New Zealand Journal of Agricultural Research abstracts

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A soil sampling protocol to minimise the spatial variability in soil test values in New Zealand hill country

J. D. MORTON

AgResearch
Invermay Agricultural Centre
Private Bag 50034
Mosgiel, New Zealand

D. B. BAIRD

AgResearch
Canterbury Agriculture and Science Centre
Private Bag 20
Lincoln, New Zealand

M. J. MANNING

Ravensdown Fertiliser Co-operative Ltd
P.O. Box 9815
Newmarket, Auckland

Abstract  Because of the large inherent changes over time and space, non-systematic sampling in hill country can result in high coefficients of variation (CV 18-55%) in soil phosphorus (P), sulphur (S), and potassium (K) levels between measurements. The components of spatial variability were measured on 20 hill-country sheep and beef farms. For Olsen P, 38% of the total farm variance was measured within 1 m of a fixed point, 27% within 100 m, and 35% between paddocks within a farm block. With soil pH, quick test K, and sulphate S, there was greater variation within 1 m, less within 100 m, and very little between paddocks, compared with Olsen P. From this information, a sampling protocol was designed to achieve the target CV for Olsen P (15-20%).

The sampling protocol was tested on 77 hill-country farm blocks. At annual intervals up to 5 years after establishment, 100 m transects from within 3 representative paddocks were re sampled at 10-m intervals from within a 0.3-m radius of each original sampling position. All soil cores from the 3 transects except those at each end were bulked (n = 27) for one block. Over 4 years on average, the mean CV for change in Olsen P between years was 21.3%. Corresponding CVs for soil pH were 2.2%, soil sulphate S 37.4%, and soil quick test K 26.2%. These results indicate that the use of a scientifically designed and robustly tested soil sampling protocol will minimise the variability in measured soil Olsen P, pH, and other soil test nutrient levels in hill country over time and allow more accurate advice to be provided on fertiliser nutrient requirements.

Keywords  soil; spatial variability; time; pH; sampling; Olsen P; sulphate S; quick test K; coefficient of variation

New Zealand Journal of Agricultural Research, 2000, Vol 43: 367-375

0028-8233/00/4303-0367 $7.00/0 (c) The Royal Society of New Zealand 2000

PDF file of entire paper: medium quality (633K); (scanned from paper original: notes about this process)

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