Luzviminda Fernandez

Structure and validation of RICEPEST, a production situation-driven, crop growth model simulating rice yield response to multiple pest injuries for tropical Asia

Abstract RICEPEST, a model simulating yield losses due to several rice pests (sheath blight, brown spot, sheath rot, bacterial leaf blight, stem borers, brown plant hopper, defoliating insects, and weeds) under a range of specific production situations of tropical Asia was developed. The model was assessed, using: (1) combined data sets generated by a series of test-experiments conducted in different sites of the Philippines, India, and China; and (2) one additional, independent, validation-experiment where a wide range of production situations and injury profiles were manipulated at a single site. Model evaluation was based on the analysis of two output variables: grain yield and relative yield loss. The paper reports results of qualitative and quantitative methods used to assess RICEPEST. Qualitative evaluation involved visual examination of graphs where deviations (simulated minus observed) are plotted against simulated values, and displaying an area of acceptance. This method showed that, in general, RICEPEST accounted well for the yield reducing effects of rice pests. Two areas for potential improvement of RICEPEST were however, identified: the simulation of damage caused by dead hearts in water-stressed environments, and the simulation of damage caused by weeds. Quantitative evaluations made use of equivalence- and χ 2 -tests. The equivalence tests rejected ( P ≤0.05) the hypothesis of difference between simulated and observed yield and relative yield loss larger than a preset tolerance in both test- and validation-experiments. Conversely, the χ 2 -tests did not reject the hypothesis of difference in categorised simulated and observed yields and relative yield losses ( P ≤0.05) in both test- and validation-experiments. RICEPEST proved to simulate adequately yield losses and can be used as a tool to set research priorities for rice crop protection in tropical Asia.

Development and evaluation of a multiple-pest, production situation specific model to simulate yield losses of rice in tropical Asia

A yield loss simulation model for rice was developed to simulate injury mechanisms due to pathogens, insects, and weeds, and the yield losses they cause in a range of production situations. The structure of the model is simple, flexible, and involves as few parameters as possible. The model consists of two linked components. The first simulates the dynamics of the rice crop, with accumulation of biomass and its daily partitioning towards leaves, stems, roots, and panicles. The second component simulates the dynamics of tillering, tiller maturation, panicle formation, and tiller death. Coupling functions representing damage mechanisms due to sheath blight, stem borers, and weeds were developed and parameterized from published and experimental data. Each of these injuries corresponds to a set of damage mechanisms, some of which are specific to the injury considered, while others are common to several injuries. The parameters required to simulate attainable growth and attainable yield were determined, using specific field experiments, under three different production situations representing those commonly occurring in the Philippines and in Vietnam. Yield loss simulations due to the different injuries, considered alone or in combination, were tested under these different production situations. The model accurately simulated attainable rice growth and development, and adequately accounted for the yield-reducing effects of the different injury mechanisms considered. Results from sensitivity analyses conducted at varying levels of injuries are discussed. This model can be used as a tool to set research priorities for novel plant protection strategies for rice in tropical Asia.

Do abiotic factors cause a gradual yield decline under continuous aerobic rice cultivation? A pot experiment with affected field soils

Abstract Aerobic rice is a water-saving technology in which rice grows in non-puddled and non-saturated (aerobic) soil without ponded water. A gradual decline in rice yield was found in field plots at the farm of the International Rice Research Institute, Los Baños, Philippines, where rice has been cultivated continuously for 10 cropping seasons under aerobic rice conditions. We investigated whether abiotic soil factors lead to the observed yield decline. An aerobic rice pot experiment was conducted using field soils from flooded rice plots and from the 10-season-long aerobic rice cultivated plots (referred to as 1st-season and 11th-season aerobic rice, respectively). Subtreatments consisted of soil sterilization by oven heating (at 95°C or higher for 24 h) and a control treatment. The above-ground biomass of 1st-season aerobic rice was significantly greater than that of 11th-season aerobic rice in both the oven-heating and control treatments. Oven heating increased soil N availability and above-ground biomass accumulation over the control in both 1st-season and 11th-season aerobic rice, but the above-ground biomass in the oven-heated 11th-season aerobic rice was still significantly lower than that of the oven-heated and even the untreated (control) 1st-season aerobic rice. These results suggest that abiotic factors contribute to the gradual yield decline observed in the field plots.