Effect of planting date on severity of frogeye leaf spot and grain yield of soybeans

The influence of soybean (Glycine max) planting date on seasonal epidemics of frogeye leaf spot caused by Cercospora sojina and on grain yield, was evaluated during the 1991 and 1992 cropping seasons. Two susceptible (Samsoy 1 and TGx 849-313D) and one resistant (TGx 996-26E) soybean cultivars were used in field trials at Zonkwa, in the southern Kaduna state of Nigeria. Four field plantings were made at 14-day intervals from late May to mid0July. For each planting date, half the plots received foliar applications of benomyl at R₁ and R₃ growth stages, and the other half was untreated. Frogeye disease severity ratings were taken for all plots at R₄ to R₅ growth stages, and grain yield for each plot was measured at harvest. There was a significant (p < 0.05) increase in disease severity between the first and third plantings on the two susceptible cultivars in 1991, and on TGx 849-313D only in 1992. Corresponding yield reductions for the two susceptible cultivars averaged 13 and 31% for the treated and untreated plots, respectively, with each 2-week delay beyond the first planting date in 1991, and 5 and 6%, respectively, in 1992. There was no significant difference in disease among all treatments on the resistant cultivar, TGx 996-26E. Under Nigerian conditions, an increase in frogeye leaf spot severity can be expected with delayed planting of soybean after 1 June, and this can result in a corresponding loss of crop yield.     

The impact of the locust control insecticide fipronil on termites and ants in two contrasting habitats in northern Australia

Termites and ants are key ecosystem engineers and nutrient re-cyclers. Extensive spraying of insecticides presents a hazard to these insects. Using a control-treatment paired design comprising 3 replicate pairs of plots per soil type, we quantified the impact of fipronil on termite consumption of cardboard and wood baits, termite repair of deliberately damaged mounds as well as ant community composition and abundance in two different habitats (black vertisol and red kandosol soil) when applied aerially at a dose rate recommended for locust control in Australia. The study was conducted from 2006 to 2008. The diversity of termites and ants was higher and side-effects were more pronounced on kandosol than on vertisol soil. Overall termite consumption of cardboard baits was significantly greater in unsprayed than in sprayed plots while losses were significantly greater in only one (vertisol) or two (kandosol) sprayed plots, respectively, compared to paired unsprayed plots. In the first year, termite consumption of wood baits was generally significantly greater on unsprayed than on sprayed kandosol while only marginally significant on unsprayed vertisol. Again, losses were significantly greater in one (vertisol) and two (kandosol) sprayed plots, respectively, compared to paired unsprayed plots. Overall termite consumption of wood baits was similar among plots in the second year post-spray although consumption remained significantly depressed in one pair of sprayed plots in each habitat. The capacity of the mound-building termite, Drepanotermes rubriceps (Froggatt) unique to kandosol, to repair damaged mounds was significantly reduced by fipronil. Furthermore, colonies of Iridomyrmex greensladei Shattuck, an ant species associated with mounds of D. rubriceps, were not re-located five months post-spray. Ant communities were also adversely affected. On vertisol, species richness and relative abundance were similar among treatments, but significantly fewer species were caught in one individual sprayed plot. In contrast on kandosol, species richness and relative abundance were significantly reduced by fipronil. A drop in species richness was observed in all and a drop in relative abundance in two sprayed plots. On vertisol, abundances of two species were significantly lower in sprayed than in paired unsprayed plots. Likewise on kandosol, abundances of five species were significantly reduced in sprayed plots, and one species was not caught at all. The weight of evidence of our findings indicate that fipronil, even at a low rate, will have substantial adverse impacts on the diversity and activity of termites and ants, especially if applied within one to two years of earlier applications.     

Evaluation of soybean genotypes for field resistance to stink bugs in Nigeria

A number of soybean breeding lines and other genotypes were screened for resistance to stink bugs under field conditions at two locations (Mokwa and Ibadan) in Nigeria using two dates of planting (DOP) and no insecticides for 2 years. Stink bug populations were high during the first year and moderate the second year. Bug damage to pods was scored in the field and seed damage assessed in the laboratory using plant samples obtained from the field. Overall, damage was greater in Mokwa than in Ibadan. Visual damage scores ranged from 4·0 to 9·0 (scale 1–9) during the first DOP in the first year at Mokwa and 2–6 during the second DOP. During the second year, damage scores ranged from an average of 3·8 to 4·9 for both DOPs. Seed damage ranged from an average of 32% to 59%. Visual damage scores were negatively correlated with yield, such that lower yields were obtained where higher scores were given. Our results show that pod and seed damage was often greater in the upper portion of the plant in the varieties tested, thus indicating where the feeding activity of the insects was concentrated. A seed damage ratio (SDR) is computed and used, among other parameters, to select TGx 713-09D, TGx 307-048D, TGx 306-036C and TGx 814-036D as the genotypes manifesting the highest level of field resistance. These results are discussed in relation to the development of soybean varieties resistant to stink bugs.     

Yield,protein, and oil quality of soybean genotypes selected for tofu production

The soyfood industry prefers some soybean [( Glycine max L. (Merr.)] cultivars over others based on chemical constituents, physical traits, and processing quality of the seed. However, soybean cultivars possessing the combination of desirable agronomic traits and biochemical characteristics that enhance the quality of soyfoods have not been identified in the U.S. Thus, this research was conducted with the objective of determining yield, seed protein, and fatty acid composition of soybean genotypes selected for tofu production. Twelve soybean genotypes were planted in plots arranged in a randomized complete block design with four replications at the Agricultural Research Station, Fort Valley State University, Georgia during 1994 and 1995. Seed yield ranged from 1.6 to 3.0 metric tons/ha. The protein content varied between 314.2 and 480.7 g/kg seed. Both BARC-8 and BARC-9 had significantly higher protein content than other genotypes. These two genotypes also showed significant year by genotype interactions for some fatty acids. V71-370 had the highest oleic acid concentration and a high ratio (0.92) of monounsaturated to polyunsaturated fatty acids. The concentration of linoleic and linolenic acids ranged from 406.5 to 531.0 and 37.1 to 63.0 g/kg oil, respectively. Seed yield was correlated with biomass, harvest index, and filled pods per m2. In this study, V71-370 was found to be relatively superior in oil quality with fatty acid composition desirable for human consumption. The significant variation for seed yield and biochemical characteristics observed among the few genotypes examined in this study indicates the potential for breeding high yielding soybean cultivars suitable for soyfoods. Therefore, there is a need for evaluation of soybean germplasm for agronomic traits that contribute to seed yield and biochemical characteristics including fatty acid profiles that enhance soyfood quality before initiating development of suitable cultivars for tofu.     

Clonal performance of perennial Oryza sativa/O. rufipogon selections and their combining ability with O. sativa cultivars for survival, stolon production and yield

In Southeast Asia, upland rice (Oryza sativa) is an annual crop typically grown for subsistence on hilly lands that are at risk for soil erosion. If perennial cultivars of upland rice were developed, they would provide farmers with an inexpensive tool to produce a preferred food while conserving soil. O. rufipogon, the undomesticated progenitor of O. sativa, includes perennial and stoloniferous forms. To evaluate the feasibility of developing perennial cultivars by combining genes of O. sativa and O. rufipogon, four trials were conducted in an upland field at IRRI: O. sativa/O. rufipogon F₁ clone and cutting height trial, F₂ family trial, and two O. sativa/stoloniferous-selection factorial mating design trials. Plants were established at the beginning of the rainy season, then subjected to a 6-month dry season and evaluated for survival after 1 year. Of the 2101 cultivar control plants, only three IR47686-1-4-B individuals survived and none produced stolons. The 18 F₁ clones, which were selected from previous trials with less drought stress, ranged in survival from 4.4 to 91.4%. Cutting height at harvest did not affect survival. Survival among the F₂ families ranged from 9.4 to 31.9%. Segregation for stolon presence did not differ from a 3:1 ratio for five of the six F₂ families, suggesting the effect of a single dominant gene. Average yields per plant for the F₂ families were 1/3 to 1/9 of yields for the cultivars. However, by crossing the F₁s to cultivars, yield potential was almost fully recovered. For the full-sib families of the factorial trials, survival ranged from 0.0 to 48.6%. Azucena and IR47686-1-4-B, both japonica cultivars, exhibited greater general combining ability for survival relative to the six other cultivar parents. Thus, the process of developing perennial cultivars of rice should include screening annual cultivars to identify those with the best combining ability for survival. To develop cultivars of perennial upland rice, drought avoidance and/or tolerance from annual upland cultivars must be combined with the capacity for perennial growth from wild perennial species. The frequency of stolonifereous testcross progeny was lower than expected and was affected by the O. sativa parent. Thus, additional genes likely affected stolon penetrance and expression. Analyses of covariance indicated that stolons improved the likelihood of survival for progenies of the factorial trials but the effect was small (b < 0.1), and that yield (g/plant) had a small negative effect on percent survival (b = −0.13 to −0.32). This study demonstrated that it was possible to introgress genes for perennial growth from wild O. rufipogon accessions into domesticated O. sativa. Additionally, strategies for developing perennial cultivars of upland rice were improved.     

种植抗虫品种和减量使用杀虫剂的白背飞虱可持续治理技术的田间试验

采用田间虫情和天敌数量调查、水稻产量与千粒重测定和水稻生产实际收益比较的方法,在浙江富阳和重庆秀山两地进行了种植抗虫品种和减量使用杀虫剂的白背飞虱可持续治理技术的田间试验.设使用杀虫剂2次和农户管理(使用杀虫剂4～5次)两个处理,无杀虫剂作为对照.试验结果表明,抗虫品种嘉花1号在各种杀虫剂处理中,白背飞虱成、若虫数量最低(0.9～3.3只/株),是感虫品种中香1号无杀虫剂处理的0.12%.无杀虫剂处理的蜘蛛数量分别是农户管理和杀虫剂2次处理的2.8～5.5倍和1.6～4.1倍.在同样的杀虫剂处理条件下,抗虫和耐虫品种的稻谷损失量和损失率较感虫品种明显地低.水稻生产的实际收益比较显示,无杀虫剂处理,种植嘉花1号可以增收1.13%～15.91%.因此,稻农种植抗虫或耐虫品种,减量使用杀虫剂至2次或不使用杀虫剂,充分利用蜘蛛等天敌的控制作用,完全能够有效地抑制白背飞虱种群的发生和发展,获得与常规杀虫剂用量(4～5次)相仿或更高的收益.     

Alternate-row treatment with the repellent methiocarb to protect cherry orchards from birds

An alternate-row treatment of the bird repellent methiocarb (CA chemical name 3, 5-dimethyl-4-(methylthio)phenyl methylcarbamate; Mesurol® was evaluated for protecting entire cherry orchards from damage by European starlings, American robins, house finches, common grackles and other birds. Half of each orchard was randomly selected for treatment with methiocarb (1·7 kg/ha) applied to trees in every other row. The other half of each orchard was used as a control. Estimated loss of cherries to birds at the time of damage assessment was significantly lower in the six partially sprayed blocks (6·5%) than in the six unsprayed, control blocks (8·8%) (P = 0·03). However, the level of bird damage and the magnitude of the reduction were insufficient to provide a favourable benefit:cost ratio: there was a return of only $0·80 in cherries saved for every $1·00 spent on application and chemical costs. The overall lower damage in the partially sprayed blocks appeared to result primarily from reduced feeding by birds in the sprayed trees, which averaged 4·6% loss compared with 8·4% loss for unsprayed trees within the same block (P = 0·22). That this difference was not statistically significant indicates that birds had to sample a substantial number of berries before discriminating between sprayed and unsprayed fruit. It is not clear how birds detected berries sprayed with the repellent. Suggestions for evaluating other partial treatments of bird repellents in cherry orchards are discussed.     

Fungicidal disease suppression and yield losses associated with sunflower rust in Israel

The effects of rust on the yield components and harvested achene yield of a non-oilseed sunflower cultivar were examined in two field trials in Israel. Head area and the number of achenes per head were decreased during severe rust epidemics, but were unaffected by moderate or mild epidemics. Individual achene weight and the frequency of fertile achenes were influenced by the disease, in relation to its intensity. The fungicide tebuconazole, applied at a rate of 0.125 kg a.i. ha⁻¹, arrested rust development for at least 14 days. Highly significant effects were obtained by spraying when anthesis had occurred only in the outer quarter of the inflorescence radius, whereas the effects of spraying when anthesis was completed were negligible. Differences in yield (0.86–1.15 t ha⁻¹) and in net profit (US$696–1153 ha⁻¹) between sprayed and unsprayed plots were significant (p<0.05).     

溴虫腈在菜用大豆上残留动态及安全使用技术

采用气相色谱（GC-ECD）及田间试验方法,研究了溴虫腈在菜用大豆中的残留消解动态和安全使用技术。结果表明,溴虫腈在菜用大豆上的原始残留沉积量因不同施药处理而有所差异。其残留消解动态符合一级动力学关系,相关系数（︱r︱）=0.9438-0.9847（P〈0.01）;早季的消解系数（︱k︱）=0.13555±0.001955,半衰期（T1/2）为5.0-5.2 d,消解99%所需要的时间（T0.99）为33.5-34.5 d;晚季的︱k︱=0.12748±0.00268,T1/2为5.3-5.6 d,T0.99为35.4-36.9 d。按常规施药方法,在菜用大豆上施用溴虫腈（112.50 g·hm^-2）,在施药1次后17 d,早季豆的农药最终残留量为0.448 mg·kg^-1,晚季豆的农药最终残留量为0.519 mg·kg^-1;连续施药2次（间隔7 d）后22 d,早季豆的农药最终残留量为0.459 mg·kg^-1,晚季豆的农药最终残留量为0.536 mg·kg^-1,产品质量安全水平均符合美国规定的最高残留限量标准。     

收获期籽粒田间霉变对大豆产量和品质的影响

为明确收获期籽粒田间霉变对大豆产量和品质的影响,采用人工降雨室内模拟连阴雨天气,对18个大豆材料进行高湿诱导霉变处理,通过籽粒霉变程度分级,比较不同材料间的霉变敏感性差异,同时考察霉变对大豆产量和品质的影响。结果表明,不同大豆材料对籽粒田间霉变的敏感性存在显著差异,黑色和棕色种皮大豆较黄色种皮大豆的霉变抗性更强。霉变使各大豆材料产量显著下降,产量损失在23.14%~96.55%之间,产量损失率与霉变指数呈极显著正相关(P0.01),产量损失率(Y)与霉变指数(X)的回归拟合方程为Y=1.34X+24.51,R=0.98。霉变还影响大豆品质,籽粒蛋白质、脂肪的相对含量随霉变程度的增加先降低后升高,可溶性糖的相对含量随霉变程度的增加而降低,而蛋白质、脂肪和可溶性糖的绝对含量均随霉变程度的增加而降低。此外,霉变使籽粒百粒重降低,并随霉变程度的增加而逐步降低。大豆收获期籽粒田间霉变会对大豆产量和品质产生不利影响,不同抗性的大豆种质资源为抗霉变大豆品种的选育提供了物质基础。     

Yield and economics of traditional and early soybean production system (ESPS) seedings in the midsouthern United States

Drought stress reduces yield of traditional May and June seedlings of soybean in midsouthern USA. Field experiments using Maturity Group (MG) IV and MG V soybean cultivars were conducted at Stoneville, Mississippi (latitude 33°26′ N) for five years to determine effects of earlier-than-normal (April) and normal (May) seeding on net returns from soybean grown with, and without, irrigation. Net returns were calculated as the difference between income and all direct and indirect costs excluding those for land, management, and general farm overhead. In the irrigated environment, average net returns from April seedings of MG IV cultivars were greater than those from May seedings in all years, while average net returns from April seedings of MG V cultivars were greater than those from May seedings in all years except 1997. These greater net returns resulted from larger seed yields, lower estimated costs, higher prices received for harvested seed, or a combination of the three. Average net returns from April seedings ranged from US$ 148 to US$ 617/ha, while average net returns from May seedings ranged from US$ 69 to US$ 567/ha. Use of MG IV vs. MG V cultivars had no consistent effect on net returns from either April or May seedings. In the nonirrigated environment, average net returns from April seedings of all cultivars were greater than those from May seedings in all years. Average annual net returns from cultivars seeded in April ranged from US$ 74 to US$ 374/ha, while average annual net returns from May seedings ranged from US$ −9 to US$ 325/ha. In three of the five years, MG V cultivars sown in April produced more yield and greater net return than did MG IV cultivars, while April-sown MG IV cultivars produced the highest yield and net return in one of the five years in the nonirrigated study. These results indicate that earlier-than-normal (April) seedings of either MG IV or MG V soybean cultivars will result in increased net return vs. that attained from traditional (May or later) seedings in the midsouthern USA. These results also indicate that choosing cultivars within an MG is more critical than choosing between MG IV and V.     

Effects of combined application of potassium phosphite and fungicide on stem and sheath disease control,yield, and quality of rice

Phosphite has been shown to suppress some diseases in different plant species but disease control in rice has not been investigated. In 2012/13 and 2013/14 potassium phosphite was sprayed at 1775 g ha⁻¹ and 3550 g ha⁻¹ in field plots of rice in Uruguay to determine if phosphite alone or in combination with label rates of a mixed strobilurin and triazole fungicide could be used to effectively control stem rot and aggregate sheath spot in irrigated rice. Six treatments consisting of different combinations of potassium phosphite alone or with a fungicide and an unsprayed control were assayed in one application at late-boot to early-heading. Phosphite alone in single and double rate slightly reduced severity and incidence of stem rot and produced a small yield increase over the unsprayed control. Fungicide at a 50% label rate with phosphite reduced stem rot severity and incidence to a similar level as the fungicide alone applied at the label rate. Disease severity was reduced by approximately 25% and incidence by 17–20% when compared with untreated control. Yield increase was 5% for both treatments over the unsprayed control. Fungicide combined with phosphite at single and double rates reduced stem rot severity by 40–45% and incidence by 34–38% when compared with untreated control, with yield increased by 10% over the unsprayed control and 5% over plots treated with a fungicide. These results indicate that a single application of potassium phosphite combined with fungicide can be used efficiently to manage of rice stem diseases.     

Yield and dry matter productivity of Japanese and US soybean cultivars

The difference in yields of cultivars may be causing difference in soybean yield between Japan and the USA. The objective of this study was to identify the effect of the cultivar on dry matter production and to reveal the key factors causing the differences in yield by focusing utilization of solar radiation in recent Japanese and US soybean cultivars. Field experiments were conducted during two seasons in Takatsuki, Japan (34°50′), and in a single season in Fayetteville (36°04′), AR, USA. Five Japanese and 10 US cultivars were observed under near-optimal conditions in order to achieve yields as close to their physiological potential as possible. The seed yield and total aboveground dry matter (TDM) were measured at maturity as long as radiation was intercepted by the canopy. The seed yield ranged from 3.10t ha^?1 to 5.91t ha^?1. Throughout the three environments, the seed yield of US cultivars was significantly higher than that of Japanese cultivars. The seed yield correlated with the TDM rather than the HI with correlation coefficients from .519 to .928 for the TDM vs. .175 to .800 for the HI, for each of the three environments. The higher TDM of US cultivars was caused by a higher radiation use efficiency rather than higher total intercepted radiation throughout the three environments. The seasonal change in the TDM observed in four cultivars indicated that dry matter productivity was different between cultivars, specifically during the seed-filling period.     

Leaf and seed micronutrient accumulation in soybean cultivars in response to integrated organic and chemical fertilizers application

Plant nutrients can be influenced by organic materials of soils. An experiment was conducted to evaluate the effect of organic amendments on elements uptake by soybean cultivars in a silty loam soil in Mazandaran province, Iran. The experiment was carried out in split plot based on randomized complete block design with three replications in 2006. Main plots were included 8 fertilizer treatments consisted of 20 and 40 Mg ha(-1) Municipal Solid Waste Compost (MSW), Vermicompost (VC) and Sewage Sludge (SS) which enriched with 50% chemical fertilizers needed by soil, only chemical fertilizer treatment and control. Sub plots consisted of three genotypes of soybean (032, 033 and JK). Grain yield was determined and soybean leaves and seeds were digested and analyzed for Mn, Cu, Zn and Fe. Results showed that yield and elements content in soybean leaves and seeds (Mn, Cu, Zn and Fe) were influenced by all treatments. The 40 Mg ha(-1) of sewage sludge enriched with chemical fertilizers produced maximum grain yield. Different soybean cultivars had also significant differences in terms of leaf and seed micronutrients accumulation. Maximum grain yield was observed in JK and 033. Mean comparisons showed that interaction effects of fertilizer and cultivar had significant differences on Mn, Cu and Fe content in soybean leaves, so that the maximum Cu content was observed in 032 cultivars with 40 Mg ha(-1) enriched sewage sludge and municipal waste compost. Also the highest amount of Fe was obtained for JK cultivar when the 40 Mg ha(-1) of municipal compost was used. Among different mentioned traits, Fe and Cu content in leaf and seed and Zn content in leaf had a positive and significant correlation with grain yield.     

川东南轻简栽培方式再生稻产量构成特征和经济效益分析

为了探明轻简栽培方式对中稻+再生稻产量构成特征和经济效益的影响,以黄华占和金农丝苗为材料,于2017年在四川泸州进行不同栽培方式(翻耕移栽、翻耕直播、免耕移栽)的大田试验,分析了中稻-再生稻干物质生产特性、产量、产量构成和经济效益.结果表明,不同栽培方式间头季稻产量差异不显著.翻耕直播头季稻产量较翻耕移栽平均增加3.5...     

大豆花叶病毒（SMV）流行的产量损失及其模型预测

网室接种和田间调查测定SMV引致大豆的产量损失证明,SMV侵染大豆植株愈是在生育早期产量损失愈重。盛花期以后发病的植株产量损失显著减小,鼓粒初期的病株几乎无产量损失。SMV不同毒株引致的产量损失显著不同,强毒株的侵染,引致感病品种的产量损失平均超过弱毒株的40％。根据不同初侵染水平的30组SMV流行与产量损失数据,采用逐步回归分析,建立了准确度较高的产量损失预测多点模型和单点模型。根据损失测定,大豆盛花期的SMV病株率低于3％可控制SMV流行所造成的产量损失。     

Coleoptile length variation of near-isogenic Rht lines of modern CIMMYT bread and durum wheats

A set of 10 bread wheat (Triticum aestivum L.) and six durum wheat (T. turgidum L.) genotypes near-isogenic for either the Rht1 or Rht2 dwarfing genes were analyzed for plant height, kernel weight, coleoptile length and grain yield. Coleoptile length was measured at three different temperatures and plant height, kernel weight and grain yield determined in six different environments. Durum wheat, regardless of stature, produced longer coleoptiles than bread wheat at higher temperature. Within the non-Rht isolines, plant height and coleoptile length were independent characters. The tall durum wheats tended to be taller than their bread wheat counterparts, indicating an absence of minor genes for reduced height. However, a number of bread wheat cultivars showed relatively small height increases following removal of the Rht gene and substantially greater increases in coleoptile length. Coleoptile length was more highly correlated (r²=0.53, P<0.01) with seed weight among the non-Rht isolines compared to cultivars containing either Rht1 or Rht2. Grain yield and plant height were positively correlated among the semi-dwarf Rht isolines in 5 of 6 environments. No equivalent relationship existed among the non-Rht materials. Grain yield (standard sowing depth 3 cm) and coleoptile length were generally not significantly correlated within each isogenic grouping.

Plant breeders should be able to select short statured, non-Rht1 or non-Rht2 hexaploid bread wheat with better emergence characteristics. The non-Rht genotypes developed from the bread wheat cultivars Seri 82 and Culiacan 89 were identified as meeting these criteria. Wheats such as these could offer significant advantages to farmers in environments where deep sowing into stored soil moisture is practiced.     

播期对不同类型专用大豆生长特性和产量的影响

用早毛豆、夏大豆、特用豆和芽用豆类计18个大豆品种(系)为材料研究了不同播期对大豆生长和产量的影响.结果表明:播期对早毛豆各品种的全生育期无明显的影响,而其它类大豆品种的全生育期均随播期的延迟而缩短.除早毛豆外,大豆株高、单株分枝数、单株成英数和单株产量多随播期的延迟而降低;百粒重在35g以下的,播期对百粒重的影响不甚明显.     

干旱胁迫对亚有限大豆植株鲜重建成与分配的影响

通过控水盆栽试验,分别在大豆始花期、始粒期和全生育期进行干旱胁迫,分析干旱胁迫对亚有限大豆品种光合产物分配的影响.结果表明:在不同干旱处理下,叶柄鲜重、叶片鲜重、茎秆鲜重、荚皮鲜重、籽粒鲜重、根鲜重、根瘤鲜重和单株根瘤数均随着干旱胁迫强度加大而下降.在全生育期和始花期干旱胁迫下,地上鲜重占总鲜重的比例随干旱程度的增加而...     

Intercropping cassava with soybean cultivars of varying maturities

Our previous work has shown that early-maturing soybean is suitable for intercropping with vassava at a high latitude (27°S) in south-east Queensland, Australia, as it does not effect the tuber yield. The present study examines whether later-maturing cultivars of soybean with higher yield potential might be more productive. Plant arrangement for cassava was the same in sole crop and in intercrop, while two soybean rows in every six rows were replaced by a row of cassava in intercropping.All soybean cultivars dominated intercropped cassava, and their dry-matter growth and seed yield were not affected by competition with cassava. Growth of cassava was, on the other hand, severely restricted by intercropped soybean, particularly by late-maturing types. After removal of early-maturing soybean, cassava recovered quickly to produce high leaf-area and effectively intercepted solar radiation. Consequential high total dry-matter production, combined with high assimilate allocation to tubers, resulted in tuber yield at the final harvest similar to that in sole cassava. After the removal of late-maturing soybean, however, recovery was poor, and with a short growing season remaining, tuber yields were only 50–60% of that of sole cassava.In addition to their adverse effect on cassave growth, late-maturing cultivars were not suitable as an intercrop because of low harvest indices and low light-conversion efficiency (dry matter produced per unit intercepted radiation), although total light interception during the whole growth of cassava/soybean intercrop was similar to that of sole cassava. The low overall light-conversion efficiency in intercropping with late-maturing cultivars was due to very low dry-matter production of soybean during pod-filling when light interception was still high.