4. Discussion
The study found that switching from balanced to intensive cropping is not simply adding a third crop. It changes the character of the whole farming system in terms of cultivation conditions, water management, cropping calendar, and so on. These changes, in turn, imply different required input combinations to be able to achieve similar yields across the two systems (Tables 3 and 4). For example, with three continuous crops, “bridges” between each crop exist through which insects and diseases are transmitted throughout the cropping year and cause organic acid poisoning of rice crops at the cropping time as a result of the shortened rice straw decomposition process (Nguyen, 2012; Nguyen et al., 2015). Switching to rice varieties with higher levels of resistance to diseases and insects is then a likely solution of intensive cropping farmers in dealing with such unfavourable conditions (Table 3). A change in rice variety could also be one of the factors that alter fertiliser application needs (Table 4). There is also evidence that intensive cropping has spillover effects on adjacent areas. This is seen in the lower quantities of insecticides used per crop in intensive cropping compared to that applied in contiguous balanced cropping sites (Table 4). As mentioned, intensive cropping farmers have switched to rice varieties with high resistance to insects (see Table 3). As a result, contiguous balanced cropping with more vulnerable rice varieties serves as an extra feed source for insects originating from intensive cropping sites, thereby requiring farmers in balanced cropping sites to apply more insecticides. The spillover effect of intensive cropping is also seen in the significantly high levels of molluscicides applied by contiguous balanced cropping farmers per crop (Table 4). As previously indicated, this could be the solution of balanced cropping farmers in dealing with the abundant of golden apple snails diverted from high-dyke areas to low-dyke areas (Fig. 2)
