ALBERT

Notes: Competition between rice (Oryza sativa) and Echinochloa crus-galli (L.) Beauv. (barnyard-grass or cockspur) was studied experimentally in the field in Sri Lanka. By growing rice in bags sunk in the paddy soil such.that the roots of the plants were either separated from or free to mingle with those of neighbouring weeds, or by growing rice in the same bags but in the absence of weeds, it was possible to calculate the relative importance of interference below ground (root competition) and above ground (shoot competition). Three rice varieties with different above-ground morphology were inhibited to different extents by E. crus-galli but in each case root competition was more important than shoot competition. In the variety that was most sensitive to root competition, Bg 400–1, inhibition of total growth due to root competition increased with increasing weed density.When grown in monocultures in pots in the field, the two species exhibited similar growth rates whether or not the soil was fertilized, but in 1:1 mixtures growth of E. crus-galli was greater, particularly if fertilizer was added, as this promoted the growth of the weed, while having no effect on the rice. In mixture, relative yield totals were close to 1.0, with the relative yield of E. crus-galli being consistently greater than 0.5, particularly with added nutrients, while the relative yield of rice was always less than 0.5. The relative crowding coefficient for rice with respect to E. crus-galli (Keb), when based on total plant dry weight, was lower in fertilized than in non-fertilized soil, falling in the former case from 0.4 to 0.2 during the experiments Krootrb, based on root dry weight, decreased with increasing soil depth and was lower in fertilized than in non-fertilized soil, most notably after 62 days of growth, when root dry weight was at its maximum.It is concluded that inhibition of root growth of rice, leading to a reduced ability to obtain resources from the soil, was the major factor contributing to the decline in the growth of rice in the presence of E. crus-galli. Croissance racinaire et importance relative de la compétition racinaire et aérienne dans les interactions entre le riz (Oryza sativa) et le panic (Echinochloa crus-galli)La competition entre le riz (Oryza sativa) et le panic (Echinochloa crus-galli) a étéétudiée dans une expérimentation de plein champ au Sri Lanka. En cultivant du riz dans des sachets immergés dans la riziére de telle façon que ses racines soient soil séparées, soil libres de se mé1anger avec celles des adventices voisines, ou en cultivant du riz dans des sachets analogues mais en 1'absence de mauvaises herbes, il est possible de calculer 1'importance relative de 1'interférence sous le sol (compétition racinaire) et de celle au dessus du sol (compétitionaérienne). 3 variétés de riz ayant une morphologie aérienne différente ont été inhibées par le panic à des niveaux différents mais chaque fois la compétition racinaire a été plus importante que l'aérienne. Chez la variété la plus sensible à la compétition racinaire, Bg 400–1, le ralentissement de la croissance totale due à la compétition racinaire augmenta avec l'augmentation de la densité de mauvaises herbes.Quand elles sont cultivées en pots dans les champs, les deux espèces ont des taux de croissance similaires que le sol soit ou non fertilisé, mais dans un mélange 1/1 la croissance du panic est plus forte surtout si l'on ajoute de l'engrais puisque celui-ci favorise la croissance de l'adventice sans avoir d'effet sur le riz. En mélange, le total des poids relatifs était très proche de 1, avec un poids relatif de panic conséquemment plus grand que 0,5, surtout dans le cas d'adjonction d'engrais, tandis que celui du riz était toujours inférieur à 0,5. Le coefficient de tassement relatif du riz en regard du panic (Krb), basé sur le poids sec de la plante entière était plus faible dans les sols fertilisés que dans les autres, tombant de 0,4 à 0,2 pendant l'expérimentation. KracinCrb, basé sur le poids sec de racine, diminue avec l'augmentation de la profondeur du sol et est plus bas dans les sols fertilisés que dans les autres, surtout après 62 jours de croissance quand le poids sec de racine est à son maximum. Il est conclu que le ralentissement de la croissance des racines de riz, aboutissant à une capacité moindre à prélever les ressources du sol, était le facteur principale de la réduction de la croissance du riz en présence de panic. Wurzelwachstum von und Wurzel- sowie Sproßkonkurrenz zwischen Reis (Oryza sativaj und Echinochloa crus-galliIn Freilandversuchen in Sri Lanka zur Wurzelund Sproßkonkurrenz zwischen Reis (Oryza sativa L.) und Hühnerhirse (Echinochloa crus-galli (L.) Beauv.) wurde Reis so in Beuteln gepflanzt, daß seine Wurzeln sich entweder getrennt oder mit denen des Unkrauts zusammen wachsend entwickeln konnten. Andere Parzellen blieben unkrautfrei. E. crus-galli konkurrierte mit 3 Reissorten von unterschiedlicher Sproßmorphologie verschieden stark, doch die Wurzelkonkurrenz war immer bedeutender als die Sproßkonkurrenz. Bei der gegen Wurzelkonkurrenz empfindlichsten Sorte “Bg 400–1” war die Gesamthemmung auf die mit der Unkrautdichte zunehmende Wurzelkonkurrenz zurückzuführen. In Monokultur hatten beide Arten unabhängig von der Düngung ähnliche Wachstumsraten, aber in l:l-Mischkulturwuchs E. crus-galli stärker, besonders bei Düngung, die auf den Reis wirkungslos blieb. In Mischkultur lag der relative Gesamtertrag nahe 1,0, wobei der Ertrag von E. crus-galli stets über 0,5, der des Reises jedoch immer unter 0,5 lag. Für die Wechselbeziehung zwischen Reis und E. crus-galli auf die Gesamttrockenmasse wurde ein ‘crowding coefficient’ (Krb) für Reis berechnet, der mit Düngung kleiner war als ohne. Krb nahm während des Versuchs von 0,4 auf 0,2 ab. Der auf die Wurzeltrockenmasse bezogene ‘crowding coefficient’ (Krootrb) nahm mit zunehmender Bodentiefe ab. Krootrb war niedriger in gedüngtem verglichen mit ungedüngtem Boden. Dieser Unterschied war nach 62 Tagen Wachstum besonders deutlich, als die Wurzeltrockenmasse ein Maximum erreichte. Die Hemmung des Wurzelwachstums des Reises wurde als wichtiger Faktor für seine Wachtum-shemmung in der Gegenwart von E. crus-galli angesehen, weil sie die Fähigkeit des Reises zur Nährstoffaufnahme aus dem Boden verringert.

Notes: Abstract The beneficial effect of organic matter on soil aggregate stability is well documented. Alley cropping has been suggested as a possible alternative to maintain soil organic matter content in cropping systems without fallowing the land. The objective of this study was to asses the effect of alley cropping on dry and wet soil aggregate stability on land degraded by shifting cultivation. The aggregate size distribution by dry sieving, aggregate stability by wet sieving, soil organic Carbon content and soil bulk density were measured following two and three years of alley cropping with Gliricedia (Gliricidia sepium) and Pigeon pea (Cajanas cajan) in a tropical Rhodustalf. Alley cropping increased the mean aggregate diameter and water stability of soil aggregates. The mean aggregate diameter obtained from dry sieving increased from 1.3 mm of the control to 2.68 and 3.11 mm after three years in Pigeon pea and Gliricidia alley cropped plots, respectively. This is an indication of resistance to wind erosion in alley cropped plots. The wet aggregate stability which shows the resistance to erosion by water also increased in alley cropped plots. These increases were significant after three years of hedge row establishment. The increase in soil organic C in alley cropped plots contributed to the higher dry and wet aggregate stability, and decreased soil bulk density. The improvement was higher in plots alley cropped with Gliricidia than Pigeon pea. This study shows the importance of ally cropping in increasing aggregate stability of degraded sandy soils which in return reduce erosion by wind and water.

Notes: Abstract The rehabilitation or intensified use of Imperata grasslands will require a much better understanding of their area, distribution, and characteristics. We generated estimates of the area of Imperata grasslands in tropical Asia, and suggested a typology of Imperata grasslands that may be useful to define the pathways toward appropriate land use intensification. We conclude that the area of Imperata grasslands in Asia is about 35 million ha. This about 4% of the total land area. The countries with the largest area of Imperata grasslands are Indonesia (8.5 million ha) and India (8.0 million ha). Those with the largest proportion of their surface area covered with Imperata are Sri Lanka (23%), the Philippines (17%), and Vietnam (9%). Laos, Thailand, Myanmar, and Bangladesh evidently all have similar proportions of their land area infested with Imperata (about 3 to 4%). Malaysia (〈 1%), Cambodia (1%), and the southern part of China (2%) have but a minor proportion of their total land area in Imperata. The species was found widely distributed on the full range of soil orders. It occupied both fertile (e.g. some of the Inceptisols and Andisols) and infertile soils (Ultisols and Oxisols) across a wide range of climates and elevations. Imperata lands fall into four mapping scale-related categories: Mega-grasslands, itmacro-grasslands, meso-grasslands, and micro-grasslands. The mega-grasslands are often referred to as ‘sheet Imperata’. They are the large contiguous areas of Imperata that would appear on small-scale maps of say 1:1,000,000. We propose that this basic typology be supplemented with a number of additional components that have a key influence on intensification pathways: land quality, market access, and the source of power for tillage. The typology was applied in a case study of Indonesian villages in the vicinity of Imperata grasslands. We propose an international initiative to map and derive a more complete and uniform picture of the area of the Imperata grasslands. This should include selected studies to understand conditions at the local level. These are critical to build the appreciation of change agents for the indigenous systems of resource exploitation, and how they relate to local needs, values and constraints.