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BACKGROUND
The rice-upland crop rotation experiment started at IRRI in 1993 to look into the sustainability of double cropping systems where rice is alternately grown with an upland crop (maize), creating an alternately aerobic–anaerobic soil conditions for maize-rice, and continuously anaerobic for rice-rice systems. There are two cropping seasons (i) dry season (January-April) and (ii) wet season (June-October). Soil analyses indicated a strong effect of crop rotation on total soil carbon and nitrogen. Consequently, it evolved into looking at sustainability these double cropping systems, with and without tillage, in the presence and absence of crop residues. Now, it serves as a field laboratory for providing answers to the potential challenges that these systems may create in the long term.
Determine the effect of crop diversification from lowland flooded rice to an upland crop on soil properties and measures of soil quality including soil organic matter, mineralization, and carbon balances
Assess the effects of cropping system and N fertilization on yield and nutrient balances
Assess the effects of tillage on yield and its interaction with the cropping system and N fertilization
Assess the effects of straw management on yield and its interaction with the cropping system and N fertilization
EXPERIMENT DESIGN
Year started: 1993 WS
Experimental Design: Split-split plot
Number of crops/seasons: 2
Seasons: Dry and wet season
Main plot: Cropping pattern
R-R (Rice-Rice)
R-M (Rice-Maize)
In dry season, half of the plots are sown with maize, while the other half is transplanted with rice.
Subplot factor: N fertilizer (1993 - 2011), Tillage (2012 - present)
1993 - 2005: N1 - 0 N Control; N2 - Low N; N3 - high N input (13 years)
2006 - 2011: N1- 0 N Control; N2 - SSNM fixed-time N management; N3 - high N input (6 years)
2012 - present: N1 - SSNM (historically no N plots), conventional tillage; N2 - SSNM (historically N fertilized plots), conventional tillage; N3 - SSNM (historically N fertilized plots), no tillage (8 years)
In wet season, all plots are transplanted rice, with conventional tillage
Subplot factor: N fertilizer (1993 - present)
1993 - 2005: N1 - 0 N Control; N2 - Low N; N3 - high N input (13 years)
2006 - 2011: N1 - 0 N Control; N2 - SSNM fixed-time N management; N3 - high N input (6 years)
2012 – present: N1 - 0 N Control; N2 - SSNM (R-M plots with higher N); N3 - SSNM (R-M plots with higher N) (8 years)
In both DS and WS,
Sub-subplot factor: Straw management (1993 - present)
1993 - 2000: Sub-subplot is timing of residue incorporation (7 years), all plots were with residue incorporation
2001 - present: Sub-subplot is residue incorporation (17 years)
CROP MANAGEMENT
Crop establishment
Dry season rice: 14-day-old dapog seedlings of IRRI 146 (NSIC Rc158) are transplanted with 2-3 seedlings per hill at 30 cm row spacing and 13.5 cm spacing within row.
Dry season maize: Sown every 18 cm on ridges which are spaced 75 cm apart. Available hybrid variety is sown on about 15-cm high ridges.
Wet season rice: 14-day-old dapog seedlings of IRRI 146 (NSIC Rc158) are transplanted with 2-3 seedlings per hill at 20 cm row spacing and 20 cm spacing within row (20 cm x 20 cm).
Tillage and straw
All plots undergo conventional puddled land preparation in wet season because all plots are planted with rice during this season. However, during dry seasons, half of the experiment is sown with maize, and the other half is transplanted with rice. Plots with tillage are conventionally tilled i.e. dry rotovation for maize plots as soon as it is sufficiently dry; and puddled land preparation for rice plots. For -straw plots, all aboveground crop residues are removed immediately after harvest, while the crop residues remain in situ with +straw plots. The latter gets incorporated 2-3 weeks before crop establishment.
Fertilization
Dry season
P and K rates for rice plots:
40 kg P2O5 ha-1, 20 kg K2O ha-1
P and K rates for maize plots:
60 kg P2O5 ha-1 ; 30 kg K2O ha-1
Wet season
30 kg P2O5/ha; 20 kg K2O/ha;
10 kg Zn/ha
Pest and disease control
Control measures include molluscide to control snail and herbicide for weeds. Any additional pesticides are applied as needed.
MEASUREMENTS
Soil sampling (0-15 cm) after land preparation, before basal fertilization (every 3 years for archiving)
Bulk density determination (0-15 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: (48 plots)
Yield components and grain and straw N concentration from 12 hills at maturity (48 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.]
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