1, samples were taken at depths of -,-,-, and - mm in all treatments. Analysis for sulphate-sulphur commenced in 1. Bulk density samples were taken in March 1 for one replicate paddock in each tree stocking treatment, and the weight of each nutrient in the - mm soil layer was calculated. The data were analysed using standard analysis of variance procedures.

3 New Zealand Journal of Forestry Science (1) RESULTS PH Soil ph levels have remained relatively constant in the open pasture and stems/ha treatments. There has been a trend emerging since year of decreasing ph levels at the - mm depth with higher tree stockings (Table Ia). At stems/ha from year and at stems/ha from year 1, reductions in ph were significant (p<.). Reductions in ph at and 1 stems/ha were statistically non-significant. The samples taken at a series of depths at year 1 showed statistically significant reductions at 1 stems/ha and higher tree stockings, down to mm. At stems/ha, there was also a reduction at - mm (Table Ib). TABLE la-effects of tree stocking and stand age on soil ph levels at - mm depth Tre< stocking (si:ems/ha) TABLE lb-soil ph levels at increasing depth at; year 1 -S Calcium There was a reduction (p<.) at years and 1 (Table a) in the stems/ha plots and at year 1 in the stems/ha for the - mm depth. Calcium levels declined with increasing depth (Table b) and there were reductions (p<.) down to - mm at stockings greater than stems/ha. Phosphorus A definite trend of increasing phosphorus levels at higher tree stockings has been evident from year onwards (Table a), being statistically significant at 1 stems/ha upwards from year. The quantity of available phosphorus in the - mm depth at year 1 increased at stockings up to 1 stems/ha (Table ) and this trend was noticeable down to - mm (Table b). Potassium Potassium status has remained relatively static at all tree stockings since year (Table a), although levels at the higher tree stockings were slightly reduced from year onwards. At

4 Hawke & O'Connor Soil ph and nutrient levels TABLE a-effects of tree stocking and stand age on Quicktest soil calcium levels (ppm) at - mm depth TABLE b-quicktest soil calcium levels (ppm) at increasing ; depth at year TABLE a-effects of tree stocking and stand age on Olsen soil phosphorus levels (ppm) at - mm depth * * 1 * * *. *Truog phosphorus 1* * 1* * *... TABLE b-1sen soil phosphorus ; levels at increasing depth at year year 1 there was no consistent trend by depth or tree stocking rate (Table b) or in the quantity of potassium in the - mm depth (Table ).

5 New Zealand Journal of Forestry Science (1) TABLE -Quantity of nutrients in the - mm soil layer at year 1 Nutrient (kg/ha) 1 * Olsen phosphorus t Quick-test Phosphorus* 1 1 Potassiumt 1 1 Magnesiumf 1 1 Sulphate-sulphurt TABLE a-effects of tree stocking and stand age on Quicktest soil potassium levels (ppm) at - mm depth "o Tf TABLE b-quicktest soil potassium levels (ppm) at increasing depth at year Magnesium Levels remained relatively constant up to year, but since then have increased on open pasture and at the lower tree stockings, while the levels in the and stems/ha plots have remained constant (Table a). At year 1 these differences were evident in the - mm sample (Table ) and at - mm depth, but not in the deeper layers (Table b). Sulphate-sulphur Sulphate-sulphur levels were measured from 1 onwards. Although absolute values fluctuated between years, sulphate-sulphur levels tended to increase at higher tree stocking rates and at increasing soil depth down to mm (Tables a and b). The increase at higher tree stockings was evident in the quantity of sulphate-sulphur in the - mm samples (Table ).

6 Hawke & O'Connor Soil ph and nutrient levels TABLE a-effects of tree stocking and stand age on Quicktest soil magnesium levels (ppm) at - mm depth (stems/ha] TABLE b-quicktest soil magnesium levels (ppm) al t increasing depth at year 1 Ti ree stocking i TABLE a-effects of tree stocking and stand age on Quicktest soil sulphate-sulphur levels at - mm depth 1. TABLE b-quicktest soil sulphate-sulphur levels (ppm) at increasing depth at year DISCUSSION ph The measured changes in soil ph at Tikitere support associated studies on this site. Analyses of regular samples taken to mm depth revealed marked reductions at stems/

7 New Zealand Journal of Forestry Science (1) ha from year (Hawke, unpubl. data). Yeates (1) reported significant reductions at and stems/ha at years and at - mm depth. Sparling et al. (1) reported a significant reduction only at stems/ha in year. However, at other agroforestry research sites in New Zealand planted with P. radiata, ph reductions were not apparent. The Whatawhata trial near Hamilton is at year 1, and yet ph levels remain at about.-. over the 1- stems/ha range (I.L.Power, pers. comm.). At the Otago Coast Forest, the agroforestry trial at year had a level of.1-. over the - stems/harange (G.G.Cossens & G.S.Crossan unpubl. data). As those levels are lower than the. starting level at Tikitere, further reductions in ph would be unlikely on those sites. The initial soil ph values at Tikitere, however, are likely to reflect a large proportion of the central North Island pastoral land with potential for tree plantings. In maturing forest plantations in New Zealand, fertility has rarely been monitored by soil testing (McLaren & Cameron 1) and so there is no database for comparison. Studies in Western Australia have reported no changes in ph levels under young P. radiata agroforestry plantations up to year (Anderson & Moore 1). However, in Britain, Ovington & Madg wick (1) reported that soil ph was reduced by afforestation with conifers and that the greatest change occurred within the first years after planting. Decaying pine needles at Tikitere had a ph of. and the decomposing organic layer a ph of. (Hawke unpubl. data). This suggests that pine needles could be affecting soil ph. Ovington (1) noted that plots of Pinus spp. showed an upper zone of increased acidity compared to open pasture, and this zone extended to about mm depth. Needlefall can be quite substantial and annual amounts of and kg dry matter/ha have been recorded in 1 and stems/ha plots respectively at year at Tikitere (Hawke, unpubl. data). Needlefall and the production of organic anions are likely to be the main cause of acidification at Tikitere. Other studies at Tikitere (Yeates 1) have suggested that changes in soil biological activity and declining earthworm numbers are associated with a fall in soil ph. Calcium Soil Nutrient Levels Calcium status showed a similar trend to soil ph levels. Phosphorus The high phosphorus levels measured under P. radiata are supported by data from the Purukohukohu Catchment (Cooper, unpubl. data) comparing soil chemical parameters under pasture and pine plantations. Higher phosphorus levels under trees were also evident at the Whatawhata and Otago Coast trials (pers, comm.) and have been reported in pine plantations at Lake Coleridge in Canterbury (Davis 1). Nutrient cycling in a forestry system is very efficient, with only 1-% of the nutrients taken up by the trees becoming immobilised and the rest being returned via the litter or from canopy leaching (McLaren & Cameron 1; Will 1). There are also reduced demands on soil nutrients in the latter part of the tree crop's growth (Will 1).

8 Hawke & O'Connor Soil ph and nutrient levels Potassium The relatively static potassium levels under trees confirm that recycling processes are very efficient. On open pasture, nutrient cycling by animals together with addition of potassium fertiliser have maintained levels over time. Magnesium The maintenance of reserves of magnesium in the soil under P. radiata supports previous studies in New Zealand (Will 1) and Australia (Hopmans et al. 1). There was no evidence of any treatment effect at Whatawhata (unpubl. data), but in the Otago Coast trial the trend followed the Tikitere pattern (G.G.Cossens & G.S.Crossan unpubl. data). The high magnesium value on open pasture at Tikitere at year 1 is unexplained. Sulphur The reduction in sulphate-sulphur levels between 1 and 11 suggests that considerable leaching was occurring and that sulphate has not been adequately replaced by sulphur fertilisers (Ledgard et al. 11). Prior to 1, there was a regular superphosphate fertiliser application. Between 1 and 11 fertiliser was applied only to the and stems/ha treatments. In spite of this, the levels in the 1- stems/ha treatments were higher. CONCLUSIONS At Tikitere there has been significant decline in soil ph levels at tree stockings above stems/ha. These effects became evident from year onwards, i.e., in the second half of the tree production rotation. The decline in soil ph has implications for future land use on agroforestry areas. If the area were to be replanted in forest trees, i.e., a second rotation, there should be little problem but if it were to be returned to pastoral agriculture, a liming programme would be required and possibly legume inoculation and earthworm introduction. Agroforestry plantations, on the other hand, have generally positive effects on soil nutrient levels. Phosphorus, potassium, sulphur, and magnesium (as measured by Olsen and Quicktest procedures, respectively) have all increased or remained at adequate levels for subsequent pastoral agriculture use (Cornforth & Sinclair 1). ACKNOWLEDGMENTS The authors wish to thank Mr Tom Gee for much of the field work, Messrs I.P.M.McQueen and N.S.Percival for the preliminary investigations, Dr J.Waller and Miss B.Dow for biometrical analysis, the Ruakura Soil Fertility Laboratory for chemical analysis, and Mr M.Brown for nutrient element calculations. We also acknowledge the useful comments of Dr G.M.Will and Dr H.A.I.Madgwick. REFERENCES ANDERSON, G.W.; MOORE, R.W. 1: Productivity in the first seven years of a Pinus radiataannual pasture agroforest in Western Australia. Australian Journal of Experimental Agriculture : 1-.

9 New Zealand Journal of Forestry Science (1) COCKAYNE, A.H. 1: Pinus radiata plantations Effect on soil fertility. New Zealand Journal of Agriculture (): -1. CORNFORTH, LS. 1: Soils and fertilisers: Soil analysis interpretation. New Zealand Ministry of Agriculture and Fisheries, Wellington, AgLink FPP. CORNFORTH, LS.; SINCLAIR, A.G. 1: "Fertiliser and Lime Recommendations for Pastures and Crops in New Zealand". nd rev. ed. Ministry of Agriculture and Fisheries. p. DAVIS, M.R. 1: Influence of Pinus radiata seedlings on phosphorus availability in high country soils. Proceedings of the New Zealand Society of Soil Science: 1. DYCK, W.J.; WILL, G.M.; MESSINA, M.G. 1: The influence of radiata pine forestry on soil. Pp. - in Proceedings of the "Soil Dynamics and Land Use Seminar", Blenheim. GOLDSMITH, E. 1: A man of the trees. The Ecologist (): -1. HOPMANS, P.; FLINN, D.W.; SQUIRE, R.O. 1: Soil chemical properties under eucalypt forest and radiata pine plantations on coastal sands. Forests Commission, Victoria, Forestry Technical Paper No.: -. JURGENSEN,M.F.;FREDERICK,D.J.;MADGWICK,H.A.I.;OLIVER,G.R. 1: Soil development under Pinus radiata and Eucalyptus regnans plantations. New Zealand Journal Forestry Science 1(1): -. KNOWLES, R.L.; WEST, G.G. 1: The use of crown length to predict the effects of pruning and thinningin Pinus radiata. Pp. 1-1 in Proceedings of the Symposium on "Crown and Canopy Structure in Relation to Productivity". Forestry and Forest Products Research Institute, Ibaraki, Japan. LEDGARD, S.F.; JOHNSTON, T.J.M.; EDMEADES, D.C.; WHEELER, D.M. 11: Soil nutrient status of the Bay of Plenty region and the implications to pasture productivity and fertiliser requirements. Proceedings of the New Zealand Grasslands Association : -1. McLAREN, R.G.; CAMERON, Kr. 1: "Soil Science". Oxford University Press. Pp. -. McQUEEN, I.P.M.; KNOWLES, R.L.; HAWKE, M.F. 1: Evaluating forest farming. Proceedings of the New Zealand Grasslands Association (): -. OVINGTON, J.D. 1: Studies of the development of woodland conditions under different trees Part 1: ph. Journal of Ecology 1: -. OVINGTON, J.D.; MADGWICK, H.A.I. 1: Afforestation and soil reaction. Journal of Soil Science (1): 1-. PERCIVAL, N.S.; GEE, T.M.; STEELE, K.W. 1: Effects on soil fertility of Pinus radiata on farmland. Proceedings of Technical Workshop on Agroforestry, Dunedin: -. SAUNDERS, W.M.H.; COOPER, D.M.; SINCLAIR, A.G. 11: Soils and fertilisers: Sulphur. New Zealand Ministry of Agriculture and Fisheries, Wellington, AgLink FPP. SPARLING, G.P.; HART, P.B.S.; HAWKE, M.F. 1: Influence of Pinus radiata stocking density on organic matter pools and mineralisable nitrogen in an agroforestry system. Proceedings of Workshop on "Nitrogen in New Zealand Agriculture and Horticulture". Massey University, Occasional Report No. : 1-. SUTTON, W.R.J. 11: Does New Zealand need another million hectares of pines? NZIAS Convention Proceedings. WILL, G.M. 1: The uptake, cycling and removal of mineral nutrients by crops of Pinus radiata. Proceedings of the New Zealand Ecological Society : -. WILL, G.M.; BALLARD, R. 1: Radiata pine Soil degrader or improver? New Zealand Journal of Forestry 1(): -. YEATES, G.W. 1: Earthworm and enchytraeid populations in a -year-old agroforestry system. New Zealand Journal of Forestry Science 1(): -1.