RAJA RAM KHANAL1, FOLKARD ASCH2, MATHIAS BECKER2
1University of Bonn, Agricultural Science and Resource Management in Tropics and Sub-tropics (arts), Germany
2University of Bonn, Plant Nutrition in the Tropics and Subtropics, Germany
Nepal's most important crop production system is the rice - wheat rotation cropping. Rice is the most important food crop of Nepal and is cultivated under a wide range of ecological conditions. This crop is grown from elevations of 60m asl up to 3050m altitude, which is the highest altitude in the world for rice cultivation. The average yield of rice in Nepal is [2.7]tha in Nepal. The rice-wheat crop rotation is characterised also by a more or less prominent transition period between the harvest of the wheat and the planting of the rice, that can be used to grow spring crops like mung bean, sunflower etc. The length of the transition period differs with the climatic environment and is directly related to the elevation above sea level of the production system. Proper management of this transition period leads to nutrient conservation and more efficient nutrient use of the following rice crop and in the long run increases the sustainability of the system. Such transition season crops and/or the replacement of the dry season wheat by a crop of potatoes, can result in a substantial deviation from the recommended transplanting date for rice. In those cases, both early and late planted rice can experience periods of thermal stress that may extend the duration to flowering and /or result in cold-induced spikelet sterility. In cases where, in order to fit a transition crop, deviation from the normal transplanting time for rice (June and July) crop duration becomes the major agronomic parameter determining the agronomic fit of a rice genotype. Crop duration determines the ability of the crop to escape from climatic stresses, for example thermal stresses occurring during the cold or hot season in semi-arid and mountain environments. The identification of rice genotypes adapted to different planting times is crucial to enhance the productivity of rice based systems within the merging modified cropping calendars. This study investigates phenological and yield component responses of some 30 rice genotypes to staggered fortnightly seeding dates to ultimately develop a risk assessment tools for cropping calendar adaptation.
Keywords: Cropping calendar development, Nepal, risk assessment, sterility, temperature responses