Relay Intercropping System Research Articles

Rice (Oryza Sativa) and chickpea (Cicer Aritinum L) relay intercropping systems in an additive series experiment in rain fed lowland ecosystem of fogera vertisols

Study on rice as a main crop-chickpea as a companion crop relay intercropping in an additive series experiment in rain fed lowland ecosystem of Fogera vertisols was conducted for two consecutive years to test the rice-chick pea relay intercropping planting method and to determine the optimum proportion for component crops in rice- chick pea relay intercropping on transplanted rice. The experiment was conducted in randomized block design with three replications. Five seed rates of chick pea relayed intercropped in between rows of transplanted rice and one sole rice were tested i.e. full recommended seed rate of chick pea relay intercropped in between rows of transplanted rice, two-third of the recommended seed rate of chick pea relay intercropped in between rows of transplanted rice, two-third of the recommended seed rate of chick pea relay intercropped in between alternate rows of transplanted rice, half of the recommended seed rate of chick pea relay intercropped in between rows of transplanted rice, half of the recommended seed rate of chick pea relay intercropped in between alternate rows of transplanted rice and the sole transplanted rice used as comparison. Rice yield and yield component data were statistically subjected to analysis of variance using SAS-JMP-5 software. All growth, yield and yield component of rice did not significantly affected by additive relay intercropping and seed proportion in rice-chickpea relay intercropping systems. However, the study conducted for two consecutive years at all test sits confirmed that chick pea after twenty days from the planting time was completely dried and unable to gave seed yield from rice-chickpea relay intercropping experiment. Hence, under current crop management practice of rice at Fogera vertisol areas, relay intercropping of chickpea with rice is not economically important for farmers.

Characteristics of Nitrogen Uptake, Use and Transfer in a Wheat-Maize-Soybean Relay Intercropping System

Intercropping and relay intercropping systems, which significantly improve land use efficiency, are used worldwide to increase crops yield. The wheat-maize-soybean relay intercropping system has been widely employed by famers in Southwestern China for years, but the detailed mechanisms through which the nitrogen fertilizer use efficiency reach the high level in this system remain unclear. In the present study, two separate pot experiments were performed by 15 N isotope dilution (ID) labeling and direct 15N foliar feeding (FF) assays, and a solid barrier was employed to prevent the roots intergrowth and N movement among crops in the first experiment, using no barrier as the control. The results showed that, under the no-barrier condition, the grain yields, 15N uptake and 15N recovery efficiency of wheat and maize were significantly increased, but those measures in soybean were decreased compared to the solid barrier condition. Furthermore, bi-directional N transfer was detected during the co-growing stage of crops, the amount (Ntransfer) and percentage (%NT) of 15N transferred varied significantly with the fertilizer-N rate, and the maximum reached at 150 – 300 kg N ha–1 level. The Ntransfer from maize to wheat was 16.1% – 163.0% higher than that from wheat to maize; the Ntransfer from soybean to maize was 1.7 – 6.0 times higher than those from maize to soybean, while the %NT from soybean to maize were 6.7 – 22.2 times higher than those from maize to soybean. Conclusively, this study revealed that the interaction of the roots among crops significantly increased the uptake efficiency and recovery efficiency, and further, the positive N competition and bi-directional N transfer of each crops were the main contributors to improve the N use efficiency in the wheat-maize-soybean relay intercropping system.

Influence of Seed Treatment with Uniconazole Powder on Soybean Growth, Photosynthesis, Dry Matter Accumulation after Flowering and Yield in Relay Strip Intercropping System

The relay strip intercropping system of wheat-corn-soybean is widely used in southwest China. However, it is hard to produce soybean stably with this system, since the growth of soybean plants is slower under shading by corn at the seedling stage, and it is compensated by accelerated growth after the symbiotic stage. Soybean plants show excessive vegetative growth due to more rain during the flowering stage, which results in fallen petals, fallen pods and lower yield. This study investigated whether seed treatment with uniconazole powder (0, 2, 4 and 8 mg kg–1 seed) suppresses excessive vegetative growth of soybean plants during the flowering stage and delays senescence of photosynthetically active leaves at the pod-setting stage. If such events are correlated with changes in photosynthesis, they may affect dry matter accumulation and seed yield in the relay stripping system. Uniconazole promoted biomass accumulation from 31 (R3) to 61 (R5) days after flowering (DAF) and seed yield. Seed treatment with uniconazole raised the net photosynthetic rate, stomatal conductance, transpiration rate, and total chlorophyll and chlorophyll a contents. In contrast, uniconazole reduced leaf area index (LAI) from 1 DAF (R1) to 46 DAF (R4) with the increase in uniconazole concentration, whereas, uniconazole significantly increased LAI at 61 DAF, and the greatest promotion occurred at 2 mg kg–1 treatment. The study clearly showed that uniconazole effectively suppressed excessive vegetative growth of soybean during flowering stage, delayed senescence of photosynthetically active leaves at pod-setting stage and induced higher yield, which were related to the changes in photosynthetic rate, chlorophyll content, dry matter accumulation and LAI in the relay strip intercropping system.

Yield Response to Different Planting Geometries in Maize–Soybean Relay Strip Intercropping Systems

Planting geometries directly affect crop yields in intercropping systems. Two different field experiments were conducted in 2012–2013 to analyze how different planting geometries in maize (Zea mays L.) and soybean [Glycine max (L.) Merr.] relay strip intercropping systems at 2:2 maize‐to‐soybean affect yields. Maize plants were planted in narrow‐row planting patterns, whereas soybean was planted in wide rows. The effects of bandwidth, row spacing, plant spacing, and the distance between maize and soybean rows on crop yields were studied. Total intercrop yields were higher than those of sole crop maize and soybean, and the land equivalent ratios of the intercropping systems were above 1.3. The yield of the intercropped maize increased with bandwidth reduction at the same plant density, and similar results were found with increased maize narrow‐row spacing at the same bandwidth. Plant spacing had a dominant function when the bandwidth of the intercropped soybean was >200 cm. By contrast, the distance between maize and soybean rows had a dominant function when bandwidth was <200 cm. The optimum bandwidth and maize narrow‐row spacing in maize–soybean relay intercropping systems were 200 and 40 cm, respectively. These results suggest that the appropriate reduction in the spacing of the narrow maize rows and increase in the distance between maize and soybean rows could be used to achieve high yields in maize–soybean intercropping.

Soil chemical property changes in eggplant/garlic relay intercropping systems under continuous cropping.

Soil sickness is a critical problem for eggplant (Solanum melongena L.) under continuous cropping that affects sustainable eggplant production. Relay intercropping is a significant technique on promoting soil quality, improving eco-environment, and raising output. Field experiments were conducted from September 2010 to November 2012 in northwest China to determine the effects of relay intercropping eggplant with garlic (Allium sativum L.) on soil enzyme activities, available nutrient contents, and pH value under a plastic tunnel. Three treatments were in triplicate using randomized block design: eggplant monoculture (CK), eggplant relay intercropping with normal garlic (NG) and eggplant relay intercropping with green garlic (GG). The major results are as follows: (1) the activities of soil invertase, urease, and alkaline phosphatase were generally enhanced in NG and GG treatments; (2) relay intercropping significantly increased the soil available nutrient contents, and they were mostly higher in GG than NG. On April 11, 2011, the eggplant/garlic co-growth stage, the available nitrogen content in GG was 76.30 mg·kg−1, significantly higher than 61.95 mg·kg−1 in NG. For available potassium on April 17, 2012, they were 398.48 and 387.97 mg·kg−1 in NG and GG, both were significantly higher than 314.84 mg·kg−1 in CK; (3) the soil pH showed a significantly higher level in NG treatment, but lower in GG treatment compared with CK. For the last samples in 2012, soil pH in NG and GG were 7.70 and 7.46, the highest and lowest one among them; (4) the alkaline phosphatase activity and pH displayed a similar decreasing trend with continuous cropping. These findings indicate that relay intercropping eggplant with garlic could be an ideal farming system to effectively improve soil nutrient content, increase soil fertility, and alleviate soil sickness to some extent. These findings are important in helping to develop sustainable eggplant production.

Growth and photosynthetic responses of soybean seedlings to maize shading in relay intercropping system in Southwest China

Intercropping, a traditional and worldwide cropping practice, has been considered as a paradigm of sustainable agriculture based on complementary mechanisms among different crop species. Soybean (Glycine max) is widely relay intercropped about 60 days before maize (Zea mays) harvest in Southwest China. However, shade caused by tall maize plants may be a limiting factor for soybean growth at a seedling stage. In field research, we studied the ecophysiological responses of two widely cultivated soybean varieties [Gongqiudou494-1 (GQD) and Gongxuan 1 (GX)] to maize shading in a relay intercropping system (RI) compared with monocropped soybean plants (M). Our results showed that soybean seedlings intercropped with maize exhibited significantly downregulated net photosynthetic rate (P N) (-38.3%), transpiration rate (-42.7%), and stomatal conductance (-55.4%) due to low available light. The insignificant changes in intercellular CO2 concentration and the maximum efficiency of PSII photochemistry suggested that the maize shading-induced depressions in P N were probably caused by the deficiency of energy for carbon assimilation. The significantly increased total chlorophyll (Chl) content (+27.4%) and Chl b content (+52.2%), with lowered Chl a/b ratios (-20.5%) indicated soybean plants adjusted their light-harvesting efficiency under maize shading condition. Biomass and leaf area index (LAI) of seedlings under RI decreased significantly (-78.7 and -71%, respectively) in comparison with M. Correlation analysis indicated the relative reduction in biomass accumulation was caused by the decline in LAI rather than P N, it affected negatively the final yields of soybean (32.8%). Cultivar-specific responses to maize shading were observed in respects of LAI, biomass, and grain yield. It indicated that GX might be a better cultivar for relay intercropping with maize in Southwest China.

Thrips and Cotton Response to Relay Intercropping with Wheat in North Carolina

In North Carolina, double cropping cotton (Gossypium hirsutum L.) and wheat (Triticum aestivum L.) often results in sub-optimal cotton yield and minimal investment return, most often due to lack of sufficient stand as a result of moisture limitations and a short growing season. Relay intercropping of cotton in wheat prior to harvest may be an alternative to traditional double cropping. A relay intercropping system was tested at five locations over three years in North Carolina to determine thrips infestation, cotton yield, and economic return following relay intercropping of cotton and wheat. Relay intercropped wheat yield ranged from 65% to 85% of conventional wheat plantings. Cotton yields were not affected by the presence of relay-intercropped wheat, but plant maturity was delayed in some experiments. Intercropped cotton plants exhibited similar morphology to cotton planted in a traditional strip tillage system with wheat terminated two wks prior to planting with increased nodes above cracked boll, suggesting delayed plant development. In four of five locations, thrips (Thysanoptera: Thripidae) populations were lower in the intercropped cotton, most likely due to interference of the ability of thrips to locate cotton seedlings. Thrips levels when seed was treated with abamectin plus thiamethoxam plus azoxystrobin and an additional in-furrow application of aldicarb or acephate applied to foliage were less than that of seed treated with azoxystrobin alone. Estimated economic return of intercropped cotton and wheat equaled that of conventional cotton planting and exceeded double cropping of wheat followed by soybean [Glycine max (L.) Merr.] most years when cotton, soybean, and wheat prices were set at $1.98 kg-1 lint, $0.44 kg-1, and $0.25 kg-1, respectively.

Rice (Oryza Sativa) and Chickpea (Cicer aritinum L) Relay Intercropping Systems in an Additive Series Experiment in Rain Fed Lowland Ecosystem of Fogera Vertisols

Study on rice as a main crop and chickpea as a companion crop relay intercropping in an additive series experiment in rain fed lowland ecosystem of Fogera vertisols was conducted for two consecutive years to test the rice-chick pea relay intercropping planting method and to determine the optimum proportion for component crops in rice- chick pea relay intercropping on transplanted rice. The experiment was conducted in randomized block design with three replications. Five seed rates of chick pea relayed intercropped in between rows of transplanted rice and one sole rice were tested i.e. full recommended seed rate of chick pea relay intercropped in between rows of transplanted rice, two-third of the recommended seed rate of chick pea relay intercropped in between rows of transplanted rice, two-third of the recommended seed rate of chick pea relay intercropped in between alternate rows of transplanted rice, half of the recommended seed rate of chick pea relay intercropped in between rows of transplanted rice, half of the recommended seed rate of chick pea relay intercropped in between alternate rows of transplanted rice and the sole transplanted rice used as comparison. Rice yield and yield component data were statistically subjected to analysis of variance using SAS-JMP-5 software. All growth, yield and yield component of rice did not significantly affected by additive relay intercropping and seed proportion in rice-chickpea relay intercropping systems. However, the study conducted for two consecutive years at all test sits confirmed that chick pea after twenty to thirty days from the planting time was completely dried and unable to gave seed yield from rice-chickpea relay intercropping experiment. Hence, under current crop management practice of rice at Fogera vertisol areas, chickpea cannot replace the grass pea in rice-grass pea relay intercropping system (farmers practice); and relay intercropping of chickpea with rice is not economically important for farmers to increase the yield potential and land use efficiency. It needs intensive Agronomy research on rice-chickpea intercropping systems and breeding on both component crops.

Differences of Nitrogen Uptake and Utilization and Nitrogen Regulation Effects in Maize between Maize/Soybean and Maize/Sweet Potato Relay Intercropping Systems

研究西南地区玉米主要2种套作模式下氮素吸收利用差异及氮肥调控效应, 为氮素高效利用提供科学依据。在四川2个玉米主产区, 通过连续4年的大田试验, 对比研究了玉/豆和玉/薯模式下玉米氮素吸收利用差异和不同供氮水平对玉米氮素吸收的调控效应。结果表明, 玉/豆模式下玉米收获期植株中的氮素积累2个试验点平均较玉/薯模式增加7.11%, 氮收获指数增加2.00%左右, 氮素吸收效率增加7.83%, 成熟期籽粒中氮素的分配比例增加1.76%, 而叶、茎鞘中氮素的分配比例分别减少5.85%和2.75%。分带轮作后, 由于不同前茬对土壤养分影响不同, 再加上套作优势, 玉/豆模式下玉米在生长前期就表现出明显的优势, 到收获期植株氮素积累2个试验点平均较玉/薯增加11.85%, 氮素吸收效率增加11.84%。在玉米氮素积累关键时期, 玉/豆模式在低氮处理下玉米植株氮素的积累量显著高于玉/薯模式相同施氮处理, 而在高氮处理下2种模式间差异不大或者表现相反, 氮肥偏生产力、氮素农艺效率和氮肥利用率也有相似的结果; 玉/豆模式在180 kg hm-2施氮量下较其他处理显著提高了玉米氮素农学利用率、氮素吸收利用率和籽粒中氮素的分配量, 玉/薯模式下玉米氮素农学利用率和氮肥利用效率, 在180~270 kg hm-2施氮量处理下较高; 花后氮素同化量玉/豆模式显著高于玉/薯; 2种模式均以施纯氮180~270 kg hm-2处理有利于氮素转运和花后氮素同化量积累。

Effects of relay intercropping maize on rhizosphere soil microbial ecological characteristics in capsicum fields

采用常规稀释平板法、氯仿熏蒸法、BIOLOG GN微平板反应系统及种间根系分隔技术, 以线辣椒单作(SC)为试验对照, 研究了间套作处理[玉米/线辣椒套作+根部塑料膜分隔(ICP)、玉米/线辣椒套作+根部尼龙网分隔(ICM)、玉米/线辣椒套作根部无分隔(ICN)]对线辣椒根际土壤微生物生态特征的影响。结果表明: 整个线辣椒生育期内, 各套作处理线辣椒根际土壤微生物总数与细菌总数具有相同的变化趋势, ICN和ICM处理的真菌、细菌、放线菌数量和细菌/真菌(B/F)、放线菌/真菌(A/F)比值均大于ICP与SC处理。盛果期, ICN处理根际土壤微生物量碳和微生物量氮比同处理其他生育期增加14.2%~54.0%和10.6%~54.7%。各处理土壤微生物群落<i>AWCD</i>的变化随培养时间呈现明显的"S"型曲线。间套作玉米显著提高了线辣椒根际土壤微生物群落的Shannon-Wiener指数(<i>P</i><0.05)、Simpson指数、种间相遇几率和McIntosh指数(<i>P</i><0.05), 并改变了土壤微生物对单一碳源的利用能力。线辣椒根际土壤微生物的不同多样性指数分别与其生物学产量之间存在显著或极显著正相关。说明间套作改善了土壤微生态环境。

Relay intercropping of legume cover crops in organic winter wheat: Effects on performance and resource availability

Wheat yields and grain protein content are lower and more variable in organic conditions than in conventional agriculture, mainly due to nitrogen (N) deficiency and weed competition. The undersowing of legume cover crops in growing winter wheat, also known as relay intercropping, is assumed to be a proficient way of enriching the soil-crop system with N and improving weed control. However, competition for resources may impair wheat performance. Relay intercropping in springtime in growing winter wheat is expected to limit competition for resources from the legume. The aim of our study was to analyze wheat performance and resource competition in relay intercropping systems with legume cover crops under various environmental conditions.Eight field experiments were conducted on organic grain-oriented farms located in southeast France. Black medic (Medicago lupulina), alfalfa (Medicago sativa), red clover (Trifolium pratense) and white clover (Trifolium repens), undersown at wheat tillering stage, were compared with a sole crop of winter wheat (Triticum aestivum cv. Lona). The aerial biomass of wheat and legumes and total N content of wheat were determined at both the flowering stage and harvest time of the wheat. The main trophic resources (water, N and light) were monitored at similar stages. Wheat grain yield and grain protein content were also measured. Sites were classified according to wheat sole crop performance at harvest to evaluate the effect of relay intercropping in the various conditions tested.In all but one of the thirty-two treatments, wheat grain yield was not significantly disturbed by relay intercropping whatever the aerial development of legumes. Abundant aerial development of legumes after flowering (>20% of the aerial biomass of wheat at harvest) was associated with a mean significant decrease in wheat grain protein content of 8.5% of the control treatment value, this occurring in one third of the situations. These ratios of aerial biomasses of legumes compared to wheat were also associated with reductions in soil moisture and wheat N uptake. The effect on the availability of trophic resources for wheat may have led to a decrease in grain protein content without having any effect on grain yield. Sites which registered a low performance for wheat sole crops were less negatively impacted by the presence and aerial development of legumes.The performance of the four legume species and the mechanisms of induced disturbance of resource availability are then discussed. Finally, we try to define ranges of legumes’ development and resource availability in which wheat performance was maintained or limited.

Phosphorus Uptake and Utilization of Maize and Inter-species Interactions in Maize/Soybean and Maize/Sweet Potato Relay Intercropping Systems

采用根系分隔盆栽试验和田间小区试验相结合的方法,通过研究玉米/大豆和玉米/甘薯套作模式下不同分隔方式及不同供磷水平,即0、35、70、105、140 kg P2O5hm 2对玉米磷素吸收利用的影响,阐明两种套作模式下种间相互作用及玉米磷素吸收特性。结果表明,2种套作体系中无论施磷与否,玉米均表现出套作优势（Acs〉0,NCRcs〉1）,且玉米在玉米/大豆套作模式中的竞争能力强于玉米/甘薯模式,大豆和甘薯处于套作劣势,两种模式均促进了玉米磷素积累和产量的提高,施磷70 kg hm 2时,与根系分隔相比,不分隔时玉米磷素积累和产量在玉米/大豆、玉米/甘薯中分别提高了17.05%、5.62%和16.84%、7.17%,磷素当季利用率平均提高了7.81%。种植模式和施磷水平互作效应显著,两种模式均以105 kg hm 2处理玉米茎、叶和穗磷素积累和产量较高,且玉米/大豆套作大于玉米/甘薯套作,说明玉米/大豆模式更有利于玉米磷素的积累及产量的提高。

Agronomic and Economic Comparisons of Double-Crop and Relay-Intercropping Systems of Peanut with Wheat

The climatic conditions of the southeastern US may allow multiple cropping systems of peanut (Arachis hypogaea L.) with wheat (Triticum aestivum L.) to be a sustainable approach toward crop production. The objectives of this project were to determine the agronomic, economic, and weed control viability of double-crop (DC) and relay-intercropping (RI) systems of peanut with wheat. Eight cropping systems including variations of DC, RI, and monocrop (MC) management as main-plots and a sub-plot effect of three peanut cultivars were assessed. Studies were conducted in Tifton, GA, in 2009 and 2011 and Plains, GA, in 2010 and 2011. Differences among yield, grade and Tomato spotted wilt virus (Tospovirus) (TSWV) incidence were significant among cropping systems and genotypes. Double-crop peanut with wheat yielded greater than the RI systems. Georgia-06G and Tifguard had improved results over Georgia Green. Sufficient weed control was attained across all treatments in 2010 and 2011 but not in the RI plots in 2009. Income above variable cost (IAVC) for the DC ($938 to $1875/ha) systems exceeded the potential of RI ($408 to $1210/ha) and most MC ($36 to $1671/ha) treatments. Growers interested in producing peanuts and wheat in the same year would be at an advantage to use a DC system.

Integrating a simple shading algorithm into CERES-wheat and CERES-maize with particular regard to a changing microclimate within a relay-intercropping system

Wheat/maize related multi-cropping systems are the dominant cropping systems in North China. To improve and adjust those systems, and to study competition effects within intercropping, extended field experiments are necessary. As field experiments are time consuming, laborious and expensive, a viable alternative is the use of crop growth models that can quantify the effects of management practices on crop growth and productivity. Field experiments showed that intercropped maize yielded as high as monocropped maize, and grain yield of intercropped wheat increased by up to 32%. Based on a process-oriented modeling approach, this study focuses on analyzing and modeling competitive relationships in a wheat/maize relay intercropping system with regard to yield, solar radiation and microclimate effects. A simple shading algorithm was applied and integrated into the CERES models, which are part of the DSSAT software shell vs. 4.5. The algorithm developed estimates the proportion of shading as affected by neighbouring plant height. The model was tested to investigate the applicability of this shading algorithm within the CERES models in the simulation of grain yield and dry matter yield of wheat and maize. Model error of grain and dry matter yield for both species was below 10%. There was a tendency for grain yield to be simulated adequately but for dry matter yield to be slightly underestimated. Increased top soil temperature in intercropped wheat increased the mineralization of nitrogen and improved N supply. The wheat/maize system was N efficient. Thus, N dynamics were taken into account for simulation as well as CO 2 dynamics based upon modified wind speed. Wheat border rows were exposed to a higher wind speed until mid-June and to reduced wind speed thereafter. As a result, solar radiation, soil temperature and wind speed differed between monocropping and intercropping and could provide a starting point for simulating intercropping. Microclimate effects are often small, subtle or non-existent, while spatial and climate variability and the heterogeneity of plant populations can be considerable. Quantifying microclimatic effects may prove difficult but should not be neglected when simulating intercropping systems.

INTRODUCING AUTUMN SUGARCANE AS A RELAY INTERCROP IN SKIPPED ROW PLANTED RICE–POTATO CROPPING SYSTEM FOR ENHANCED PRODUCTIVITY AND PROFITABILITY IN THE INDIAN SUB-TROPICS

SUMMARYField experiments were conducted for the three consecutive cropping seasons of 2003–05, 2004–06 and 2005–07 at the Indian Institute of Sugarcane Research, Lucknow, India, to explore the feasibility of planting sugarcane in autumn as a relay intercrop in standing rice. The cropping systems evaluated were: i) rice-potato-spring sugarcane; ii) rice + autumn sugarcane (planted as a relay intercrop in every sixth row devoid (skipped) of transplanted rice + potato after rice; iii) rice-autumn sugarcane (planted without preparatory tillage) + potato; and iv) rice-autumn sugarcane (planted with preparatory tillage) + potato. In each case, sugarcane was planted in rows 90 cm apart. Rice was transplanted in rows at 20-cm row spacing when followed by potato or sugarcane, but at 18-cm row spacing when intended for sugarcane planting as a relay intercrop in late September. The germination (60.4%) of cane buds, tillers (323 000 ha−1) and number (149 000 ha−1), length (225 cm), girth (2.44 cm) and weight (747 g) of millable canes were markedly better when autumn sugarcane was planted with rice as a relay intercrop in comparison to other cropping systems. Similarly, this cropping system produced the maximum cane (111.4 t ha−1) and sugar (13.2 t ha−1) along with sugarcane equivalent yield (216.4 t ha−1). In turn, relay intercropping system with maximum cane production efficiency of 420 kg ha−1day−1 fetched the highest economic returns (Rs. 258 ha−1day−1) and benefit:cost ratio (1.5). Compared with the rice-potato-spring sugarcane cropping system, the relay intercrop of autumn sugarcane in standing rice produced 35.4% more cane and 38.3% more sugar with 24.1% higher returns besides 79.1% energy saving. This practice will not only benefit cane growers and sugar mill owners in tropical and sub-tropical India, but also in other parts of the world where rice and sugarcane are extensively cultivated.

Effects of Relay-Intercropping Sorghum With Winter Wheat, Alfalfa, and Cotton on Lady Beetle (Coleoptera: Coccinellidae) Abundance and Species Composition

Creating conditions that enhance the abundance of resident populations of natural enemies in agroecosystems is considered critical to the efficiency of biological control of insect pests. We conducted a study to determine the potential of relay-intercropping for enhancing the abundance of aphidophagous lady beetles in sorghum. A relay-intercropping system consisting of alfalfa, winter wheat, and cotton as intercrops and sorghum as a main crop was compared with sorghum monoculture plots at two study sites in OK from 2003 to 2006. Lady beetles and aphids were sampled throughout the season using sticky traps and field counts on individual sorghum plants. Results from sticky traps and field counts show that differences in abundance and species composition of lady beetles between intercropped and monoculture sorghum were not statistically different during each year of study. Also, the lady beetle-greenbug ratios in relay-intercropped and monoculture plots were not significantly different. Lack of significant effects of relay-intercropping in our study may have been attributable to the confounding effects of spatial and temporal scale and the low number of aphids and other alternative prey in the intercrops compared with high incidence of corn leaf aphids in sorghum early in the season.

Analysis of the productivity of upland rice and cover crops in relay intercropping systems using a mechanistic competition model

Relay intercropping systems with rice cultivars (WAB450-24-3-2-P18-HB (V4) and WAB56-50), the competitive Cajanus cajan and the weakly competitive Stylosanthes hamata were evaluated in the tropical savanna zone in Cote d\'Ivoire. The INTERCOM model for competition served for data analysis and understanding of the system based on phenological, physiological and morphological characteristics of the species. Relationships between accumulated legume biomass and yield loss (YL) in rice showed that rice yield was reduced up to 63 % and 100 % by S. hamata and C. cajan respectively, depending on the introduction time. At low levels of YL both legumes performed similarly. At higher levels of rice YL, C. cajan performed better as it produced higher amounts of biomass. Differences in legume biomass at a specified level of rice YL were mainly created in the growth period following rice maturity, which is restricted by water availability. The lesser performance of S. hamata in that period was attributed to the difference in phenology, combined with the short-duration character of the species. The combination of early introduction and short growth duration of this species prevented a rapid leaf canopy development after rice harvest, resulting in the relatively poor biomass production. Options to improve legume biomass production in relay systems should focus on the period following rice maturity. Les systemes de culture relais avec les varietes de riz (WAB450-24-3-2-P18-HB (V4) et WAB56-50), les especes competitives Cajanus cajan et faiblement competitive Stylosanthes hamata, ont ete evalues en zone savane tropicale de Cote d\'Ivoire. Le modele de competition INTERCOM a servi a l\'analyse et a la comprehension du systeme sur la base des caracteres phenologiques, physiologiques et morphologiques des especes. La relation entre la production en biomasse des legumineuses et les pertes en rendement (PR) du riz ont montre que les rendements en riz ont ete reduits de 63 % et 100 % par S. hamata et C. cajan, respectivement, en fonction de la date de semis. A de faibles niveaux de PR en riz, les deux especes de legumineuses se comportent de facon similaire. A des niveaux eleves de PR, C. cajan est plus performant en produisant des quantites de biomasse plus importantes. Les differences de production en biomasse a un niveau specifie de perte de rendement en riz apparaissent principalement pendant la periode suivant la maturite du riz et qui est restreint par la disponibilite en eau. La faible performance de S. hamata pendant cette periode est attribuee a la difference de phenologie, associee au caractere cycle court de cette espece. La combinaison entre le semis precoce et le temps de croissance reduit n\'a pas permis un developpement rapide de la canopee apres la recolte du riz, entrainant une production relativement mauvaise de la biomasse. Des options pour ameliorer la production de biomasse des legumineuses dans les systemes de culture relais doivent se focaliser sur la periode suivant la maturite du riz Keywords : Legumes, cropping systems, yield loss, Cote d\'Ivoire. Agronomie Africaine Vol. 18 (3)006: pp. 285-298

Nutrient Deficiency in the Rice-Stylo (Stylosanthes guianensis) Relay-Intercropping System in Rainfed Lowland Rice Ecosystem in Northeast Thailand

The rice-stylo (Stylosanthes guianensis) relay-intercropping system in paddy fields has previously been shown to increase agricultural productivity in Northeast Thailand, but successive relay-intercropping conducted without irrigation and fertilization during the stylo cropping has resulted in reduced production of stylo. The aim of this study was to determine the effect of nutrient deficiency on the stylo production. The experiment was conducted using pots to control fertilization accurately. The results showed that, after three successive relay-intercroppings, the soil was severely deficient in sulfur, phosphorus, and molybdenum. Sulfate application to the soil after the successive relay-intercroppings was suggested to improve stylo production. We recommend the use of a rain-fed shallow, favorable subecosystem as a field for stylo production in relay-intercropping and the stylo production with a cycle of several years.

Development and validation of SUCROS-Cotton: a potential crop growth simulation model for cotton

A model for the development, growth and potential production of cotton (SUCROS-Cotton) was developed. Particular attention was given to the phenological development of the plant and the plasticity of fruit growth in response to temperature, radiation, daylength, variety traits, and management. The model is characterized by a comparatively simple code and transparent algorithms. The model was parameterized for Chinese cotton varieties and validated with extensive independent datasets on cotton growth and production from the Yellow River region and Xinjiang Province. The model validation showed that the phenology, growth and yield were simulated satisfactorily. The root mean square error (RMSE) for date of emergence, date of flowering, date of open boll stage and duration from sowing to boll opening was less than four calendar days, both for cotton grown in monoculture and cotton grown in a relay intercropping system with wheat. The RMSE of predicted total dry matter compared with observations was at most 6.6%, of lint yield 6.6%, and for number of harvestable bolls 10.0%. SUCROS-Cotton provides a tool to (1) assess production opportunities of cotton in various ecological zones in response to temperature, incoming radiation and management, (2) identify optimal cotton ideotypes for different agro-ecological conditions and for guiding breeding efforts, and (3) explore resource-use-efficient cropping systems, including intercropping options, and crop management practices such as plastic film mulching and sowing date.

Morpho – physiological characteristics of Cover crops for analysis of upland rice production in relay intercropping systems

To assess the suitability of Leguminous species in rice intercropping systems, physiological and morphological characteristics of Crotalaria juncea, Cajanus cajan, Mucuna pruriens var. cochinchinensis, Calopogonium mucunoides, Aeschynomene histrix and Stylosanthes hamata were determined in monoculture. C. cajan and S. hamata were selected and intercropped with two upland rice cultivars (WAB56-50, WAB450-24-3-2-P18-HB syn. V4) with different competitive ability, at sowing dates ranging from 0 to 84 days after rice sowing (DARS). In monoculture, C. juncea and C. cajan produced nearly 9 ton dry matter ha-1, whereas the other species produced below half this amount. Total N in leaf materials varied between 25 kg and 70 kg ha-1. Based on relative growth rate of the leaves, the height increase rate and total biomass, C. juncea, C. cajan and M. pruriens were identified as potentially most competitive. In intercropping system, a logistic function was adequate to describe rice grain yield, final rice biomass and legume biomass at one week after rice harvest as a function of legume sowing dates. Differences in rice grain yield were significant (P