Modifications in rice plant development induced by aerobic soil conditions

(1)

Modifications in rice plant development induced

by aerobic soil conditions

Increasing water cost and scarcity drive rice farmers in many regions to switch to less water-consuming systems. For

maximized water savings, aerobic crop management with direct seeding and regular short irrigations to achieve

saturated soil water content can be done. Current research aims to usher this transition without sacrificing the yield.

Benoit Clerget, Crisanta Bueno, Edu Foronda, Elmer Duque, Allene Macabuhay,

Heathel Loren Layaoen, and Abigail Domingo

CIRAD, UMR AGAP, F-34398 Montpellier, France

International Rice Research Institute, DAPO Box 7777, Metro Manila 1301, Philippines

Email address: b.clerget@irri.org

Approaches and methods

Identical rice varieties were sown and grown simultaneously under aerobic and flooded soil environments in the field and in the greenhouse. Crop growth and development in all the experiments were monitored weekly.

1. Comparison of field crops under best management

It was thus hypothesized that the modification of the rate of plant development was a pivotal effect in the plant reaction to the aerobic environment that induced, through a chain of aftereffects, a large part of the observed differences in plant architecture and efficiency.

In pots with low plant density, aerobic conditions still yielded an earlier but little pronounced decline in the rate of leaf appearance.

Conclusions

In aerobic rice crops we observed that the rate of

development drops earlier and much lower in aerobic than in flooded crops. We hypothesize that these changes are central in the process of plant adaptation to environmental

differences; this justifies the need to study their patterns and mechanism. Such knowledge will be useful in fine-tuning aerobic crop management and in breeding specific varieties to finally reduce the yield gap between aerobic and flooded rice crops.

P352

Flooded Aerobic

Variety

Location IRRI, Los Baños, PhilippinesNSICRc222 Crop establishment Irrigation Nitrogen (kg/ha) Lowland farm Transplanting, 20x20 cm Continuous flooding 120 Upland farm Direct seeding, 40-60 kg/ha Soil water saturation

160

Watering Year Grain Yield (g.m-2₎ Shoot Biomass (g.m-2₎ Flooded Aerobic 2011 2012 2011 2012 832 730 602 549 1606 1492 1188 1237 Grain yield and shoot biomass were reduced by 1 to 2 t ha-1

and 2 to 4 t ha-1_{, respectively, in aerobic plots.}

Plant height and leaf area index (LAI) were lower, while the number of tillers produced per area was higher under aerobic conditions, in agreement with reports from previous authors.

The decline of the leaf appearance rate was earlier and more pronounced in aerobic crops (after leaf 8) than in flooded crops (after leaf 12), resulting in fewer leaves from the main stem of aerobic plants. Also, the individual leaf areas of aerobic plants were lower from leaf 6 onwards, which explained the lower LAI in spite of the higher number of tillers.

2. Effect of aerobic conditions on the rate of plant development

3. Effect of transplanting on the rate of plant development

In the field with plants at equal densities, the development of transplanted plants was slower while they were in the nursery and after transplanting. A subsequent recovery process, meanwhile, resulted in the production of 1.5 additional leaves: the transplanting method was the main reason for the differences between rates of development.

Field

Variety NSICRc222 Transplanted / dry direct seeding / wet direct seeding at 20 x 20 cm

Continuously flooded from 3rd week

Reduced leaf area per tiller

Modified leaf profile High plant density Insufficiently reduced tillering Aerobic crop

Higher LAI until PI Lower LAI after PI Lower light interception after PI Reduced plant height Consequences ? Reduced size of phytomers

Slower leaf appearance

Lesser leaves per stem Lower N content

High tiller density

Reduced sheaths Reduced internodes Lower biomass accumulation after PI Hypothetic scheme of relations between traits ? Reduced leaf area per tiller

High tiller density

Reduced sheaths Reduced internodes Lower biomass accumulation after PI Hypothetic scheme of relations between traits Reduced leaf area per tiller

High tiller density

Reduced sheaths Reduced internodes Lower biomass accumulation after PI Hypothetic scheme of relations between traits ? ?

Reference Clerget B, Bueno C, Quilty JR, Correa Jr, TQ, Sandro J. 2014. Modifications in development and growth of a dual-adapted tropical rice variety grown as either a flooded or an aerobic crop. Field Crops Res. 155: 134-143.

Plant height 0 0.2 0.4 0.6 0.8 1 0 500 1000 1500 2000 Thermal time (°Cd) P lan t heig ht (m )

Flooded 2011 Flooded 2012 Aerobic 2011 Aerobic 2012

Leaf Area Index

0 2 4 6 8 0 500 1000 1500 2000 Thermal time (°Cd) Lea f ar ea ind e x Tiller density 0 400 800 1200 0 500 1000 1500 2000 Thermal time (°Cd) T ill e rs d e n s ity (n o .m -2) Leaf appearance 0 5 10 15 20 0 500 1000 1500 2000 Thermal time (°Cd) N u m b e r o f leav es

Flooded 2011 Flooded 2012 Aerobic 2011 Aerobic 2012

Leaf area 0 10 20 30 40 50 60 0 5 10 15 Leaf rank L e af a rea ( cm ²) Leaf appearance 0 5 10 15 0 500 1000 1500 Thermal time (°Cd) A p pe ar e d le av es

Transplanted Dry DS Wet DS

12 8

Transplanting Variety NSICRc222 direct seeded

Floodedor Aerobic Leaf appearance 0 5 10 15 20 0 500 1000 1500 2000 Thermal time (°Cd) Nu m b er o f ap p eared lea v es Flooded Aerobic 8 12 Variety NSICRc222 direct seeded

Floodedor Aerobic

Variety NSICRc222 direct seeded Floodedor Aerobic Leaf appearance 0 5 10 15 20 0 500 1000 1500 2000 Thermal time (°Cd) Nu m b er o f ap p eared lea v es Flooded Aerobic 8 12