Soil quality monitoring and evaluation under conventional plow-based and conservation agriculture production systems in southern Philippines

Soil quality under conventional plow-based agriculture production systems has been known to degrade over time owing to greater exposure of soil organic matter to microbial attack. This study was conducted to monitor and evaluate soil quality under conventional plow-based and conservation agriculture production systems (CAPS) in southern Philippines. Six CAPS treatments in the form of cropping patterns with different cover crops under two fertility levels including plow-based system were established and laid out in a randomized complete block design in a typical upland agricultural producing area in Claveria, Misamis Oriental, Philippines. Soil sampling was performed at three depths (0-5 cm, 5-10 cm and 15-30 cm) at the experimental site in July 2010, December 2010, April 2011 and September 2011. The soil samples collected were brought to University of the Philippines Los Baños for physical and chemical analysis. The observed values of bulk density, soil organic matter, soil nitrogen, soil phosphorus and soil pH at various CAPS treatments were consequently analyzed. The residual soil moisture content was also measured at the various plots of the CAPS treatments at the site using time domain reflectometry (TDR). Results showed that differences in soil quality parameter values were observed over time and at various depths for the various CAPS treatments, although the observed differences over time did not appear to be substantial after one year of cropping. The soil organic matter at the uppermost soil layer (0-5 cm) did not exhibit a well-defined pattern of temporal variation although the organic matter under conventional plow-based system appeared to decline slightly over time. Both soil nitrogen and phosphorus concentrations in all CAPS treatments were generally higher in the upper soil layers (0-15 cm) than in the deeper soil layers (15 to 30 cm) under the two fertility levels. The soil bulk density remained practically the same as the baseline conditions for all soil layers. Analysis of variance of the residual moisture during the dry month of April 2011 showed that the plots under conservation agriculture have significantly higher residual moisture content than under conventional plow-based system with maize+Stylosanthes guianensis-Stylosanthes guianensis- fallow CAPS treatment exhibiting the highest residual moisture content level. Additional soil quality monitoring is necessary to generate empirical evidence on the effect of conservation agriculture on soil quality improvement. All these findings could then serve as basis for future assessment of the impacts of conservation agriculture and conventional plowbased systems on soil quality.