Alleviating the Problem of Upland Saline Sodic Soil with Fragipan for Growing Cassava

Abstract

The effects of tillage using a ripper plough to the depth of 40 cm and conventional land preparation combined with the application of soil conditioners—gypsum and limestone at the rate of 200 kg/rai, cow manure at the rate of 1000 kg/rai, and mycorrhiza at the rate of 2 g/plant—on the changes to soil properties and yields of cassava, var. Huay Bong 80 grown on an upland saline sodic soil (Fragic Natrustalf) with an occurrence of fragipan was conducted. The use of the ripper tended to better enhance the growth of cassava, particularly in the second year, in which fresh tuber yield was significantly higher compared with that of no rippering, with the respective yields of 2.5 and 2.1 t/rai in the first year, and 3.4 and 2.4 t/rai in the second year. The application of soil conditioners tended to give higher cassava yield and above-ground biomass than those of no application. Although the addition of cow manure and mycorrhiza tended to give lower fresh tuber yield in the first year; it, except for mycorrhiza that was not applied, clearly tended to increase yields from 1.9 to 3.1 and 1.6 to 2.5 ton/rai, respectively. However, the application  of cow manure and mycorrhiza tended to induce lower starch percentage than the use of gypsum and ground limestone. The highest statistically significant fresh tuber and starch yields of 4.3 t/rai and 824 kg/rai, respectively, were obtained when applying gypsum combined with deep tillage using the ripper. No rippering and no application of soil conditioners gave the lowest fresh tuber weight of 1.7 t/rai. The use of the ripper and the application of soil conditioners for two consecutive years tended to improve soil physical properties by reducing bulk density, increasing available water capacity, and diminishing the problem of salinity and sodium, especially when gypsum was applied. Moreover, the addition of cow manure helped retain more organic matter and plant nutrients in the soil than those of other soil conditioners.