Comparison of single and double cropping of rice on the physical properties in relation to tillage of a vertisol

A number of so i I physical properties in relation to tillage were assessed under no cropping, single cropping and double cropping of lowland rice on a vertisol in the Kano plains of Western Kenya. The investigation of physical properties took place on soil samples of 0-15 cm, 15-30 cm, 30-45 cm, 45-60 and 60-75 cm depths. The study revealed that al I the sites had high clay content <> 60%) therefore belonged to a clay t ex t u r a I c Iass. These were classified agronomically as heavy soils. These soils are good for lowland rice growing but difficult to cultivate for an Upland crop and take long to dry increasing the turnaround time between rice and an Upland crop. Comparison of the management systems revealed no significant porosity. compaction compaction changes in bulk density and total These compaction indices and relative values calculated confirmed no soil under double cropping despite increased passage of the cultivation machines. Lack of compaction was attributed to the soils high propensity for structure recovery.This makes them suitable for double cropping of rice. Maximum dry density values xv obtained ranged from 1.29 to 1.33 gm/cm 3 and were termed low hence the soils suitability for Upland crop production. Cropping intensity lowered organic carbon content which subsequently lowered the soil's plastic limit reducing the soils friability range. Liquid Ii m it increased within the top 45 cm depth. The combination of reduced plastic limit and increased liquid I i m it widened the Plastic Index increasing the moisture content range at which the soils remain plastic. Double cropping treatment was found to have low soil strength at the 15-30 cm depth throughout al I the effective normal stress. This was suspected to be the cause of tractor sinking. Single cropping treatment was found to have high shear strength tha t was attributed to the lo n g e r drying periods, wh i Ie cropping was found to have increased water stability of aggregates.