Linking Tasmanian potato and poppy yields to selected soil physical and chemical properties

Selected soil properties and paddock management characteristics were measured for 121 potato and poppy crops in north and northwest Tasmania to see if variation in these characteristics explain variation in crop yield. The soil properties we selected were those that previous work found had changed the most as a result of cropping and, therefore, may be affecting yield on the particular soil type. The soil properties and management characteristics that were significantly correlated with crop yield varied with crop and soil type. None of the soil characters had correlation coefficients greater than 0.63, probably reflecting the capacity of individual farmers to overcome particular soil limitations through their management of tillage, nutrition, irrigation, weeds and pathogens. On ferrosols, a visual score of soil structure was significantly correlated with potato yield (r = 0.57) and exchangeable aluminium was significantly correlated with poppy yield (r = 0.63). Exchangeable calcium (r = 0.54) and penetration resistance (r = 0.38) correlated positively and topdressed nitrogen (r = –0.49) correlated negatively with poppy alkaloid assay, an important determinant of overall poppy yield. On dermosols, depth to 2000 kPa penetration resistance (r = 0.60) and fertiliser P (r = –0.67) were correlated with potato yield, structure score correlated with poppy yield (r = 0.59), and penetration resistance with poppy assay (r = 0.52). On sodosols, fertiliser K (r = –0.41 and r = 0.55) and N (r = –0.45 and 0.42) correlated negatively with poppy yield and positively with poppy assay. On clay loam soils such as dermosols and ferrosols, increased topsoil cloddiness appears to be having a deleterious effect on crop yield. Cloddiness is readily assessed on these soils using the structure scorecard, which could therefore become a practical diagnostic test for farmers and advisers.