The System of Rice Intensification (SRI)

Some interesting data and observationson the contributions of soil biota for rice

crop performanceIntended to prompt thinking and research

Importance of Soil Aeration

• Stimulate aerobic soil organisms since they are critical for soil fertility• Nitrogen fixation - nitrifiers• Phosphorus solubilization – phosphobacteria• Mycorrhyzal fungi – access water, P, etc.• Nutrient cycling – protozoa, nematodes• Induced systemic resistance (ISR)

• Very little evaluation of their contributions

Soil-aerating hand weeder in Sri Lanka costing <$10

Effects of Active Soil Aeration using Mechanical WeederMechanical Weedings

(N) Yield (t ha-1)

MADAGASCAR: 1997-98 main season -- Ambatovaky (N=76)

None 2 5.97One 8 7.72Two 27 7.37

Three 24 9.12Four 15 11.77

NEPAL: 2006 monsoon season – Morang district (N=412)

One 32 5.16(3.6 – 7.6)

Two 366 5.87(3.5 – 11.0)

Three 14 7.87(5.85 – 10.4)

Why Is ‘Weeding’ So Important?

Not just to control weeds; also benefit from the green-manure effect of weeds when they decompose in the soil (keep nutrients)

Also, promotion of beneficial soil organisms, both bacteria and fungi (mycorrhizae)

No flooding should promote benefits of latterWe are learning that these organisms

function not only in the soil -- but also IN the plant

• As symbiotic endophytes in the ROOTS• Also as endophytes in the LEAVES• Even as endophytes in the SEED COAT!

Microbial populations in rice rhizosphere

Tamil Nadu Agricultural University research

Microorganisms

Conventional

SRI

Total bacteria 88 x 106 105 x 106

Azospirillum 8 x 105 31 x 105

Azotobacter 39 x 103 66 x 103

Phosphobacteria

33 x 103 59 x 103

T. M. Thiyagarajan, WRRC presentation, Tsukuba, Japan, 2004

Total bacteria Total diazotrophs

Microbial populations in rhizosphere soil in rice crop under different management at active tillering, panicle initiation and flowering (SRI = yellow; conventional = red)

[units are √ transformed values of population/gram of dry soil] (IPB data)

Phosphobacteria\

Azotobacter

Dehydrogenase activity (μg TPF) Urease activity (μg NH4-N))

Microbial activities in rhizosphere soil in rice crop under different management (SRI = yellow; conventional = red) at active tillering, panicle initiation and flowering

stages [units are √ transformed values of population/gram of dry soil per 24 h]

Acid phosphate activity (μg p-Nitrophenol) \Nitrogenase activity (nano mol C2H4)

Total microbes and numbers of beneficial microbes (CFU g-1) under conventional and SRI cultivation methods, Tanjung Sari,

Bogor, Indonesia,Feb-Aug 2009 (Iswandi et al., 2009)

Cultivation method and fertilization

Total microbes

(x105)

Azoto-bacter(x103)

Azospi-rillum(x103)

P-solubilizing bacteria

(x104)

Conventional crop mgmt with NPK

2.3a 1.9a 0.9a 3.3a

Inorganic SRI (NPK fertilizer)

2.7a 2.2a 1.7ab 4.0a

Organic SRI (compost)

3.8b 3.7b 2.8bc 5.9b

Inorganic SRI + biofertilizer

4.8c 4.4b 3.3c 6.4b

ENDOPHYTIC AZOSPIRILLUM, TI LLERING, AND RICE YIELDS WITH CULTIVATION PRACTICES AND NUTRIENT AMENDMENTS Replicated trials at Anjomakely, Madagascar, 2001 (Andriankaja, 2002)

Azospirillum No. of CLAY SOIL in roots

(103/mg) tillers/

plant Yield (t/ha)

Traditional cultivation, no amendments

65 17 1.8

SRI cultivation, with no amendments

1,100 45 6.1

SRI cultivation, with NPK amendments

450 68 9.0

SRI cultivation, with compost

1,400 78 10.5

LOAM SOIL SRI cultivation with no amendments

75 32 2.1

SRI cultivation, with compost

2,000 47 6.6

Endophytic-Symbiotic Microbes Contribute to the Productivity of Rice Plants -- and

Not Only in Rhizosphere

We find there are beneficial effects of microorganisms – both bacteria and fungi – in the leaves (phyllosphere) and in the seeds

(affecting germination and early growth)

Ascending Migration of Endophytic Rhizobia, from Roots and Leaves, inside Rice Plants and Assessment of Benefits to Rice

Growth Physiology Feng Chi et al.,Applied and Envir. Microbiology 71 (2005), 7271-7278

Rhizo-bium test strain

Total plant root

volume/pot (cm3)

Shoot dry weight/ pot (g)

Net photo-synthetic

rate (μmol-2 s-1)

Water utilization efficiency

Area (cm2) of flag leaf

Grain yield/ pot (g)

Ac-ORS571 210 ± 36A 63 ± 2A 16.42 ± 1.39A 3.62 ± 0.17BC 17.64 ± 4.94ABC 86 ± 5A

SM-1021 180 ± 26A 67 ± 5A 14.99 ± 1.64B 4.02 ± 0.19AB 20.03 ± 3.92A 86 ± 4A

SM-1002 168 ± 8AB 52 ± 4BC 13.70 ± 0.73B 4.15 ± 0.32A 19.58 ± 4.47AB 61 ± 4B

R1-2370 175 ± 23A 61 ± 8AB 13.85 ± 0.38B 3.36 ± 0.41C 18.98 ± 4.49AB 64 ± 9B

Mh-93 193 ± 16A 67 ± 4A 13.86 ± 0.76B 3.18 ± 0.25CD 16.79 ± 3.43BC 77 ± 5A

Control 130 ± 10B 47 ± 6C 10.23 ± 1.03C 2.77 ± 0.69D 15.24 ± 4.0C 51 ± 4C

Data are based on the average linear root and shoot growth of three symbiotic (dashed line) and three nonsymbiotic (solid line) plants.

Arrows indicate the times when root hair development started.

Ratio of root and shoot growth in symbiotic and nonsymbiotic rice plants -- symbiotic plant seeds were inoculated with Fusarium culmorum

Russell J. Rodriguez et al., ‘Symbiotic regulation of plant growth, development and reproduction,’

Communicative and Integrative Biology, 2:3 (2009).

Growth of nonsymbiotic (on left) and symbiotic (on right) rice seedlings. On growth of endophyte (F. culmorum) and plant

inoculation procedures, see Rodriguez et al., Communicative and Integrative Biology, 2:3 (2009).

Research is just beginning in these areas – to know what are the positive (and negative) plant-microbial interactions occurring in the phyllosphere and in

seedsMuch more is known, but still not enough, about interactions in the

rhizosphere

As we learn more about what is occurring, we can begin to learn better

what can be done to manage and improve these interactions

in, on and around crop plants

[See research findings reported in A. Varma et al., Plant Surface Microbiology, Springer Verlag, 2007]