Nitrogen fixation in rice based cropping systems. Rice

Transcription

1 Nitrogen fixation in rice based cropping systems Rice Stable food for more than half of the world population 90% is produced in Asia Production maintained at ~ 2t ha -1 without fertilizer input (paddy) - flooding water contains nutrients - leaching small - erosion small - denitrification small (can be high at the beginning of the season) -N 2 fixation by cyano- and heterotrophic bacteria R. Faidutti/FAO photo R. Faidutti/FAO photo Rice terraces in Indonesia Farmer using animal traction to plough rice fields 1

2 Free living cyanobacteria Cyanobacteria in symbiosis with Azolla Free living i soil N 2 fixers Root associated N 2 fixers (Greenland 1997) Cyanobacteria and N 2 fixation Free living Soil Cyanobacteria Water Symbiosis with Azolla Free living cyanobacteria Can be found in all soil N 2 fixation of ~ kg ha -1 recovery in following rice ~ 25% (4-6 kg) How to improve N 2 fixation by free living cyanobacteria Inoculate soil with efficient strains?? Enhance the growth of indigenous cyanobacteria - improve P-availability - increase ph - prevent predation by invertebrates 2

3 Azolla C. Van Hove, 1989 (Giller and Wilson, 1991) 3

4 a) The water fern Azolla, b) leaf with cavities and blue green alga (cyanobacteria, Anabaena Azolla), c) Anabaena Azolla. Müller-Sämann and Kotschi, Symbiosis with Azolla Azolla fern always found in symbiosis with cyanobacteria Azolla can double its weight in 2-3 days Cultivation strategies A) Monocropped before rice - one time operation - easy to use machines for incorporation - does take rice space (could have been growing rice) Incorporating of an Azolla monocrop with a power driven cultivator. (C. Van Hove, 1989). B) Intercropped among rice and incorporated periodically - does not take rice space C) Combination Rice Azolla intercrop, note the absence of weeds, China, C. Van Hove,

5 Inoculation (Introduction of plant materials) - Where the soil is dry seasonal climate - From canals, ponds - Need is ~ 2-5 t ha -1 Harvesting Azolla from irrigation canal (C. Van Hove, 1989). Inoculation of rice paddies by draining. (C. Van Hove, 1989). Inoculation of Azolla in a rice field. (C. Van Hove, 1989). Spreading Azolla with a broom made of twigs. (C. Van Hove, 1989). 5

6 N 2 -fixation Most of the N ~70-90% is derived from fixation N 2 fixation of ~20-50 kg N ha -1 N recovery N-release by decomposition only (no transfer) up to 40% N recovered 1. Season highest N recovery when incorporation N losses Azolla N ~ 0-11 % Urea N ~30 % When urea and Azolla are used in combination losses are substantially reduced (ph lowered) Incorporation of intercropped Azolla by foot-stamping after partial drainage of the field. (C. Van Hove, 1989). Common environmental constraints Temperature Lack of P and other nutrients Low ph Competition for light Salt Insects Weeds Best at: º C ~ ½ kg P ha -1 every 4 days Neutral mildly acid > 25% of full sun light < 0.3% 6

7 Transfer of Azolla from lake to vegetable garden, Senegal, (C. Van Hove, 1989). J. Dent/FAO photo Inter-row areas being prepared for Azolla inoculation Other uses: animal and human? feed Duck feed Fish pond Pick feed (C. Van Hove, 1989). Fish pond 7

8 : Inoculation of the rice field with Azolla; 2: Beating (loosening) of Azolla; 3: Incorporating (also done manually); 4: Beginning of the new cycle. Modified from Müller-Sämann and Kotschi, % (Giller and Wilson 1991) Yield increase in (China) kg ha-1. Only used on 2% of the world rice! - labour intensive - P need - insecticides - availability of fertilizers 8

9 Conclusions The following question about cultivation should be considered before Azolla is recommended to farmers: Does the cropping system allow the growing of Azolla as a monocrop or intercrop, and is water readily available? How can some Azolla be maintained during the off-season and how can it be multiplied and distributed before large-scale field cultivation? Is water rich in essential plant nutrients, especially P, to support rapid growth of Azolla? Is the water neutral to mildly acidic in ph and does it contain less than 0.3 % salt? Will it be necessary to frequently use pesticides for insect control? Will Azolla cultivation improve the economic situation of the farmer? Are the farmers trained? Upland Green Manures in Rice systems Lowland Green manure systems in low-land rice: Pre-rice GM (short period) - monocropped before the establishment of the rice crop and incorporated during land preparation (6-10 weeks) Post-rice GM (longer period) - relay established into the growing rice or, - monocropped after the rice is harvested Green manure systems in upland rice: Pre-rice GM - monocropped before the establishment of the rice crop Post-rice GM - relay established into the growing rice or, - monocropped after the rice is harvested Intercropped with rice (Garrity and Becker, 1994) 9

10 Post rice: - Astragalus sinicus - Indigofera tinctoria - Calapogonium ssp. - Crotalatria ssp. - Clitoria ternatea - Desmanthus virgatus - Macroptilium atropurpureum Pre rice: - Sesbania ssp. - Aeschynomene ssp. - Sesbania rostrata - Aeschynomene afraspera - and the less drought tolerant ssp. of - Crotalaria ssp. - Tephrosia ssp. (Giller and Wilson, 1991) Potential use of legume green manures in rainfed lowland rice Legume GM days Rice Legume GM Not enough water for rice cultivation Residual water (Modified from Pandey, 1987) 10

11 kg N/ha correspond to the average amount of N applied to low-land rice in Asia N accumulation by leguminous green manures in rice based cropping systems (Becker et al., 1995) days of growth before rice planting: N accumulation varies with: - water regime - soil fertility - inoculation with rhizobia - growth duration - species -sites Lowland rice grain yield increases over unfertilized control treatment, due to leguminous green manure incorporation (Becker et al., 1995) 11

12 (Becker et al., 1995) (Becker et al., 1995) Split application of urea - loss smaller from GM than urea 12

13 Comparison of agronomic N use efficiency by lowland rice of mineral fertilizer (split-applied urea) and green manure N, (Becker et al., 1995).. At low application rates GM most efficient At high application rates FN most efficient 200 kg N applied as GM = 100 kg N applied as FN 50 kg N applied as GM = 60 kg N applied as FN The equivalent fertilizer value of N from green manures for production of lowland flooded rice in terms of N fertilizer applied urea in two split applications (Giller, 2001, based on Becker et al., 1995) The mineral fertilizer equivalence of green manure is the the amount of split applied urea N applied in order to obtain equivalent yields. 13

14 Residual effect of legume green manures on grain yield of lowland rice, (Becker et al., 1995). Green manure rice rice ~ 20%+ - Input of GM and FN similar - Losses of GM-N less than FN => Residual effect Mineral fertilizer (a) (b) Green manure (Garrity and Becker, 1994) General decline in N use efficiency with increasing N application Better N use efficiency of mineral fertilizer N under irrigation (a) - drying and wetting increases mineral N losses through denitrification and leaching. Similar N use efficiency of green manure N under irrigation and rainfed conditions(b) - green manure N may be preferable to mineral fertilizer N under rainfed conditions 14

15 Legume green manure in rainfed lowland rice Potentials and benefits: increased rice yield 1.7 Mg ha -1 high N-accumulation 100 kg N ha -1 in days high fixation rate 80% Ndfa GM less prone to loss than mineral fertilizers 35% split application of urea 15% green manure good residual effect 20% yield increase in the following crop (GM Rice Rice) - long term effect on soil fertility (SOM) supply of N, P, K, S and micro nutrients - conserved in a biological pool with high turn over improve soil physical properties conserve NO 3- prone to loss (accumulated during dry season) improve weed control Conditions for GM adaptation - the use of GM in lowland rice production has declined dramatically over the last 30 years establishment is inexpensive - land preparation, seeds, etc. seed availability - own production but very laborious - unfavorable plant architecture - shattering of seeds - asynchronous flowering - need of scarification productivity is stable with time (years) - higher variability in rice yield when using GM than MF (figs) no alternative for more profitable crops manpower and adequate implements are available for incorporation at a favorable price! low price- and high availability of N fertilizers 15

16 Estimates of Sesbania production costs when used as pre-rice green manure Cost/ha (US$) Land preparation Plowing 35 Harrowing 35 Seed 18 Labor for seeding 1 Sesbania incorporation Slicer 1 Harrow to incorporate 18 Total if full tillage Total if zero tillage Cost/kgN Production 80 kg N/ha Production cost if full tillage 1.35 Production cost if zerro tillage (same yield?) 0,47 Cost of urea (applied in the field) (Based on Garrity & Flinn 1994) 0,32 Opportunity cost of land ignored (other cash crop) Long-term beneficial effects ignored (soil fertility) Note: At the 1995 fertilizer and crop prices a grain legume (e.g. cowpea) grown instead of a GM (e.g. Sesbania) only had to yield 200 kg grain ha for being equal beneficial. Grain legumes in rice systems Growth habits (Pandey, 1987) 16

17 Even maturing - determinate Uneven maturing - indeterminate (Pandey, 1987) Erect growth Pods mature at the same time Creeping, climbing growth Flower over a longer period Pods do not mature at the same time Choosing the right variety - before rice (Pandey, 1987) Early maturing, erect, determinate Able to stand drought during early growth stages Able to stand excess water during flowering and pod filling 17

18 Choosing the right variety - after rice (Pandey, 1987) Indeterminate, pods maturing over longer periods Medium duration Able to stand excess water during early growth Able to stand drought at flowering and pod filling Especially vigorous seedlings When to plant as relay crop (Pandey, 1987) Relay cropping: Plant cowpea in standing rice, about 10 days before the rice harvest 18

19 Preparing the land high tillage Preparing the land zero tillage (Pandey, 1987) References Becker, M., Ladha, J. K., and Ali, M. (1995). Green manure technology: Potential, usage, and limitations. A case study for lowland rice. Plant and Soil 174, Garrity, D. P., and Becker, M. (1994). Where do green manures fit in Asian farming systems? In Green manure production systems for Asian ricelands (J. K. Ladha and D. P. Garrity, eds.), pp IRRI, Los Banos, Philippines. Garrity, D. P., and Flinn, J. C. (1994). Prerice green manure production in rainfed environments: a simulation model. In Green manure production systems for Asian ricelands (J. K. Ladha and D. P. Garrity, eds.), pp IRRI, Los Banos, Philippines. Giller, K. E. (2001). Nitrogen fixation in tropical cropping systems, 2nd/Ed. CABI Publishing, Wallingford. Giller, K. E., and Wilson, K. J. (1991). Nitrogen fixation in tropical cropping systems, 1st/Ed. CAB International, Wallingford. Greenland, D. J. (1997). The sustainability of rice farming, CAB International, Wallingford. Müller-Sämann, K. M., and Kotschi, J. (1994). Sustaining Growth. Soil fertility management in tropical smallholdings, Magraf Verlag, Viekersheim, Germany. Pandey, R. K., ed. (1987). A farmers primer on growing cowpea on riceland,. IRRI, IITA, Los Banos, Philippines. Van Hove, C. (1989). Azolla and its Multiple Uses with Emphasis on Africa., FAO, Rome. 19