SUMMARY Among the soil amendments, peat has the advantages of promoting a very good top growth and dense root system, when properly irrigated to avoid poor aeration. It has the disadvantages of not being able to withstand compaction and can become excessively wet if proper irrigation practices are not followed. Lignified wood has the advantages of withstanding compaction, providing high infiltration rates, allowing good aeration, maintaining an extended supply of nitrogen under leaching conditions, and promoting a good root system under a high oxygen diffusion rate (ODR). It has the disadvantages of contributing to soil salinity, and apparently requires a higher ODR for maximum root growth. Calcined clay has the advantages of withstanding compaction, providing high infiltration rate and allowing for good aeration. Its disadvantage is that although it promotes deep roots, they are rather sparse with few roothairs. Better results were obtained with irrigation based upon tensiometer records than by irrigation according to a set calendar schedule. Advantages over the set program chosen for this experiment included a savings in water, improvement in soil aeration, and reduction in soil compact ability. One requirement in irrigating by tensiometer records is that excess water must be applied periodically to cause leaching, if salinity becomes too high. The wetting-agent treatment (at only 3 ppm), increased the infiltration rate of the unamended soil, reduced compactability of peat-amended soil, and also resulted in some other effects of minor significance. Other research in progress indicates that the relationships between wetting agents and plant growth are extremely complex, and no general conclusions are likely for some time.

The Emery Corporation, Southern California Turfgrass Council, and Loamite Division of Pope and Talbot Corporation assisted in financing this project.