Thesis Abstract of AGS Students

Grain yield assessment of quality protien maize in different environments using a modelling approach

Fan Xingming (1995)

Maize is the second most important crop in Yunnan province. Quality Protein Maize (QPM) varieties were introduced to Yunnan in 1988 by the International Maize Wheat Improvement Center (CIMMYT) through its International Maize Testing Program. So far, several QPM varieties have been released, and have been quickly accepted by farmers, covering more than 667 ha in 1993.

The quantity of farmers' nitrogen applications is different from region to region in Yunnan, which could affect economic returns of QPM, and the relationship between nitrogen quantity and grain yield needs to be examined.

A structured survey was conducted in Wenshan, Simao, and Lincang, where QPM has been released, and a nitrogen* variety experiment was conducted in the Research Station of Yunnan Academy of Agriculture Science (25 ^oN, Lat., 109 ^oE Long., 1900 msl.). There were five nitrogen levels, i.e. 100 (N1), 145 (N2), 185 (N3), 230 (N4), and 270 (N5) kg ha-1. Three maize varieties were used, i.e., Across 8763 (V1, QPM), Poza Rica 8763 (V2, QPM), and normal maize Mobei 1 (V3). Both

the survey and the experiment suggested that farmers can obtain higher economic returns by growing the QPM cultivars than growing normal variety Mobei 1, and the QPM cultivars are com- patible with the current farming system in Yunnan. QPM responded to nitrogen applications up to 270 kg ha-1 in Kunming. But marginal analysis showed that if the amount of nitrogen applications is in the range of 100-230 kg ha-1, the marginal rate of return is greater than acceptable rate of return in Kunming.

Traditional agricultural research result is recognized as site specific, slow, and expensive. One alternative to solve this problem is to use modeling approach. In order to simulate the ffects of management practice on growth and development of different maize cultivars by using the CERES-Maize model in Northern Thailand, one varieties* planting dates experiment was conducted in the Research Station of the Multiple Cropping Center, Faculty of Agriculture, Chiang Mai University (18o47' Lat., 99o57' Long., 300 msl). The experiment was conducted to generate data set for use in genetic coefficients determination. Three maize cultivars were used, Across 8763 (QPM), Poza Rica 8763 (QPM), and Suwan 1. The Genotype Coefficients Calculator (GENCAL) was used to determine a set of genetic coefficients for the three cultivars. Effects of planting dates on growth and development of different maize cultivars was satisfactorily simulated by the CERES-Maize model. This set of genetic coefficients was then used to simulate effects of management practices in Yunnan. The CERES-Maize model demonstrated acceptable ability to simulate phenology events, e.g., silking, and physiological maturity dates, but the model overestimated grain yields.

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