USE OF SOIL PENETRATION RESISTANCE AND GROUP METHOD OF DATA HANDLING TO IMPROVE SOIL-WATER RETENTION ESTIMATES

The accuracy of pedotransfer functions can be improved using more flex ible equations and additional input variables. Penetration resistance as a parameter related to soil structure can be a useful additional in put to pedotransfer functions. Our objectives were to see whether usin g penetration resistance can improve the accuracy of estimating water retention from soil composition and bulk density. To develop pedotrans fer functions, we applied group method of data handling (GMDH) resulti ng in hierarchical polynomial regression networks or abductive network s. The advantage of GMDH is that it automates finding essential input variables to be included in pedotransfer functions and, unlike the art ificial neural networks (ANN), presents an explicit form of the equati ons. We developed pedotransfer functions from data on texture, bulk de nsity, penetration resistance, and water content at 0, -5, -10, -20, - 100 and -1500 kPa in 180 samples of soils in New Zealand, Abductive ne tworks were used to estimate water content at particular matrix potent ials. The water content at -1500 kPa and the penetration resistance we re the essential variables to include in pedotransfer functions along with bulk density and texture. The pore volume fractal dimension could be reliably estimated from the water content at -1500 kPa and penetra tion resistance. The variation coefficient rather than average value o f penetration resistance was found to be a good predictor in some case s. (C) 1998 Elsevier Science B.V. All rights reserved.