Irrigation strategies to improve the water use efficiency of wheat-maize double cropping systems in North China Plain

Water is the most important limiting factor of wheat (Triticum aestivum L.) and maize (Zea mays L.) double cropping systems in the North China Plain (NCP). A two-year experiment with four irrigation levels based on crop growth stages was used to calibrate and validate RZWQM2, a hybrid model that combines the Root Zone Water Quality Model (RZWQM) and DSSAT4.0. The calibrated model was then used to investigate various irrigation strategies for high yield and water use efficiency (WUE) using weather data from 1961 to 1999. The model simulated soil moisture, crop yield, above-ground biomass and WUE in responses to irrigation schedules well, with root mean square errors (RMSEs) of 0.029 cm³ cm⁻³, 0.59 Mg ha⁻¹, 2.05 Mg ha⁻¹, and 0.19 kg m⁻³, respectively, for wheat; and 0.027 cm³ cm⁻³, 0.71 Mg ha⁻¹, 1.51 Mg ha⁻¹ and 0.35 kg m⁻³, respectively, for maize. WUE increased with the amount of irrigation applied during the dry growing season of 2001-2002, but was less sensitive to irrigation during the wet season of 2002-2003. Long-term simulation using weather data from 1961 to 1999 showed that initial soil water at planting was adequate (at 82% of crop available water) for wheat establishment due to the high rainfall during the previous maize season. Preseason irrigation for wheat commonly practiced by local farmers should be postponed to the most sensitive growth stage (stem extension) for higher yield and WUE in the area. Preseason irrigation for maize is needed in 40% of the years. With limited irrigation available (100, 150, 200, or 250 mm per year), 80% of the water allocated to the critical wheat growth stages and 20% applied at maize planting achieved the highest WUE and the least water drainage overall for the two crops.     

Classical metapopulation theory as a useful paradigm for the conservation of an endangered amphibian

Classical metapopulation theory (CMT) has proven an attractive paradigm for ecologists concerned with the conservation of aquatic-breeding amphibians, given its apparent fit with the population dynamics of these animals, and the opportunities the concept provides to assess alternate management options. Nevertheless, several authors have cautioned against uncritical application of this paradigm. We assessed the application of CMT to the conservation of the endangered growling grass frog (Litoria raniformis) in the urbanising landscapes of Melbourne, Victoria, Australia. Support for five predictions developed from the basic tenets of CMT was assessed using a multi-year occupancy and mark–recapture data-set. There was congruence between all five predictions and data. Wetland occupancy was strongly influenced by the proximity of neighbouring populations (‘connectivity’), but the estimated rate of dispersal between wetlands was low. Wetland occupancy was also temporally dynamic, with only a weak effect of connectivity on the probability of extinction, but a strong positive influence of connectivity on the probability of colonisation. Our work confirms that CMT provides a useful model of the dynamics of L. raniformis in urbanising landscapes, and justifies the application of the paradigm to conservation planning for this species. We argue that CMT may prove relevant to numerous aquatic-breeding amphibians, and encourage assessment of the application of CMT to the conservation of these animals.