High productivity of wheat intercropped with maize is associated with plant architectural responses

Mixed cultivation of crops often results in increased production per unit land area, but the underlying mechanisms are poorly understood. Plants in intercrops grow differently from plants in single crops; however, no study has shown the association between plant plastic responses and the yield advantage. Here, we assessed the productivity of wheat–maize intercropping as compared to sole wheat and sole maize, and the associated differences in wheat shoot and leaf traits. In two field experiments, intercrop wheat and maize were both grown in alternating strips consisting of six rows of wheat and two rows of maize. The traits of wheat plants in border rows of the strips were compared to the traits of plants in the inner rows as well as those in sole wheat. Leaf development, chlorophyll concentration and azimuth, as well as the final leaf and ear sizes, tiller dynamics of wheat and yield components of both crops were determined. The relative densities of wheat and maize in the intercrop were 0.33 and 0.67, respectively, but the corresponding relative yields compared to the respective monocultures were 0.46 for wheat and 0.77 for maize. Compared to wheat plants in the inner rows of the intercrop strips as well as in the monoculture, border‐row wheat plants in the intercrop strips had (a) more tillers owing to increased tiller production and survival, and thus more ears, (b) larger top leaves on the main stem and tillers, (c) higher chlorophyll concentration in leaves, (d) greater number of kernels per ear and (e) smaller thousand‐grain weight. Grain yield per metre row length of border‐row wheat was 141% higher than the sole wheat, and was 176% higher than the inner‐row wheat. The results demonstrate the importance of plasticity in architectural traits for yield advantage in multispecies cropping systems.     

黄土塬区玉米大豆不同间作方式对产量和经济收益的影响及其机制

利用不同玉米品种(郑单958和豫玉22)和大豆品种(中黄24和中黄13)在单作和两种(2∶2和2∶4)间作方式下,研究品种、间作方式对间作系统产量和经济效益的影响,探讨其潜在的作用过程和机制,以期为旱区农业高产高效服务。实验结果表明:(1)两种间作方式的土地当量比(LER),相对拥挤系数(K)都高于单作,表明玉米、大豆在两种间作方式下较单作具有显著的间作优势,玉米间作相比单作增产显著。K、实际产量损失(AYL)、侵占力(A)和竞争比率(CR)的变化规律均表明在间作栽培条件下,玉米相对于大豆为竞争优势物种;郑单958相对于豫玉22,中黄24相对于中黄13均占有一定竞争优势。郑单958与中黄24以2∶4比例间作的间作优势(IA)及货币优势指数(MAI)值最高。(2)相比单作,间作种植模式下玉米的水分利用效率明显增加,而且玉米∶大豆以2∶4间作的水分利用效率显著高于2∶2。郑单958与中黄24在2∶4间作方式下的产量和经济效益都最高,适合在当地应用和推广。     

Intercropping enhances soil carbon and nitrogen

Intercropping, the simultaneous cultivation of multiple crop species in a single field, increases aboveground productivity due to species complementarity. We hypothesized that intercrops may have greater belowground productivity than sole crops, and sequester more soil carbon over time due to greater input of root litter. Here, we demonstrate a divergence in soil organic carbon (C) and nitrogen (N) content over 7 years in a field experiment that compared rotational strip intercrop systems and ordinary crop rotations. Soil organic C content in the top 20 cm was 4% ± 1% greater in intercrops than in sole crops, indicating a difference in C sequestration rate between intercrop and sole crop systems of 184 ± 86 kg C ha^?1 yr^?1. Soil organic N content in the top 20 cm was 11% ± 1% greater in intercrops than in sole crops, indicating a difference in N sequestration rate between intercrop and sole crop systems of 45 ± 10 kg N ha^?1 yr^?1. Total root biomass in intercrops was on average 23% greater than the average root biomass in sole crops, providing a possible mechanism for the observed divergence in soil C sequestration between sole crop and intercrop systems. A lowering of the soil δ¹⁵N signature suggested that increased biological N fixation and/or reduced gaseous N losses contributed to the increases in soil N in intercrop rotations with faba bean. Increases in soil N in wheat/maize intercrop pointed to contributions from a broader suite of mechanisms for N retention, e.g., complementary N uptake strategies of the intercropped plant species. Our results indicate that soil C sequestration potential of strip intercropping is similar in magnitude to that of currently recommended management practises to conserve organic matter in soil. Intercropping can contribute to multiple agroecosystem services by increased yield, better soil quality and soil C sequestration.     

Incidence and severity of foliar diseases of sesame (Sesamum indicum L.) intercropped with maize (Zea mays L.)

This study evaluates the effects of different row arrangements on incidence and severity of Cercospora leaf spot (CLS) and Alternaria leaf blight (ALB) diseases and seed health of sesame intercropped with maize. Row arrangements were: sesame intercropped with maize in alternate pair of rows (2:2), two rows of sesame intercropped with one row of maize (2:1), sesame intercropped with maize in single alternate rows (1:1) with sole sesame as control. Intercropping maize with sesame reduced the incidence and severity of diseases. Sesame intercropped with maize in a (1:1) ration recorded a significantly lower number of infected leaves by CLS and ALB incidence than other row arrangements. ALB lesion number was between 17 and 20 in the (1:1) arrangement relative to 65–104 and 28–43 in the sole crop and other row arrangements, respectively. ALB lesion size was also reduced in the (1:1) than other row arrangements. Fungal infection of harvested sesame seeds was significantly reduced in the intercrop relative to the sole crop. CLS incidence was significant and negatively correlated with seed weight while defoliation was significant and positively correlated with ALB or CLS incidence. Rainfall was significant and positively correlated with CLS or ALB incidence while intercropping induced microclimatic effects that influenced disease incidence. Grain yield, weight of 1000-seed, number of capsules/plant and weight of seed/plant were significantly higher in the (1:1) row arrangement than the sole crop or other row arrangements. The study demonstrates that intercropping sesame with maize in a single alternate row (1:1) arrangement can be used to reduce foliar diseases of sesame.     

Crop nitrogen use and soil mineral nitrogen accumulation under different crop combinations and patterns of strip intercropping in northwest China

Increasing crop nitrogen use efficiency while also simultaneously decreasing nitrogen accumulation in the soil would be key steps in controlling nitrogen pollution from agricultural systems. Long-term field experiments were started in 2003 to study the effects of intercropping on crop N use and soil mineral N accumulation in wheat (Triticum aestivum L. cv 2014)/maize (Zea mays L. cv Shendan16), wheat/faba bean (Vicia faba L. cv Lincan No. 5) and maize/faba bean intercropping and monocropping systems. Monocropping was compared with two types of strip intercropping: continuous intercropping (two crops intercropped continuously on the same strips of land every year) and rotational intercropping (two crops grown adjacently and rotated to the other crop??s strip every year). Maize/faba bean intercropping had greater crop N uptake than did wheat/faba bean or wheat/maize. Wheat/maize accumulated more mineral N in the top 140 cm of the soil profile during the co-growth stage from maize emergence to maturity of wheat or faba bean. Continuously intercropped maize substantially decreased soil mineral N accumulation under wheat and faba bean rows (60?C100 cm soil depth) at maize harvest. Soil mineral N accumulation under wheat rows increased with rotational intercropping with faba bean. Rotational intercropping may potentially alleviate the adverse effects of wheat on N use by other crops and increase the nitrogen harvest index of wheat, maize and faba bean. Intercropping using species with different maturity dates may be more effective in increasing crop N use efficiency and decreasing soil mineral N accumulation.     

Influence of spatial arrangement in maize-soybean intercropping on root growth and water use efficiency

Background and aims

The relationship between transpiration and root distribution under different spatial arrangements of intercropping is poorly understood. The effects of three spatial arrangements in the maize (Zea mays L.) - soybean (Glycine max L.) intercropping on root distribution, transpiration, water use efficiency (WUE) and grain yield were examined.

Methods

Two-year field experiments were conducted using three spatial arrangements of 2 rows maize × 4 rows soybean (M2S4), 2 rows maize × 2 rows soybean (M2S2) and 4 rows maize × 2 rows soybean (M4S2), with their respective sole crops (monocrop) for comparison.

Results

The grain yield of maize in intercrops was higher than its monocrop and that of soybean in intercrops was lower than its monocrop. Except for M2S2 in 2014, there were yield advantages in intercropping due to improvement in the land use efficiency. Transpiration in maize was higher than in soybean regardless of the spatial arrangements. Transpiration of both maize and soybean was influenced by the spatial arrangements of the intercropping with M4S2 or M2S4 tending to have higher daily transpiration than monocrops and other spatial arrangements. Intercropping enhanced root length density (RLD) in both maize and soybean compared to the corresponding monocrop. RLD was higher and land equivalent ratio (LER) was lower under M2S2 than under other spatial arrangements of intercropping, WUE was higher in M4S2 than in other spatial arrangements.

Conclusions

Intercropping was more efficient in using the environmental resources than monocropping. The M4S2 spatial arrangement in the maize-soybean intercropping could be selected because of its sustainability and greater land and water use efficiency.

     

Optimum leaf excision increases the biomass accumulation and seed yield of maize plants under different planting patterns

Without developing new agronomic practices, present rates of improvement in seed yields of cereal crops globally are insufficient to fulfil the estimated increasing food demand for 2050 and beyond. Intercropping is one of the agricultural practices that can lead to greater crop yields. However, there exists leaf redundancy for maize in intercropping systems, and the top canopy leaves shade more competent leaves at middle strata of maize plants. Therefore, this work aimed to elucidate the effect of leaf excision treatments in maize to understand the optimum leaf area of maize plants under a maize–soybean relay‐intercropping system (MS_R) and a sole cropping system (SM). The effects of four‐leaf excision treatments (T₁, 0; T₂, 2; T₃, 4; T₄, 6 leaves excised from the top of maize plants until 7 days after silking) on light interception, leaf area index (LAI), photosynthetic characteristics, total biomass accumulation at blistering stage (BS), dough stage (DS) and physiological maturity (PM), and seed yield of maize were investigated through field experiments for 2 years under MS_R and SM. Results showed that, under MS_R and SM, as compared to control (T₁), optimum excision of leaves (T₂) from the top of maize plants significantly improved the light interception (by 25, 18 and 16% at BS, DS and PM, respectively) to lower strata leaves and accelerated the biomass partitioning to maize seeds (by 13 and 12% at DS and PM, respectively). Importantly, plants under T₂ exhibited higher green leaf area than control, that is, excision the top two leaves led to an increase in LAI at PM by 10%, suggesting that leaf senescence under T₂ was delayed which enhanced the photosynthetic rate at PM by 7% in 2017 and 6% in 2018. Relative to T₁, maize under T₂ produced 19 and 13% higher maize yield under MS_R and SM, respectively, and relay‐cropped maize had 90% of SM seed yield. These results suggest that by manipulating the canopy structure of maize plants we can enhance the biomass accumulation and seed yield of maize crops under MS_R and SM.     

Row Ratios of Intercropping Maize and Soybean Can Affect Agronomic Efficiency of the System and Subsequent Wheat

Intercropping is regarded as an important agricultural practice to improve crop production and environmental quality in the regions with intensive agricultural production, e.g., northern China. To optimize agronomic advantage of maize (Zea mays L.) and soybean (Glycine max L.) intercropping system compared to monoculture of maize, two sequential experiments were conducted. Experiment 1 was to screening the optimal cropping system in summer that had the highest yields and economic benefits, and Experiment 2 was to identify the optimum row ratio of the intercrops selected from Experiment 1. Results of Experiment 1 showed that maize intercropping with soybean (maize || soybean) was the optimal cropping system in summer. Compared to conventional monoculture of maize, maize || soybean had significant advantage in yield, economy, land utilization ratio and reducing soil nitrate nitrogen (N) accumulation, as well as better residual effect on the subsequent wheat (Triticum aestivum L.) crop. Experiment 2 showed that intercropping systems reduced use of N fertilizer per unit land area and increased relative biomass of intercropped maize, due to promoted photosynthetic efficiency of border rows and N utilization during symbiotic period. Intercropping advantage began to emerge at tasseling stage after N topdressing for maize. Among all treatments with different row ratios, alternating four maize rows with six soybean rows (4M:6S) had the largest land equivalent ratio (1.30), total N accumulation in crops (258 kg ha^-1), and economic benefit (3,408 USD ha^-1). Compared to maize monoculture, 4M:6S had significantly lower nitrate-N accumulation in soil both after harvest of maize and after harvest of the subsequent wheat, but it did not decrease yield of wheat. The most important advantage of 4M:6S was to increase biomass of intercropped maize and soybean, which further led to the increase of total N accumulation by crops as well as economic benefit. In conclusion, alternating four maize rows with six soybean rows was the optimum row ratio in maize || soybean system, though this needs to be further confirmed by pluri-annual trials.     

Cotton–cowpea intercropping and its N2 fixation capacity improves yield of a subsequent maize crop under Zimbabwean rain-fed conditions

Intercropping cotton (Gossypium hirsutum L.) and cowpea (Vigna unguiculata (L.) Walp) is one of the ways to improve food security and soil fertility whilst generating cash income of the rural poor. A study was carried out to find out the effect of cotton–cowpea intercropping on cowpea N₂-fixation capacity, nitrogen balance and yield of a subsequent maize crop. Results showed that cowpea suppressed cotton yields but the reduction in yield was compensated for by cowpea grain yield. Cowpea grain yield was significantly different across treatments and the yields were as follows: sole cowpea (1.6 Mg ha⁻¹), 1:1 intercrop (1.1 Mg ha⁻¹), and 2:1 intercrop (0.7 Mg ha⁻¹). Cotton lint yield was also significantly different across treatments and was sole cotton (2.5 Mg ha⁻¹), 1:1 intercrop (0.9 Mg ha⁻¹) and 2:1 intercrop (1.5 Mg ha⁻¹). Intercropping cotton and cowpea increased the productivity with land equivalence ratios (LER) of 1.4 and 1.3 for 1:1 and 2:1 intercrop treatments, respectively. There was an increase in percentage of N fixation (%Ndfa) by cowpea in intercrops as compared to sole crops though the absolute amount fixed (Ndfa) was lower due to reduced plant population. Sole cowpea had %Ndfa of 73%, 1:1 intercrop had 85% and 2:1 intercrop had 77% while Ndfa was 138 kg ha⁻¹ for sole cowpea, 128 kg ha⁻¹ for 1:1 intercrop and 68 kg ha⁻¹ for 2:1 intercrop and these were significantly different. Sole cowpea and the intercrops all showed positive N balances of 92 kg ha⁻¹ for sole cowpea and 1:1 intercrop, and 48 kg ha⁻¹ for 2:1 intercrop. Cowpea fixed N transferred to the companion cotton crop was very low with 1:1 intercrop recording 3.5 kg N ha⁻¹ and 2:1 intercrop recording 0.5 kg N ha⁻¹. Crop residues from intercrops and sole cowpea increased maize yields more than residues from sole cotton. Maize grain yield was, after sole cotton (1.4 Mg ha⁻¹), sole cowpea (4.6 Mg ha⁻¹), 1:1 intercrops (4.4 Mg ha⁻¹) and 2:1 intercrops (3.9 Mg ha⁻¹) and these were significantly different from each other. The LER, crop yields, %N fixation and, N balance and residual fertility showed that cotton–cowpea intercropping could be a potentially productive system that can easily fit into the current smallholder farming systems under rain-fed conditions. The fertilizer equivalency values show that substantial benefits do accrue and effort should be directed at maximizing the dry matter yield of the legume in the intercrop system while maintaining or improving the economic yield of the companion cash crop.     

Plant-Plant-Microbe Mechanisms Involved in Soil-Borne Disease Suppression on a Maize and Pepper Intercropping System

Background

Intercropping systems could increase crop diversity and avoid vulnerability to biotic stresses. Most studies have shown that intercropping can provide relief to crops against wind-dispersed pathogens. However, there was limited data on how the practice of intercropping help crops against soil-borne Phytophthora disease.

Principal Findings

Compared to pepper monoculture, a large scale intercropping study of maize grown between pepper rows reduced disease levels of the soil-borne pepper Phytophthora blight. These reduced disease levels of Phytophthora in the intercropping system were correlated with the ability of maize plants to form a “root wall” that restricted the movement of Phytophthora capsici across rows. Experimentally, it was found that maize roots attracted the zoospores of P. capsici and then inhibited their growth. When maize plants were grown in close proximity to each other, the roots produced and secreted larger quantities of 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3(4H)-one (DIMBOA) and 6-methoxy-2-benzoxazolinone (MBOA). Furthermore, MBOA, benzothiazole (BZO), and 2-(methylthio)-benzothiazole (MBZO) were identified in root exudates of maize and showed antimicrobial activity against P. capsici.

Conclusions

Maize could form a “root wall” to restrict the spread of P. capsici across rows in maize and pepper intercropping systems. Antimicrobe compounds secreted by maize root were one of the factors that resulted in the inhibition of P. capsici. These results provide new insights into plant-plant-microbe mechanisms involved in intercropping systems.     

应用热平衡法测定玉米/大豆间作群体内作物的蒸腾量

通过田间试验采用基于热平衡法的茎流计测定玉米/大豆条带间作群体内作物的蒸腾规律.结果表明：间作群体内,玉米和大豆植株的茎流速率在晴天呈单峰曲线,在阴天则呈多峰曲线.植株的茎流受多个环境因子的影响,其中太阳辐射是影响植株茎流最主要的气象因子.玉米和大豆的单株日茎流量与多个气象因子间存在较好的相关关系,达到极显著水平.茎流观测期内（2008年6月1-30日）,间作群体内玉米植株的日均蒸腾量（1.44 mm·d^-1）为大豆（0.79 mm·d^-1）的1.8倍,玉米和大豆植株的蒸腾量分别占间作群体总蒸腾量的64%和36%.考虑到作物的茎直径和叶面积的空间变异,安装一定数量的茎流探头对于准确测定植株茎流是十分必要的.     

Cropping system influences Tomato spotted wilt virus disease development,thrips population and yield of tomato (Lycopersicon esculentum)

Yield of tomato is limited by many diseases including Tomato spotted wilt virus disease. This study was conducted in the field at Kenya Agriculture Research Institute Njoro, Kenya, in 2004 and 2006 to determine the effect of intercropping on disease development, thrips population and yield of tomato variety Cal J grown under four intercrop systems involving kale, onion, maize and sole tomato. The experimental design was a Randomised Complete Block Design (RCBD) replicated three times. Disease scores on tomato–maize differed significantly from tomato–kale and tomato–onion in both years of the study. Maize cropping system had a low significant thrips population from the other cropping systems. Tomato–maize intercrop produced the lowest fruit weights and marketable yield in 2004 and 2006, while yield of onion, kale and maize in intercrops were not significantly different from their monocrops. Land equivalent ratio was >1 in all the cropping systems.     

Responses of photosynthetic rates and yield/quality of main crops to irrigation and manure application in the black soil area of Northeast China

Soil nutrients and water have long been recognized as the main determining factors influencing agricultural productivity in rain-fed agriculture. Manure application and irrigation can increase crop yield when nutrients and water are deficient. Often effects of water and nutrients are closely related and can not be easily separated in actual production. Three years of experiment were conducted in northern part of black soil area of Northeast China to investigate the responses of photosynthetic rates and yield/quality of main crops, wheat (Triticum aestivum L.), maize (May zeas L.), soybean (Glycine max L. Merr.) to irrigation and manure application. Irrigation and manure application had no effects on photosynthetic patterns during reproductive development in crops, maximum photosynthetic rates were achieved by irrigation, and manure application maintained relatively higher photosynthetic rates after the peak. On average, higher photosynthetic rates with irrigation may contribute to higher yield in soybean but not in maize and wheat. Responses of crop yield and quality to manure application and irrigation varied in the crops. Soybean yield and quality was very sensitive to irrigation and manure application. The greater supply of nutrients with sufficient water, the higher the yield. However, the high-yield of soybean achieved was accompanied with a decline of seed protein content. Maize yield mainly depended on nutrients used not the water supply, irrigation resulted in higher water content in the seed of maize and lower grain protein content in wheat at harvest, which is detrimental to seed storage in maize and processing quality in wheat. In the northern part of black soil area in Northeast China, the management of manure is critical to improve crop production, the optimum management for maize and wheat production was to apply chemical fertilizer and manure without irrigation, but for soybean was to apply fertilizer and manure with irrigation.     

Integrated response of intercropped maize and potatoes to heterogeneous nutrients and crop neighbours

Background and Aims

In communities, plants often simultaneously interact with intra- and inter-specific neighbours and heterogeneous nutrients. How plants respond under these conditions and then affect the structure and function of communities remain important questions.

Methods

Maize (Zea mays L.) was intercropped with potatoes (Solanum tuberosum L.). In the field experiment, we applied fertilizer both homogeneously and heterogeneously under monocropping and intercropping conditions. The heterogeneous nutrient treatment in intercropping was designed with different fertilizer placements, at intraspecific and interspecific rows, respectively. In the pot experiment, crops were grown under both homogeneous and heterogeneous nitrogen conditions with single plant, intraspecific and interspecific competition. Shoot and root biomass and yield were measured to analyse crop performance.

Results

In the field experiment, the heterogeneous nitrogen, compared with the homogenous one, enhanced the performance of the intercropped crop. Importantly, this effect of heterogeneous nitrogen was greater when fertilizer was applied at interspecific rows, rather than at intraspecific rows. Moreover, in pot experiments, the root foraging precision of the two crops was increased by interspecific neighbours, but only that of potatoes was increased by intraspecific neighbours.

Conclusions

The integrated responses of plants to heterogeneous neighbours and nutrients depend on the position of nutrient-rich patches, which deepen our understanding of the function of plant diversity, and show that fertilizer placement within multi-cropping systems merits more attention. Moreover, the enhanced utilization of heterogeneous nitrogen could drive overyielding in multi-cropping systems.     

Nitrogen economy in relay intercropping systems of wheat and cotton

Relay intercropping of wheat and cotton is practiced on a large scale in China. Winter wheat is thereby grown as a food crop from November to June and cotton as a cash crop from April to October. The crops overlap in time, growing as an intercrop, from April till June. High levels of nitrogen are applied. In this study, we analyzed the N-economy of the monocultures of cotton and wheat, and of four relay intercropping systems, differing in number of rows per strip of cotton or wheat. Field experiments were carried out from 2001/02 to 2003/04 in the Yellow River region in China. We quantified the nitrogen uptake and nitrogen use efficiency of wheat and cotton in relay intercropping systems to test if intercrops are more resource use efficient in comparison to monocrops. Nitrogen (N) yields of wheat per unit area in the four intercropping systems were lower than in the monocrop, which ranged from 203 to 288 kg ha⁻¹. The total N-uptake per unit biomass was similar between wheat in mono- and intercrops. On average, the N-yield of cotton per unit area was lower in intercrops than in monocrops, which ranged from 110 to 127 kg ha⁻¹, but the total N-uptake per unit biomass was higher in intercropped cotton, as dry matter production was reduced to a greater extent by intercropping than N-uptake. The N-uptake of cotton was diminished during the intercropping phase, but recovered partially during later growth stages. The physiological nitrogen use efficiency (IE) of wheat was not much affected by intercropping, but it was reduced in cotton, due to delayed flowering and less reproductive growth. Total N-efficiency of the system was assessed by comparing the relative nitrogen yield total (RNT), i.e. the sum of the ratio’s of total N-uptake by a component crop in the intercrop relative to the N-uptake in the monocrop, to the relative yield total. RNT ranged from 1.4 to 1.7, while the relative yield total (RYT) ranged from 1.3 to 1.4, indicating that intercrops used more nitrogen per unit production than monocrops. An analysis of the crop nitrogen balance showed that the nitrogen surplus of sole crops amounted to 220 kg ha⁻¹ for wheat and 140 kg ha⁻¹ for cotton, while in the intercropping systems, the annual N surplus exceeded 400 kg ha⁻¹. Conventional N-management in intercrops thus results in high N-surpluses that pose an environmental risk. The N management could be improved by means of a demand-based rate and timing of N applications.     

Using competitive and facilitative interactions in intercropping systems enhances crop productivity and nutrient-use efficiency

This paper reviews recent research on the processes involved in the yield advantage in wheat (Triticum aestivum L.)/maize (Zea mays L.), wheat/soybean [Glycine max (L.) Merr.], faba bean (Vicia faba L.)/maize, peanut (Arachis hypogaea L.)/maize and water convolvulus (Ipomoea aquatica Forsk.)/maize intercropping. In wheat/maize and wheat/soybean intercropping systems, a significant yield increase of intercropped wheat over sole wheat was observed, which resulted from positive effects of the border row and inner rows of intercropped wheat. The border row effect was due to interspecific competition for nutrients as wheat had a higher competitive ability than either maize or soybean had. There was also compensatory growth, or a recovery process, of subordinate species such as maize and soybean, offsetting the impairment of early growth of the subordinate species. Finally, both dominant and subordinate species in intercropping obtain higher yields than that in corresponding sole wheat, maize or soybean. We summarized these processes as the `competition-recovery production principle'. We observed interspecific facilitation, where maize improves iron nutrition in intercropped peanut, faba bean enhances nitrogen and phosphorus uptake by intercropped maize, and chickpea facilitates P uptake by associated wheat from phytate-P. Furthermore, intercropping reduced the nitrate content in the soil profile as intercropping uses soil nutrients more efficiently than sole cropping.     

Evaluation of maize/pepper intercropping model in the management of pepper veinal mottle virus,genus Potyvirus,family Potyviridae on cultivated pepper (Capsicum annuum L.) in Nigeria

Three pepper cultivars obtained from National Horticultural Research Institute (NIHORT) Idi-Ishin, Ibadan were intercropped with maize for two planting seasons between March and September in each year. These pepper cultivars were NHV1-D96, and NHV1-E96 and NHV1-F96. A 90-day maturing maize variety (DMSR-1) was used as the intercropping companion plant. The pepper seedlings were raised in a greenhouse. A randomised complete block design was used for this experiment. Each variety was intercropped with maize and replicated three times including the sole plot. The results obtained for each year were not significantly different from each other. There was a significant difference in pepper veinal mottle virus (PVMV) disease incidence and severity at a probability of less than 5% in the treatment used. PVMV disease incidence and severity was relatively higher in the sole pepper crop compared with pepper intercropped with maize. In the three varieties of peppers intercropped with maize, less than 17% disease incidence and 15% disease severity were recorded in all the varieties with a minimum yield of 4 tons per hectare compared with the sole pepper cropping of the same variety that recorded as high as 75% disease incidence and 72% disease severity with a maximum yield of 3.3 tons per hectare. There was a significant negative correlation at probability less than 0.05 between disease incidence, severity and the fruit yield of pepper. Variety NHV1-F96 in the maize intercrop recorded the highest yield of 15.99 tons/ha with a land equivalent ratio of 2.4 tons/ha. The success of the PVMV disease management evaluated in this study was judged by the extent of reduction in number of diseased plants and by an increase in vigor of the cultivated pepper crop, with an increase in fruit yield and quality. This signifies that for devising effective viral disease management for any crop it is important that the vectors of the virus present in the particular area are exactly controlled from having contact with the target plant. The reduction of pest incidence with intercropping of non-host plants should be carefully considered.     

Intercropping Competition between Apple Trees and Crops in Agroforestry Systems on the Loess Plateau of China

Agroforestry has been widely practiced in the Loess Plateau region of China because of its prominent effects in reducing soil and water losses, improving land-use efficiency and increasing economic returns. However, the agroforestry practices may lead to competition between crops and trees for underground soil moisture and nutrients, and the trees on the canopy layer may also lead to shortage of light for crops. In order to minimize interspecific competition and maximize the benefits of tree-based intercropping systems, we studied photosynthesis, growth and yield of soybean (Glycine max L. Merr.) and peanut (Arachis hypogaea L.) by measuring photosynthetically active radiation, net photosynthetic rate, soil moisture and soil nutrients in a plantation of apple (Malus pumila M.) at a spacing of 4 m × 5 m on the Loess Plateau of China. The results showed that for both intercropping systems in the study region, soil moisture was the primary factor affecting the crop yields followed by light. Deficiency of the soil nutrients also had a significant impact on crop yields. Compared with soybean, peanut was more suitable for intercropping with apple trees to obtain economic benefits in the region. We concluded that apple-soybean and apple-peanut intercropping systems can be practical and beneficial in the region. However, the distance between crops and tree rows should be adjusted to minimize interspecies competition. Agronomic measures such as regular canopy pruning, root barriers, additional irrigation and fertilization also should be applied in the intercropping systems.     

Intercropping drives plant phenotypic plasticity and changes in functional trait space

The relevance of intercropping, where two or more crop species are simultaneously grown on the same land space, is growing due to its potential for improving resource use and maintaining stable yields under variable weather conditions. However, the actual growth of intercropped species may differ resulting from the idiosyncratic effect of crop diversity, and with this, the realized benefits from intercrops are found to depend critically on the cultivar, species, management and environmental conditions. This study aimed to apply a trait-based approach, in which ecological niche spaces are defined through n-dimensional hypervolumes, to identify the contribution of species/cultivar, cultivation design (sole crop or intercrop) and management (low or high fertilization) to the trait diversity of four crop species, pea-barley and faba bean-wheat, when grown as sole crops and intercrops. Four traits were used as trait axes for the trait space analysis: canopy height, shoot biomass, tiller/node number, and grain yield. We found that trait spaces differed with crop species and cultivars, and whether they were grown as intercrops or sole crops. Trait spaces differed between high and low fertilization only for the cereals grown in the more productive site (i.e. Denmark). Species grown as intercrops had larger volumes than when grown as sole crops, as a result of trait plasticity. This response to intercropping was apparent in almost all the species grown in Sweden and Denmark, except for wheat in Denmark. The study demonstrated that individual species responded to intercropping compared to sole cropping through the plasticity of traits, which influenced the shape of the hypervolumes to divide up the trait space between the species. The findings are important in illustrating the plastic responses of arable crops, which are relevant for understanding the productivity of species grown in intercrops as compared to sole crops.     

玉米与籽粒苋不同种植模式下植物生长及Cd累积特征

为实现Cd污染农田边生产边修复的目标,采用田间原位修复的方式,将玉米与籽粒苋在Cd污染农田中以5种不同的间作模式种植: 交替宽窄行玉米宽行间作单行籽粒苋(T₁)、交替宽窄行玉米宽行间作双行籽粒苋(T₂)、等行距双行玉米间作单行籽粒苋(T₃)、等行距双行玉米间作双行籽粒苋(T₄)、玉米/籽粒苋等4行距间作(T₅),并以玉米(CK₁)和籽粒苋(CK₂)单作种植作为对照,探究不同间作结构配置对作物与超富集植物生长及Cd累积特征的影响.结果表明: 1)与CK₁相比,各间作模式单株玉米的籽粒产量呈增加趋势;T₁间作模式玉米的籽粒产量较CK₁增加10.5%,T₄和T₅间作模式玉米的籽粒产量较CK₁分别减少6.3%和5.4%,T₂和T₃间作模式基本稳产;间作籽粒苋地上部单株生物量及单位面积产量较CK₂分别显著减少69.5%～95.7%和83.9%～96.9%. 2)各间作模式玉米籽粒Cd含量较CK₁呈减少趋势,而间作籽粒苋Cd含量较CK₂呈增加趋势. 3)与CK₂相比,各间作模式籽粒苋的富集系数、转运系数、有效转运系数均呈增加趋势;间作籽粒苋地上部Cd的单株及单位面积提取量较CK₂分别显著减少40.4%～86.7%和70.4%～88.9%;各间作模式玉米与籽粒苋地上部Cd的单位面积提取总量高于单作玉米,但低于单作籽粒苋. 4)各间作模式玉米根际土有效态Cd含量及籽粒苋根际土总Cd、有效态Cd含量分别较单作玉米及单作籽粒苋呈增加趋势,但对非根际土没有显著影响.本研究中,T₁间作模式有利于玉米籽粒产量的提高,T₅间作模式有利于籽粒苋Cd提取量的最大化.