Influence of agricultural practices and climate changes in Portuguese rice production

Abstract

Rice is one of the most important food crops in the world and the staple for more than half of the global population. Portugal is the first rice consumer, per capita, in Europe and the fourth producer (6 t ha-1), contributing to the 5.3% of the total European production. Rice cultivation in Portugal is intensive and is mostly located in the central and southern regions (Mondego, Tagus and Sado Valleys). The cultivation in Europe is mainly by flooding to control soil temperature, weeds and pests. The water content of soils can vary considerably, depending on climatic conditions, soil type and agricultural practices. In Portugal, rice straw is returned to the field after harvest, partially is burnt and partly is incorporated preceding the rice cultivation. Straw incorporation in soil in the non-rice-growing season can result in lower methane emission in the following rice-growing season than does the incorporation just before rice cultivation. The anaerobic conditions in flooded soils influence nitrogen (N) fertilizers dynamics, particularly the redox potential and soil pH. Rice roots absorb nitrate (NO3 –) or ammonium (NH4 +) from soil using a variety of transporters, but NH4 + is the preferential form in waterlogged soils. Nitrogen use efficiency is generally low (20-35%). In 2011, we evaluated the soil and floodwater N and pH dynamics, and the rice response to the actual agricultural practices in an open field at Salvaterra de Magos (central Portugal), and in open top chambers with increased atmospheric carbon dioxide concentration [CO2] and temperature