Long-Term Continuous Cropping Experiments (LTCCE)
The long term continuous cropping experiment (LTCCE) at IRRI is the world's longest running experiment on triple rice cropping system. It was started in May 1962 to determine the maximum productivity that a one hectare land can provide. From 1963 to 1968, 13 rice crops were grown in the experimental area at an average cropping intensity of 2.5 crops per year. It was turned into a continuous triple-crop rice system in 1968 when short-duration, high-yielding varieties became available. From 1968 to the present three rice crops were grown per year except in 1991, 1993, and 1994 when only two crops were grown per year due to infrastructure rehabilitation. The three crop-growing seasons are (i) dry season (DS; January-April), (ii) early wet season (EWS; May-August), and (iii) late wet season (LWS; September-December). The time interval between harvest and transplanting is about 14 days.
The initial objective of the LTCCE to achieve maximum yields and productivity has evolved into looking at sustainability of crop intensification and how the system is affected by climate change over time. Now, it serves as a field laboratory for providing answers to potential challenges that farmers engaged in such intensive cropping systems will encounter in the future.
Determine the effect of continuous triple rice cropping on crop productivity and sustainability of intensive rice cropping systems.
Assess the effect of continuous triple rice cropping on soil physical and chemical parameters, and its effect on indigenous nutrient supplying capacity.
Assess the long term trends in the gap between actual attained and potential yields as determined by the germplasm and climate conditions.
Determine the trends in N response and N use efficiencies as affected by variety, season, and changing climate.
Split-split plot design with four N rates as the main plot factor and three to six varieties as subplot factor, with four replicate plots.
NITROGEN MANAGEMENT depends on the cropping seasons
26 kg P/ha and 40 kg K/ha are broadcasted and incorporated 2 days before transplanting in each season. 5 kg Zn/ha as zinc sulfate is broadcast and incorporated with the P and K before dry season crop.
14-day-old dapog seedlings are transplanted with 3-5 seedlings per hill at 20 cm x 20 cm spacing.
Pest and disease control:
Control measures include molluscide to control snail and herbicide for weeds after transplanting. Any additional pesticides are applied as needed.
Soil sampling (0-20 cm) after land preparation, before basal fertilization (every 3 years for archiving);
Bulk density determination (0-20 cm) as needed;
NPK concentration in irrigation water source at three times in the season (before transplanting, about 25 DAT, and about 50 DAT when budget is available);
Grain and straw yield at maturity for 6 varieties: 96 plots; and
Yield components and grain and straw N concentration from 12 hills at maturity (96 plots). Yield components include tiller number, panicle number, plant height, 1000 grain weight, harvest index, unfilled spikelet weight, % filled grain, grain weight, and straw weight. [N concentration is not routinely determined for unfilled spikelets.