The response of cassava (Manihot esculenta) to spatial arrangement and to soybean intercrop

Response of cassava to row spacing and plant population density (0.62 plants m⁻² in 180-cm rows; 1.23 plants m⁻² in 90-, 180-, 270-, and 270- plus 90-cm (i.e. paired rows); and 2.46 plants m⁻² in 90- and 180-cm rows), and to soybean intercrop at two row spacings of cassava (90 and 270 cm) was studied at a high latitude (27°S) in south-east Queensland, Australia, where low temperature limits a growing season to 9 months. Detailed observations were made in sole crops on leaf canopy structure and light penetration in the three row spacings at the medium density to allow an estimation of light availability for an intercrop between cassava rows.The low plant density or the 270-cm row plants produced the lowest total dry matter and tuber yield at harvest, while the two higher densities or the two narrower rows produced similar total and tuber dry weight. Intercropped cassava produced a similar tuber yield to the sole crop at the corresponding spatial arrangement, but total dry matter was lower in the former.Leaf area index was similar among the 90-, 180- and 270-cm row spacings in sole crops throughout the growth period. However, leaf area was unevenly distributed horizontally for a longer time as row spacing increased. This resulted in light penetrating the inter-row space for a longer period in wider rows in sole crops, more than 50% full sunlight reaching soil level for 90, 120 and 130 days after planting in the 90-, 180- and 270-cm rows, respectively. This light environment would be available for an intercrop if cassava growth is not affected by the intercrop. The results for cassava intercropped with soybean show that in fact cassava growth was reduced by the associated soybean, and hence light available for the soybean growth would have been more than that estimated above.     

Wheat/maize or wheat/soybean strip intercropping: II. Recovery or compensation of maize and soybean after wheat harvesting

While early-maturing crops benefit from intercropping, late-maturing crops usually suffer growth penalties during the intercropping phase. It is possible, however, that recovery or compensation of the late-maturing crops occurs after the harvest of the early-maturing crops. Three field experiments were conducted at Baiyun in 1997 and at Jingtan in 1997 and 1998 to test the hypothesis in wheat/maize and wheat/soybean intercropping. The biomass and nutrient accumulation in intercropped soybean were significantly smaller than in sole soybean before wheat harvest but thereafter increased sharply at Jingtan site in 1997. The rates of dry matter accumulation in the intercropped maize (10.0–20.1 g/m² per day) were significantly lower than those in the sole maize (17.1–34.8 g/m² per day) during the early stage from 7 May to 3 August, while mostly intercropped with wheat. After 3 August, however, the rates of intercropped maize, increasing to 58.9–69.9 g/m² per day, was significantly greater than in sole maize (22.7–51.8 g/m² per day) at Baiyun site in 1997 and nutrient acquisition showed the same trends as growth. At Jingtan site in 1998, the disadvantage of the border row of intercropped maize resulted from interspecific competition diminished after wheat harvest and disappeared at maize maturity. It was concluded that there was indeed recovery of growth after wheat harvesting in wheat/maize and wheat/soybean intercropping. However, the recovery was limited under N₀P₀ treatment. The interspecific competition, facilitation and recovery are together contributed to yield advantage of intercropping.     

Intercropping of cassava (Manihot esculenta) with maize or cowpea under different row arrangements

The effects of various intercropping arrangements of cassava (Manihot esculenta Crantz) and maize (Zea mays L.) or cowpeas (Vigna unguiculata L. Walp) on crop yields were compared over a 3-year period in Nigeria, in an attempt to improve grain yields of the maize and cowpea intercrops without substantially reducing the cassava root yield. Sole-cropped cassava produced the largest yield; this was significantly reduced by about 40% when intercropped with maize or cowpeas but only when using a 1:2 (cassava:intercrop) row arrangement, mainly because of a reduction in its population density. Cassava yield differences among different row arrangements were more marked when grown with maize than with cowpeas. Maize and cowpea grain yields were reduced by intercropping, but somewhat less so when grown with cassava in widely spaced rows. Cassava row spacing did not affect maize yield, but cowpea yield was affected significantly. Land Equivalent Ratios were always greater than 1, irrespective of the crop combinations and row arrangements. However, increased yields of intercropped cassava:maize were obtained at 1:1 or 2:2 row arrangements and of cassava:cowpea at 2:2 rows, without much reduction in cassava tuber yield.     

木薯间作糯玉米的高产高效模式分析

为研究不同栽种规格的木薯间作糯玉米模式和发掘高产高效间作模式,对木薯净作,糯玉米净作和8种木薯间作糯玉米模式进行了鲜薯产量和经济效益的研究。结果表明：木薯间作糯玉米模式是可行的,体现出明显的间作优势。发现不同间作模式的经济效益不同,其中处理9(大行距100 cm,小行距70 cm)的鲜薯产量(51 274.36 kg/hm2)最高,处理4(行距100 cm)的经济效益(52 794.15元/hm2)最高,处理9的经济效益(46 556.97元/hm2)排第3位。综合评价认为,处理9的木薯间作糯玉米模式最合理。试验结果为进一步推广高产高效木薯间作糯玉米模式提供了有力依据。     

Performance of double cropping and relay intercropping for black soybean production in small-scale farms

We investigated the soybean productivity of double cropping and relay intercropping in farmer’s fields for three years using two black soybean cultivars of Kurozukin and Tanbaguro, which are used for the first and second crop, respectively. Kurozukin is the early maturing cultivar for vegetable soybean harvest and Tanbaguro is the late-maturing cultivar for the harvest of vegetable soybean and seeds. The yield of the first crop (Kurozukin) was similar to the mono cropping regardless of cropping patterns. However, the yield of the second crop (Tanbaguro) was affected by cropping patterns. The yield of Tanbaguro in double cropping was prone to decrease by late sowing. The late sowing was induced by the late sowing and late harvesting of Kurozukin because of the low temperature in April and the large amount of precipitation in rainy season, respectively. In relay intercropping that Tanbaguro was sown between the rows of Kurozukin at about one month before the harvest of Kurozukin, the yield of Tanbaguro was similar to the mono cropping and the competition with Kurozukin was not observed. Thus, the land equivalent ratio value of double cropping was lower than that of relay intercropping. These results suggest that relay intercropping is more useful cultivation system than double cropping to increase the annual soybean production.     

Land Equivalent Ratio of Groundnut-Fingermillet Intercrops as Affected by Plant Combination Ratio,and Nitrogen and Water Availability

Abstract

Field experiments were conducted to characterize intercropping advantages in groundnut-fingermillet intercrop in relation to crop combination ratios, soil moisture and nitrogen (N) availability. Three intercrops in 1 : 2, 1 : 1 and 2 : 1 alternating rows of groundnut and fingermillet were examined for their growth and yield in comparison with their respective sole crops in 1996. The effect of well watered (W) and water stressed (D) conditions on the intercropping advantage was also examined for 1 : 1 intercrops in 1995 and 1996. Fertilizer N was applied at the rate of 20 kg ha^?1 in 1995 and 50 kg ha^?1 in 1996. The total above-ground biomass (DM) and its land equivalent ratio (LER) were highest in the 1 : 1 combination ratio. The DM production of intercropped fingermillet was higher in 1996 with higher N than in 1995 with low N application, while those of groundnut were similar in both years. The intercropped groundnut exhibited significantly higher DM production after the fingermillet harvest. The LERs in grain yield were higher in 1996 (1.43 under W and 1.45 under D), than in 1995 (0.87 under W and 1.22 under D). Also, LERs were consistently higher under D than W conditions. Water stress severely reduced the leaf area index (LAI) of fingermillet at a low N, especially in the later stages, whereas higher N alleviated the water stress effect. A close linear relationship was observed between LAI and leaf area (LA) per unit leaf N both for groundnut and fingermillet, with intercrops producing larger LA per unit leaf N than sole crops. Intercropping maintained higher ability in leaf net photosynthesis and transpiration of groundnut up to later stages, and significantly reduced water evaporation from the soil surface under the canopy than sole cropping of fingermillet. These results suggest that three processes associated with the intercropping yield advantages in the groundnut-fingermillet intercrop; 1) higher leaf photosynthesis and vigorous growth of groundnut after the fingermillet harvest, 2) higher LA production per unit N and 3) efficient water use. In conclusion, interspecific shading was considered to be the key mechanism associated with these processes, leading to the intercropping advantages. The degree of the interspecific shade and its effect on growth and yield depended on the available soil N and water.     

Intercropping with banana to improve fractional interception and radiation-use efficiency of immature rubber plantations

Intercropping provides an important means of raising not only productivity and land-use efficiency of smallholder rubber lands, but also income generation during the unproductive immature phase of the rubber tree. To evaluate current recommendations for intercropping rubber in Sri Lanka, we assessed the effects of a range of planting densities of banana, the most common companion crop of rubber on productivity and resource capture. In this paper, we test the hypothesis that rubber/banana intercropping, even at high densities of banana, results in an increase in biomass per unit land area and per crop plant due to an increase in both radiation capture and radiation-use efficiency. Five treatments were imposed: sole crop rubber (R); sole crop banana (B) and three intercrop treatments comprising an additive series of one (BR), two (BBR) and three (BBBR) rows of banana to one row of rubber. Dry matter production in the rubber-based treatments was directly related to planting density, being least in the sole rubber and greatest in BBBR intercrop. A more than four-fold increase in dry matter across treatments derived from an increase not only in light capture (270%) but also radiation-use efficiency (RUE, 230%). Neither R nor BR treatment, which is currently recommended for intercropping in Sri Lanka, achieved full ground cover with fractional interception remaining below 40 and 50%, respectively. Fractional interception was greatest in BBBR treatment and by the end of the measurement period, total intercepted radiation was 23 and 73% greater than that in the BBR and BR intercrops, respectively. Shade did not limit either photosynthesis or growth of component crops in the intercrops, even when planting density of banana was increased three-fold. In fact, intercropping increased growth of both rubber and banana components suggesting that shade associated with the denser intercrop canopies, moderated the microclimate and alleviated plant stress. These results highlight the potential gains that can be made by intercropping and optimising planting density for improved resource capture in immature rubber plantations.     

Comparisons of radiation use efficiency of mono-/inter-cropping systems with different row orientations

Intercropping may be helpful to solve future food problem in developing countries. The aim of this study was to compare production efficiency in intercropping with sole cropping in terms of radiant energy use. For analysing crop radiation capture and utilisation, three indices are often used: the fraction of radiation intercepted (F), radiation use efficiency (RUE) and harvest index (HI). Using those indices, maize–bean intercropping was evaluated and compared with maize and bean sole cropping systems. The findings were as follows: the intercrop F was higher than the sole crop F, the sole maize RUE was higher than the others, and there was no difference in HI among cropping systems. From those results, the intercropping may be equivalent to maize sole cropping in the overall efficiency of radiation interception and use. Therefore, when it is considered that both maize and beans would be planted in a given area of land, intercropping has more efficient radiation harvests than sole cropping. No effect of row orientation was found on F, RUE and HI.     

薯-豆套作模式下作物对种间竞争与补偿作用的响应

以马铃薯-大豆套作模式为研究对象,通过2年的大田试验,分析不同熟期大豆品种与马铃薯组合后系统内作物干物质和养分积累的特性与种间竞争补偿的相互关系,阐明间套作系统种间竞争力弱化和恢复补偿能力提高的作用机理,为实现间套作可持续发展提供科学依据。结果表明:套作马铃薯干物质及养分积累无显著变化,而套作大豆变化显著。出苗60 d内套作大豆干物质积累量是同期单作的43.74%,出苗后80～100 d,晚熟品种干物质积累量相对于中熟和早熟提高的幅度分别为35.54%～59.22%和65.56%～70.81%,大豆收获时,晚熟品种干物质积累接近单作,两者间差异不显著。共生期,套作大豆N、P、K积累量较同期单作降低的幅度分别为31.43%～41.44%、21.17%～25.36%和23.23%～35.6%,晚熟品种与中熟、早熟品种间差异达到显著水平。共生期结束后,套作大豆养分吸收量较单作显著增加,收获时,晚熟品种N、P、K养分积累量接近单作,两者间差异不显著。综上,在该群体中,马铃薯是核心作物,共生期处于竞争优势(A_PS>0、CR_PS>0),而大豆处于竞争弱势(A_PS<0、CR_PS<0),选择晚熟大豆品种与马铃薯组合可弱化种间竞争力和营养竞争比率,还有利于马铃薯收获后恢复补偿能力的发挥。     

The growth and yield of rubber at maturity is improved by intercropping with banana during the early stage of rubber cultivation

Intercropping with short-term crops provides a significant additional income during the long immature period of rubber tree growth when no latex is produced. Much previous evidence has demonstrated that the growth of young rubber trees is unaffected by the presence of an intercrop. However, few, if any studies have however been conducted to date to assess the effects of intercropping on subsequent growth and yield of rubber once the companion intercrop is removed. This study demonstrates for the first time that intensive intercropping of young rubber with banana may result not only in a sustained increase in growth and yield of rubber trees but also a reduction in the length of the unproductive immature phase.Rubber was grown either as a sole crop, or intercropped for the first 4 years with banana. The intercrop comprised an additive series of one, two or three rows of banana to one row of rubber. Growth of rubber was monitored for 6 years, i.e. up to the time that tapping for latex began and a logistic growth function was fitted to girth data in order to assess growth. Intercropping had a positive effect on the growth of rubber throughout the 6 years of the study, with the result that trees in the intercrop treatment were ready for tapping 4 months earlier than in the sole crop. Whilst girth and height were greater in the intercrops, bark thickness was similar to that of the sole crop. Intercrop treatments had no effect on latex yield per plant, but yield per hectare was greater in the intercrop than sole crop treatments due to a higher number of tappable trees.     

Evaluating pea and barley cultivars for complementarity in intercropping at different levels of soil N availability

Two field experiments were carried out on a temperate sandy loam using six pea (Pisum sativum L.) and five spring barley (Hordeum vulgare L.) cultivars to determine cultivar complementarity in the intercrop for grain yield, dry matter production and nitrogen (N) acquisition. Crops were grown with or without the supply of 40 or 50 kg N ha⁻¹ in the two experiments. Cultivars were grown as sole crops (SC) and as mixed intercrops (IC) using a replacement design (50:50). The land equivalent ratio (LER), which is defined as the relative land area under SC that is required to produce the yields achieved in intercropping, were used to compare cultivar performance in intercropping relative to sole cropping.Barley was the stronger competitor in the intercrops and as a result barley grain yield and nitrogen uptake in IC were similar to SC. The per plant pea grain production and aboveground N accumulation in IC were reduced to less than half compared to SC pea plants due to competitive interactions.Application of N caused a dynamic change in the intercrop composition. Competition from barley increased with N application and the pea contribution to the combined intercrop grain yield decreased. The LER values showed that in the intercrop plant growth resources were used on average 20% more efficient without N application and 5–10% more efficient with N application.The choice of pea cultivar in the intercrop influenced the intercrop performance to a larger degree than the choice of barley cultivar. Furthermore, pea cultivar×cropping systems interactions was observed, indicating that cultivars performed differently in sole and intercrops. An indeterminate pea cultivar competed strongly with barley causing a greater proportion of peas in the intercrop yield, but caused a reduced N uptake and yield of barley. Determinate peas with normal leaves caused the highest degree of complementary use of N sources by allowing barley to exploit the soil N sources efficiently, while they contribute with fixed N₂. However, difference in performance among cultivars was observed. Using the indeterminate pea cultivar combined IC grain yield was in general lower than the greatest sole crop yield and vice versa for the determinate pea cultivars. Up to 22% (LER=1.22) greater combined IC grain yield was observed in several mixtures using determinate pea cultivars.From the present study, it is was concluded that there is a need for breeding suitable pea cultivars for intercropping purposes, since cultivars bred for sole cropping may not be the types, which are the most suitable for intercropping. For optimized N-use in pea–barley intercrops it is concluded that important traits for the intercropped pea are: (1) determinate growth, (2) a medium competitive root system for soil inorganic N and other nutrients during early growth, (3) high light absorption capacity by peas growing underneath the canopy of the higher barley component and (4) early establishment of symbiotic N₂ fixation to support a high growth rate during early growth stages.Fertilized pea–barley intercrops gave a 15% higher net income than fertilized barley sole cropping and is regarded as a better safeguard for the farmer’s earnings compared to pea sole cropping known for variable yields and poor competitive ability towards weeds.     

Intercropping in a temperate environment for irrigated fodder production

Fodder crops such as maize and oats are very productive under irrigation in a temperature environment; however, their protein content is too low for rapidly growing or lactating animals. Intercropping with legumes could help overcome this protein limitation.Dry matter (DM) production, protein content and total protein yield were measured in a range of intercropping combinations. For summer fodder production, maize (Zea mays L.) was intercropped with lablab bean (Lablab purpureus L.) or soybean [Glycine max (L.) Merr.]. For winter production, oat (Avena sativa) was intercropped with field pea (Pisum sativum).Alternative-row maize-plus-soybean was the most promising intercrop combination. Averaged over two years, the intercrop yield was 14.1 t¹/ha compared with a sole maize yield of 17.5 t/ha, while protein contents were 93 and 71 g/kg. In one of the two years protein production per unit area of the intercrop was significantly greater than that of sole maize.Intercropping with lablab bean planted in the same rows as maize increased protein content by approximately 10 g/kg. Reducing the maize population to one third of normal (2.4 vs 7.2 plants/m²) decreased maize yield and increased lablab bean production in one year but had no effect in the next year. Intercropping with soybeans in the same row as maize was less effective than with lablab bean.The oat-with-pea intercrops were similar to maize-with-lablab bean in raising the protein content about 10 g/kg. None of the planting patterns used reduced the dominance of the oats to a level where the peas contributed more than 10% of the total DM.     

Increased productivity through integrated soil fertility management in cassava–legume intercropping systems in the highlands of Sud-Kivu,DR Congo

Smallholder farmers in sub-Saharan Africa are confronted by low productivity and limited investment capacity in nutrient inputs. Integrated soil fertility management (ISFM) aims at increased productivity through the combined use of improved germplasm, judicious fertilizer application and organic matter management, adapted to the local farming conditions. We hypothesize that the application of these different ISFM components can result in significant increases in productivity and economic benefits of cassava–legume intercropping systems. Participatory demonstration trials were conducted in the highlands of Sud-Kivu, DR Congo with 12 farmer groups during 3 seasons. Treatments included the farmers’ common practice (local common bean and cassava varieties, seed broadcast and manure addition) and sequentially added ISFM components: improved bean and cassava germplasm, modified crop arrangements, compound NPK fertilizer application and alternative legume species (groundnut or soybean). The use of improved germplasm did not result in yield increases without simultaneous implementation of other ISFM components. Modifying the crop arrangement by planting cassava at 2 m between rows and 0.5 m within the row, intercropped with four legume lines, increased bean yields during the first season and permits a second bean intercrop, which can increase total legume production by up to 1 t ha⁻¹ and result in an additional revenue of almost 1000 USD ha⁻¹. Crop arrangement or a second legume intercrop did not affect cassava storage root yields. Fertilizer application increased both legume and cassava yield, and net revenue by 400–700 USD ha⁻¹ with a marginal rate of return of 1.6–2.7. Replacing the common bean intercrop by groundnut increased net revenue by 200–400 USD ha⁻¹ partly because of the higher market value of the grains, but mostly due to a positive effect on cassava storage root yield. Soybean affected cassava yields negatively because of its high biomass production and long maturity period; modifications are needed to integrate a soybean intercrop into the system. The findings demonstrate the large potential of ISFM to increase productivity in cassava–legume systems in the Central-African highlands. Benefits were, however, not observed in all study sites. In poor soils, productivity increases were variable or absent, and soil amendments are required. A better understanding of the conditions under which positive effects occur can enable better targeting and local adaptation of the technologies.     

早熟菜用大豆农艺性状、籽粒产量和品质形成规律的研究

采用早熟菜用大豆品种为试材,对不同菜用大豆品种农艺性状、籽粒产量和品质的形成规律进行了研究.结果表明:早熟菜用大豆品种株型矮小,分枝少,节问长度较短;一粒荚、二粒荚所占的比例较大,百粒重和收获指数均较高;不同生育期品种间光合速率、蒸腾速率和气孔导度没有显著差异;在籽粒形成过程中,可溶性糖含量和脂肪含量均呈上升趋势,品种间蛋白质含量和蛋脂总含量积累有所差异.综合籽粒产量和品质性状,沈农引48是更适合选用的早熟菜用大豆品种.     

Effect of narrow-row planting patterns on crop competitive and economic advantage in maize–soybean relay strip intercropping system

Narrow-row planting patterns directly affect crop yield and competition in intercropping systems. A two-year (2012 and 2013) field experiment was conducted to determine the interactive behavior between intercrops in a maize–soybean relay strip intercropping system. Maize plants were planted in different narrow-wide row planting patterns, whereas soybean was planted in wide rows. The total biomass and grain yield of maize increased with increasing maize narrow-row spacing, but the opposite trend was observed for soybean. The aggressivity, competitive ratio, and partial relative crowding advantage values for maize were greater than those for soybean. Moreover, the competitive interaction of the intercrops was affected by the distance between maize and soybean rows. The highest intercrop land equivalent ratio (LER) 1.61 and 1.59 was found in the 40:160 planting pattern (i.e. 40 cm narrow-row spacing and 160 cm wide-row spacing of maize) during 2012 and 2013, respectively. Combined with actual yield loss and LER, the intense intra-specific competition of maize plants reduced the depression for the associated soybeans when the maize narrow-row spacing was less than 30 cm. When the narrow-row spacing was wider than 50 cm, soybean growth was seriously depressed by maize because of the stronger inter-specific competition between maize and soybean. The maximum yield and economic advantage appeared in the 40:160 narrow-wide row planting pattern. Therefore, intercropping advantage may be achieved by changing the row spacing and distance between intercrop rows to coordinate the inter-specific competition between maize and soybean.     

Effects of crop density and tillage system on grain yield and N uptake from soil and atmosphere of sole and intercropped pea and oat

Pea (Pisum sativum L.) and oat (Avena sativa L.) were grown as sole and mixed crops in various densities under two different tillage systems on a loess soil near Göttingen/Germany in a 2-year field experiment (2002/2003). In the conventional tillage system a mouldboard plough (CT) was used and in the minimum tillage system a rotary harrow (MT) was employed. The effect of crop density and tillage system on the grain dry matter and grain N yields, N₂ fixation and soil N uptake were determined to address the following questions: (i) which mixture compositions exhibit the highest grain yields compared to the sole crops, (ii) which mixture compositions also fix a high level of N₂ and leave low levels of residual inorganic soil N after harvest, and (iii) whether the intercrop advantage is influenced by the tillage system. For (i) the result in 2002 showed that the highest grain yields of both sole cropped pea and oat and intercropped pea and oat were achieved at the highest densities. In 2003, when the inorganic soil N content was higher and weather conditions were warmer and drier, grain yields were significantly higher than in 2002, but sole as well as intercropped pea and oat gave their highest grain yields at lower densities. For both years and tillage systems, the highest intercrop advantages were achieved in mixtures with densities above the optimal sole crop densities. The result for (ii) was that a distinctly higher proportion of nitrogen was derived from the atmosphere (Ndfa) by intercropped pea than by sole cropped pea. However, the uptake of soil N by intercropped pea and oat was not reduced in comparison with that of sole cropped oat as the decrease in the uptake of N from the soil by oat at lower oat densities in the mixture was compensated for by the soil N uptake of pea. Additionally, the N_min-N content of the soil following the mixtures and sole cropped oat did not differ, especially in the deeper soil layers because oat in mixture was forced to take up more soil N from deeper layers. Therefore, the risk of soil N losses through leaching after mixtures was lower compared to sole cropped pea. The tillage system (iii) had no significant influence on grain yield and soil N uptake, but N₂ fixation and the competitive ability of intercropped pea were higher under CT than with MT. An additional result was that intercropping led to a significantly increased grain N content of both pea and oat compared to the sole crops. The increase in grain N content from sole to intercrop was from 3.30 to 3.42% for pea and from 1.73 to 1.96% for oat as a mean for both years and tillage systems. The present study confirms that growing pea and oat as intercrops highlights potential economic and environmental benefits which still need to be understood in more detail in order to exploit intercropping to a greater extent.     

Yield and land-use efficiency of a cassava/cowpea intercropping system grown at different phosphorus rates

Cassava (Manihot esculenta Crantz) is frequently intercropped with cowpea [Vigna unguiculata (L.) Walp subsp. unguiculata] in the tropics. Little is known about the influence of P fertilization practices on the efficiency of land use and yields in cassava/cowpea intercropping systems. Two experiments were conducted on a Typic Dystropept soil with the objective of determining the influence of P application rate on yield and P status of cassava and cowpea grown in sole and intercropping systems, and the influence on land use efficiency. Cassava yields averaged across P rates were reduced 29% from the 28 Mg ha⁻¹ sole crop yield when intercropped with cowpea in 1979–1980. Cowpea yields were reduced by 19–38% from a sole crop yield of 1522 kg ha⁻¹ when intercropped in 1979, and 29–38% from a sole crop yield of 1277 kg ha⁻¹ in 1980. The rate of P application had little influence on cassava yield, except in 1981 when intercropped cassava yields were greater than 40 Mg ha⁻¹. In 1981, increasing the rate of P application from 0 to 44 kg ha⁻¹ resulted in a cassava yield increase from 41 to 47 Mg ha⁻¹. In 1979 and 1980, increasing the rate of P application from 0 to 22 kg ha⁻¹ increased cowpea yield 44 and 92%, respectively, while increasing P rate from 66 to 132 kg ha⁻¹ increased cowpea yield 28 and 18%, respectively. In 1981 and 1982, increasing the rate of P application from 0 to 44 kg ha⁻¹ increased cowpea yield by 1052 kg ha⁻¹. Phosphorus concentration of cassava and cowpea leaf blades increased with increases in rate of P application from 66 to 132 kg ha⁻¹ in 1979 and 1980, and from 0 to 44 kg ha⁻¹ in 1981 and 1982. Intercropping cassava with cowpea resulted in a 30% increase in land-use efficiency when no P was applied, while land-use efficiencies resulting from intercropping were increased by 41–50% with P application rates of 22–132 kg ha⁻¹. Cassava proved to be well-adapted to low-P soils and very competitive even without P application, whereas cowpea required the addition of P for adequate growth and yield. High productivity and a good competitive balance between the two crops were reached with only 22 kg ha⁻¹ of P, showing the great potential of cassava/cowpea intercropping on acid, infertile soils in the tropics.     

Evaluation of yield–density relationships and optimization of intercrop compositions of field-grown pea–oat intercrops using the replacement series and the response surface design

In a 2-year field experiment (2002/2003) on a loess soil near Göttingen/Germany, pea (Pisum sativum L.) and oat (Avena sativa L.) were grown alone and intercropped at a range of densities. Shoot biomass, grain yields and amount of N in grain were evaluated and optimized using two different replacement series and a hyperbolic yield–density equation describing a response surface to address the following questions: (i) what is the optimal composition of the pea–oat intercrop with regard to maximum yields, (ii) which intercropping design is most suitable to describe competition effects in pea–oat intercrops and the optimal intercrop compositions and (iii) which intercropping design is best suited for the evaluation of field data. For (i), the optimal intercrop compositions varied depending on the growth conditions for the crops. Furthermore, optimal intercrop compositions were found above the recommended sole crop densities. The density of oat had to be reduced more than that of pea, especially when optimal grain-N yields were desired and soil-N content was high. For maximum grain-N yields, pea could be sown at high densities in combination with 5–50% of the recommended density of oat. Thus, density can be used as a yield regulator for specific purposes such as a high N yield. The effects of competition at final harvest were described equally by both designs (ii). Oat was the clearly stronger and pea the inferior competitor. In contrast to the replacement series design, the hyperbolic yield–density equation was capable of adding valuable information about the extent of intra and interspecific competition. As intraspecific competition was consistently more important than interspecific competition, resource complementarity could be hold responsible for intercrop advantages. The highest intercrop advantage was found when total intraspecific competition was low, as shown by the relative yield total (RYT) and niche differentiation index (NDI) values >1. However, due to the RYT dependence on sole crops and total densities, the replacement series design led to misleading interpretations of the yield advantages. Both experimental designs were able to describe the field-data reliably (iii), but the response surface design had the advantage of being unaffected by insufficient field emergences, as it is not based on total densities. Numbers of plants m⁻² instead of seeds m⁻² can be used for the evaluation. Data from sole crops are not needed for the response surface design and thus the feared high experimental effort of this design can be reduced. However, when using the replacement series design, experimental effort should be greater than normal, as different sole crop densities and more intercrop compositions within a replacement series can lead to a more precise interpretation of the competition effects.     

Width of clover strips and wheat rows influence grain yield in winter wheat/white clover intercropping

Cereal–legume intercropping offers potential benefits in low-input cropping systems, where nutrient inputs, in particular nitrogen (N), are limited. In the present study, winter wheat (Triticum aestivum L.) and white clover (Trifolium repens L.) were intercropped by sowing the wheat into rototilled strips in an established stand of white clover.A field experiment was performed in two fields starting in two different years to explore the effects of width of the wheat rows and clover strips on the competition between the species and on wheat yields. The factors were intercropping (clover sole crop, wheat sole crop and wheat/clover intercropping), rototilled band width, sowing width and wheat density in a factorial experimental design that enabled some of the interactions between the factors to be estimated. The measurements included grain yield, ear density, grain weight, grain N concentration, dry matter and N in above-ground biomass of wheat, clover and weeds and profiles of photosynthetic active radiation (PAR) within the crop canopy.Intercropping of winter wheat and clover resulted in wheat grain yield decreases of 10–25% compared with a wheat sole crop. The yield reductions were likely caused by interspecific competition for light and N during vegetative growth, and for soil water during grain filling. N uptake in the wheat intercrop increased during late season growth, resulting in only small differences in total N uptake between wheat intercrops and sole crops, but increased grain N concentrations in the intercrop. Interspecific competition during vegetative wheat growth was reduced by increasing width of the rototilled strips from 7 to 14 cm, resulting in higher grain yields and increased grain N uptake. Increasing the sowing width of the wheat crop from 3 to 6 cm increased interspecific interactions and reduced wheat intraspecific competition during the entire growing season, leading to improved grain yields and higher grain N uptake.     

Comparative analysis of maize–soybean strip intercropping systems: a review

ABSTRACT

Traditional maize (Zea mays L.) and soybean (Glycine max (L) Merrill) intercropping practice cannot be adapted to modern agriculture due to low light use efficiency, radiation use efficiency, low comparative profits of soybeans and incompatibility with mechanization. However, a new type of maize and soybean intercropping system (MSIS) with high land equivalent ratio (LER) provides substantial benefits for small-land hold farmers worldwide. Our research team has done a wide range of research to suggest the appropriate planting geometry that ensures high yield and LER as high as 2.36, nutrient acquisition and mechanical operations in MSISs. Increase in the distance between soybean and maize rows and decrease in the spacing of maize narrow rows is useful for the high light interception for the short soybean in MSISs. This review concludes that MSIS has multifold and convincing results of LER and compatible with mechanization, while those practiced other than China still require technological advancements, agronomic measures and compatible mechanization to further explore its adaptability.