Crop rotation of shrimp (Penaeus monodon) and milkfish (Chanos chanos)

The crop rotation technique was verified in two commercial farms located in Pulupandan, Negros Occidental and in Altavas, Aklan [Philippines]. Results showed that shrimp harvest, the soil pH (both wet and dry) in Pulupandan farm was slightly basic and stable, while that of the Altavas, Aklan farm was slightly acidic. The organic matter content was also stable, but decrease in the available phosphorus concentration was noted in the Pulupandan farm. In the Altavas, Aklan farm, slight increases in the concentration of organic matter and available phosphorus were observed. Both potential acidity and lime requirement of the ponds in Pulupandan were nil, while that in Altavas, Aklan increased in concentration after shrimp harvest. When the ponds in Pulupandan, Negros Occidental were alternately cropped with milkfish, the soil pH remained stable, but a decrease in the available phosphorus and organic matter concentrations of the soil was noted. The potential acidity and lime requirement were also nil. On the other hand, when the pond in Altavas was stocked with milkfish after shrimp culture, the soil pH was slightly acidic, but the organic matter and available phosphorus concentrations decreased. Furthermore, the potential acidity and lime requirement remained stable. However, when the soil parameters were fitted in a graph based on the readings monitored regularly, there seem to exist differences in the trends between the Pulupandan farm and that of the Altavas farm due to differences in the level of culture and the age of the farm. The Pulupandan farm which is already mature and utilizes the semi-intensive culture exhibited erratic trends in the different soil parameters monitored. On the other hand, the Altavas farm which is newly-build and which utilizes the modified-extensive culture system has slightly acidic pond soil. Furthermore, the organic matter and available phosphorus concentrations as well as the lime requirement and potential acidity increased toward the latter part of the shrimp culture cycle and again decreased after the milkfish culture cycle