Description of the subject. Weed pressure is a main biotic constraint in tropical agriculture. Cover crop mixtures have increased in popularity to limit weed growth through competition for resources, but the relationship between cover crop diversity and weed suppression is still under debate. Objectives. This study aimed to assess the impact of increasing cover crop diversity (one to four species) on weed control during two growing seasons (tropical summer and winter) in Reunion Island. Method. Weed control was expressed regarding ground cover by weeds and weed aboveground dry mass in the mixtures during four months of growth and its response to cover crop traits was tested using structural equation models. Results. While cover crops reduced weed ground cover and dry mass by 60% and 68% on average in summer and winter, respectively, a higher number of cover crop species within a mixture did not increase mean weed control. Nonetheless, weed control was influenced by the mixture composition and improved when including Guizotia abyssinica. Additionally, cover crop traits explaining weed control differed between growing seasons. In summer, weed control was mainly explained by the final cover crop aboveground biomass and leaf area (depletion strategy). In contrast, weed control was mainly explained by the cover crop rate of increase in ground cover (obstruction strategy) in winter. Conclusions. Using traits to characterize cover crop mixture enables us to identify mixtures of species and traits adapted to different growing conditions. Our study suggests that particular attention on species identity rather than diversity should be paid in mixture to improve weed control in tropical conditions.

Cover crops have a high potential to manage weeds through competition for shared resources in tropical agrosystems. Assessing the abilities of a large number of different plant species to compete with weeds requires experiments in different pedo-climatic environments. Our study was based on a set of 10 trials including 46 species of cover crops performed from 2016 to 2018 in three sites in Reunion Island. Our aim was to identify and measure plant traits of cover crops that maximize ground cover and weed control under a tropical climate. We characterized two traits of interest (mean ground cover and rate of increase in ground cover) and compared the family, area of origin and life cycle of the cover crops. The ability of cover crops to cover the soil increased with rate of increase in height and leaf appearance rate and tended to decrease with thermal time for emergence. Accordingly, weed control efficiency (low weed cover and dry mass) was positively correlated with ground cover, height and biomass. Using functional traits to characterize plant species enabled us to identify cover crops that could be used in tropical agrosystems as an alternative to herbicides, for instance, on sugarcane in Reunion Island.

The plant bug Moissonia importunitas (Distant‚ 1910) is reported for the first time from Reunion Island‚ where it severely damages rattle box (Crotalaria) species currently evaluated as potential service plants (particularly for soil fertility enhancement and nematode management) to be included in pineapple‚ sugarcane and fruit tree cropping systems‚ in an agroecological transition perspective. This pest was found at high population levels both in the south (Saint-Pierre) and the north (Sainte-Marie) of the island. The effects of some technical levers (e.g. choice of rattle box species‚ planting date‚ crop mixture‚ application of non-chemical plant protection products) as potential control options against this pest must be assessed before Crotalaria spp. are either promoted or ruled out as service plants in Reunionese cropping systems.

Description of the subject. Nutrient balance, windrow homogeneity and the sanitization of composts obtained from the co-composting of dairy sludge and cattle manure were investigated in Reunion at the request of the island's dairy industry, which wants both to develop the agronomic valorization of dairy sludge and to satisfy regulatory constraints on the island. Objectives. The aims of this experiment were to evaluate the feasibility of co-composting cattle manure with dairy sludge and to determine the quality of the compost produced. Method. Three heaps of manure with two doses of dairy sludge were established (on a mass basis): manure alone (T), manure 2/3 + sludge 1/3 (B1) and manure 1/2 + sludge 1/2 (B2), with a bulk density of 305, 566 and 630 kg.m(-3) and a free air space of 72%, 48% and 42%, respectively. The heaps were turned after 21 days. Total composting time was 142 days. Results. During the experimentation, the temperature remained high and above 55 degrees C for 40 days for the pure manure heap T, for 29 days for heap B1 and for 34 days for heap B2. During composting, heap T lost 69% of its wet mass and 64% of its initial volume, while heap B1 lost 71% and 44% and B2 lost 68% and 49%, respectively. Heap T lost 54% of its organic matter (OM) and 15% of its initial nitrogen (N); the respective levels of loss for B1 were 51% and 42% and for B2 56% and 50%. The heterogeneity of the dry matter (DM) and N content decreased during composting for heaps T and B1, whereas it increased for heap B2. Conclusions. The composts obtained were in accordance with the French standard NFU 44- 051 (T) and the French standard NFU 44- 095 (B1 and B2), except for the DM content criterion for B1 and B2. Relative to bovine manure compost, compost with the addition of sludge (1/3) was found to be enriched (on a fresh weight basis) in N (+ 15%), in P (+ 40%), whereas it was depleted in K (- 20%).

The dairy sludge elimination is still not optimized in Reunion Island as it is currently dumped in landfills. The aim of this study is to investigate the co-composting of dairy sludge with cattle manure. Three heaps were formed using cattle manure mixed with dairy sludge in the following proportions: M - 1 + 0, S1 -2/3 + 1/3 and S2 - 1/2 + 1/2. The heaps were turned after 21 days. Total composting time was 142 days. During the experimentation, temperature remained high and above 55°C during 46 days for the pure manure pile M, 32 days for S1 pile and 36 days for S2 pile. During composting, M has lost 69% of its fresh mass and 64% of its initial volume while 71% and 44% respectively for S1 and 68% and 49%, respectively for S2. Heaps have lost from 44% to 49% of the initial organic matter and the windrows formed with sludge lost more nitrogen than the pure manure one (M - 52%, S1 - 69% and S2 - 66% of its initial nitrogen). (Resume d'auteur)

Ce recueil abondamment illlustre rassemble les itineraires techniques mis au point au cours des dix dernieres annees avec l'aide des agriculteurs de cette partie de l'ile. Le but de ce travail etait la gestion des terres par des pratiques culturales judicieuses vis-a-vis de la fertilite. Les donnees sont presentees en fiches, lesquelles concernent les diverses especes cultivees sur place, associees ou non (alimentaires, fruitieres, fourrageres, a parfum...) et s'adressent aussi bien aux producteurs qu'a leurs partenaires, agents de la formation et du developpement

Contexte. Les crotalaires (Crotalaria spp.) sont des légumineuses (Fabaceae) utilisées comme plantes de service (PdS) pour couvrir le sol et ainsi réduire l’érosion, l’enrichir en azote par fixation symbiotique, et assurer une fonction assainissante vis-à-vis de bioagresseurs telluriques comme certains nématodes (1). A La Réunion, plusieurs espèces de crotalaires sont ainsi évaluées en vue de leur inclusion dans des systèmes de culture (SdC) à base d’ananas et de canne à sucre, dans une démarche de transition agroécologique. Il s’agit principalement de Crotalaria juncea L. et C. spectabilis Roth. Malheureusement, ces espèces subissent depuis peu des attaques de la punaise miride Moissonia importunitas (2)(Figs.1&2) si importantes qu’elles remettent en cause leur culture. Trois leviers techniques potentiels ont été évalués dans un premier temps pour gérer ce ravageur sans recours à des pesticides chimiques, ou à défaut écarter les crotalaires comme PdS dans les SdC réunionnais, à savoir : i) la culture de la crotalaire en association avec d’autres espèces de PdS ; ii) le traitement de la crotalaire avec des produits de protection des plantes (PPP) non chimiques ; iii) le choix de l’espèce de crotalaire.