Interspecific competition,N use and interference with weeds in pea–barley intercropping

Field pea (Pisum sativum L.) and spring barley (Hordeum vulgare L.) were intercropped and sole cropped to compare the effects of crop diversity on productivity and use of N sources on a soil with a high weed pressure. ¹⁵N enrichment techniques were used to determine the pea–barley–weed-N dynamics. The pea–barley intercrop yielded 4.6 t grain ha⁻¹, which was significantly greater than the yields of pea and barley in sole cropping. Calculation of land equivalent ratios showed that plant growth factors were used from 25 to 38% more efficiently by the intercrop than by the sole crops. Barley sole crops accumulated 65 kg soil N ha⁻¹ in aboveground plant parts, which was similar to 73 kg soil N ha⁻¹ in the pea–barley intercrop and significantly greater than 15 kg soil N ha⁻¹ in the pea sole crop. The weeds accumulated 57 kg soil N ha⁻¹ in aboveground plant parts during the growing season in the pea sole crops. Intercropped barley accumulated 71 kg N ha⁻¹. Pea relied on N₂ fixation with 90–95% of aboveground N accumulation derived from N₂ fixation independent of cropping system. Pea grown in intercrop with barley instead of sole crop had greater competitive ability towards weeds and soil inorganic N was consequently used for barley grain production instead of weed biomass. There was no indication of a greater inorganic N content after pea compared to barley or pea–barley. However, 46 days after emergence there was about 30 kg N ha⁻¹ inorganic N more under the pea sole crop than under the other two crops. Such greater inorganic N levels during early growth phases was assumed to induce aggressive weed populations and interspecific competition. Pea–barley intercropping seems to be a promising practice of protein production in cropping systems with high weed pressures and low levels of available N.     

Pea–barley intercropping for efficient symbiotic N2-fixation,soil N acquisition and use of other nutrients in European organic cropping systems

Complementarity in acquisition of nitrogen (N) from soil and N₂-fixation within pea and barley intercrops was studied in organic field experiments across Western Europe (Denmark, United Kingdom, France, Germany and Italy). Spring pea and barley were sown either as sole crops, at the recommended plant density (P100 and B100, respectively) or in replacement (P50B50) or additive (P100B50) intercropping designs, in each of three cropping seasons (2003–2005). Irrespective of site and intercrop design, Land Equivalent Ratios (LER) between 1.4 at flowering and 1.3 at maturity showed that total N recovery was greater in the pea–barley intercrops than in the sole crops suggesting a high degree of complementarity over a wide range of growing conditions. Complementarity was partly attributed to greater soil mineral N acquisition by barley, forcing pea to rely more on N₂-fixation. At all sites the proportion of total aboveground pea N that was derived from N₂-fixation was greater when intercropped with barley than when grown as a sole crop. No consistent differences were found between the two intercropping designs. Simultaneously, the accumulation of phosphorous (P), potassium (K) and sulphur (S) in Danish and German experiments was 20% higher in the intercrop (P50B50) than in the respective sole crops, possibly influencing general crop yields and thereby competitive ability for other resources. Comparing all sites and seasons, the benefits of organic pea–barley intercropping for N acquisition were highly resilient. It is concluded that pea–barley intercropping is a relevant cropping strategy to adopt when trying to optimize N₂-fixation inputs to the cropping system.     

Growth,competition, yield advantage and economics in soybean/pigeonpea intercropping system in semi-arid tropics of India: I. Effect of subsoiling

Opinions differ on the necessity of deep tillage for sustaining crop productivity in the rainfed Vertisols of the semi-arid tropics of central India. We conducted a field experiment for 3 years (2000–2002) with a factorial combination of three cropping systems (sole soybean, sole pigeonpea and soybean/pigeonpea intercropping in 2:1 row ratio) and three tillage practices (conventional, conventional + subsoiling in alternate years and conventional + subsoiling every year). Objectives were (i) to examine the effect of subsoiling Vertisols on sustaining yield of soybean/pigeon pea intercropping, and (ii) to assess the frequency of subsoiling for realizing maximum yield and profit. Though there was a reduction in growth and yield of intercrops, higher soybean equivalent yield (SEY) and area-time equivalent ratio (ATER) value in soybean/pigeonpea intercropping system as compared to sole soybean had a yield advantage. The average yield advantage in intercropping system was 60% higher than that from sole soybean. The yield advantage of intercropping system in terms of ATER was 7% greater with subsoiling than conventional tillage. The yield response to subsoiling was consistent over the period and on an average, subsoiling increased yield by 20%. The effect was associated with improved water storage and root length density. However, with respect to energy use efficiency and profit, the effect of subsoiling was comparable to conventional tillage. The variation in net return and benefit:cost ratio in subsoiling every year and subsoiling in alternate years in sole soybean and soybean/pigeonpea intercropping was not significant. However, in sole pigeon pea subsoiling every year out-yielded subsoiling in alternate years. The interactive effect of subsoiling and intercropping increased the yield by 21–25%. Thus, under rainfed cropping where drought of unpredictable intensity and duration is a prevailing feature, soybean/pigeon pea intercropping could be a promising option, especially when combined with subsoiling in alternate years.     

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.     

Density and relative frequency effects on competitive interactions and resource use in pea–barley intercrops

Intercropping advantages may be influenced by both plant density and relative frequency of the intercrop components. In a field study barley (Hordeum vulgare L.) and pea (Pisum sativum L.) were sole cropped and intercropped at three densities and with two relative frequencies when intercropped.Earlier seedling emergence gave barley an initial growth advantage, assessed using the relative efficiency index (REIc), whereas pea was in general more growth efficient once the initial growth phase had been passed. This reversal in relative growth efficiency along with the observation that early barley dominance did not appear to suppress pea growth indicates that differences in phenology played a role in shaping the prevailing dynamics. Whereas increases in plant density had a positive effect on the growth of pea, the growth of intercropped barley was severely limited by increases in density at the end of the growing period and more so in the pea dominated intercrop. At the final harvest land equivalent ratios (LER) of 0.9–1.2 express resource complementarity in almost all studied intercrops, complementarity that was not directly affected by changes in plant density or relative frequency.Intercropped pea did not increase its reliance on atmospheric nitrogen fixation compared to the pea sole crop. With respect to soil nitrogen uptake there were no effect of plant density but a strong effect of the relative frequency of pea in the intercrop, the greater the proportion the lower the uptake.Changes in the competitive strength of the pea and barley crop over the growing season had a marked effect on the proportion of pea in the final grain yields of the intercrops. At low and recommended density the proportions of pea and barley in the final grain yield was not markedly different from the expected proportions sown; however, at high density the suppression of barley strongly increased the proportion of pea in the final grain yield.Weed infestation levels decreased as density was raised and the suppressing effect of density was clearly stronger the greater the frequency of pea in the crop. Earlier germination and tillering ability of barley are seen as likely explanations of lower weed load in the barley dominated crop treatments.This study points at the potential of employing density and relative crop frequency as “regulators” when specific intercrop objectives such as increased competitiveness towards weeds or specific grain yield composition are wanted.     

The competitive ability of pea-barley intercrops against weeds and the interactions with crop productivity and soil N availability

Grain legumes, such as peas (Pisum sativum L.), are known to be weak competitors against weeds when grown as the sole crop. In this study, the weed-suppression effect of pea-barley (Hordeum vulgare L.) intercropping compared to the respective sole crops was examined in organic field experiments across Western Europe (i.e., Denmark, the United Kingdom, France, Germany and Italy). Spring pea (P) and barley (B) were sown either as the sole crop, at the recommended plant density (P100 and B100, respectively), or in replacement (P50B50) or additive (P100B50) intercropping designs for three seasons (2003-2005). The weed biomass was three times higher under the pea sole crops than under both the intercrops and barley sole crops at maturity. The inclusion of joint experiments in several countries and various growing conditions showed that intercrops maintain a highly asymmetric competition over weeds, regardless of the particular weed infestation (species and productivity), the crop biomass or the soil nitrogen availability. The intercropping weed suppression was highly resilient, whereas the weed suppression in pea sole crops was lower and more variable. The pea-barley intercrops exhibited high levels of weed suppression, even with a low percentage of barley in the total biomass. Despite a reduced leaf area in the case of a low soil N availability, the barley sole crops and intercrops displayed high weed suppression, probably because of their strong competitive capability to absorb soil N. Higher soil N availabilities entailed increased leaf areas and competitive ability for light, which contributed to the overall competitive ability against weeds for all of the treatments. The contribution of the weeds in the total dry matter and soil N acquisition was higher in the pea sole crop than in the other treatments, in spite of the higher leaf areas in the pea crops.     

Agronomic,forage quality and economic advantages of red pea (Lathyrus cicera L.) intercropping with wheat and oat under low‐input farming

Red pea–cereal intercropping could provide animal feed with agronomic and economic advantages. The growth rate, forage yield, quality, interspecific competition and financial outcome of intercrops of red pea (Lathyrus cicera L.) with wheat (Triticum aestivum L.) and oat (Avena sativa L.) in two different seeding ratios (60:40, 80:20) were estimated. Growth rate of species was lower in the intercrops than in monocrops, especially in red pea–oat intercrops due to the strong competitive ability of oat. Red pea–oat intercrop of 60:40 produced the highest biomass (10.83 Mg/ha) and crude protein yield (1,116 kg/ha). Land equivalent ratio (LER) values were greater for the red pea with wheat (1.13) and oat 60:40 (1.09) indicating an advantage of intercropping in terms of dry‐matter (DM) yield, while red pea:oat 60:40 ranked first for LER for nitrogen yield. Aggressivity and partial actual yield loss indicated cereals as the dominant species. The highest monetary advantage index was recorded for the red pea:wheat 60:40 and the highest intercropping advantage value was recorded for the red pea:oat 80:20. In conclusion, most intercrops of red pea with wheat and oat showed significant advantages relative to their monocrops due to better DM production, resource‐use efficiency and economics under low‐input farming.     

Growth,competition, yields advantage and economics in soybean/pigeonpea intercropping system in semi-arid tropics of India: II. Effect of nutrient management

Low native nitrogen (N) and phosphorus (P) coupled with imbalanced nutrient application is a major constraint limiting productivity of intercropping systems on Vertisols of the semi-arid tropical India. In a 3-year field experiment competition behaviour of component crops for nutrients use in soybean/pigeonpea intercropping system was assessed based on relative yield (RY), relative nitrogen yield (RNY) and relative phosphorus yield (RPY) under three nutrient levels (0 NPK, 100% NPK (N:P:K = 30:26:25 kg ha⁻¹) and 100% NPK + 4 t FYM ha⁻¹). The result showed that before soybean harvest, the RY and RNY of soybean were greater (1.0) than the corresponding values of RY and RNY of pigeon pea (0.6). This implied that competition exists for soil N between the component crops during the first half of the cropping system. It was observed that soybean harvest did not coincide with peak flowering of pigeonpea, the stage when biological nitrogen fixation (BNF) was maximum. Thus, BNF dependency of pigeonpea was low before soybean harvest and the plants suffered from N deficiency more when no fertilizer-N was applied and diminished at a high-N level. Pigeon pea attained its peak flowering after the harvest of soybean and increased its dependency on BNF when soil N was exhausted by soybean. Thus, after the harvest of soybean, RY and RNY of pigeon pea gradually increased and approached 1.0 at maturity at all nutrient levels. The RPY values showed that phosphorus was not the limiting factor to any of the crop in the system even if it was not applied. The study thus suggests that in the soybean/pigeonpea intercropping system, N is a limiting factor for growth of pigeonpea intercrop during the first half of its growth and application of 100% NPK (30 kg N) + 4 t FYM could meet N demand of pigeonpea in N deficient soils as this nutrient management option gave higher yield, root length density and profit under soybean/pigeonpea intercropping system than 100% NPK and control.     

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.     

Adaptation of the STICS intercrop model to simulate crop growth and N accumulation in pea–barley intercrops

Cereal–legume intercrops are gaining increasing interest in Europe. Modelling, by taking into account the complexity of species interactions, can be a very useful tool to study such systems and to test new strategies in various soil and climatic conditions. The present work describes the adaptation of an intercrop model for pea–barley intercrops through the extrapolation of the STICS sole crop model and its parameterisation from experimental data recorded on sole crops. Several improvements have been added to the existing crop model to allow an inversion of dominance in height between species during the crop cycle and a trophic link between crop growth rate and the potential for N₂ fixation. A 2-year dataset on pea and barley sole crops grown under non-limiting water conditions and with full crop protection was first used for calibration. The intercrop model was subsequently tested on experimental datasets of pea–barley intercrops grown under the same conditions as the sole crops. The intercrop experiments used to test the intercrop model differed in soil type, soil N supply and plant densities of each species.     

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.     

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.     

Growth and distribution of maize roots under nitrogen fertilization in plinthite soil

To improve efficiency of soil N and water use in the savanna, maize (Zea mays L.) cultivars with improved root systems are required. Two rainfed field experiments were conducted in Samaru, Nigeria in the 1993 and 1994 growing seasons with five maize cultivars under various rates of nitrogen fertilizer. The capacity of maize for rapid early root growth and to later develop a deep, dense root system was assessed. In addition, the effect of N fertilization on root growth of maize was studied in 1994. The widely cultivated cultivar TZB-SR had a poor root system in the surface soil layer and was more susceptible to early-season drought, as indicated by low plant vigor and aboveground dry matter yield during that time. It had a lower grain yield and a relatively small harvest index, but ranked among the highest in total aboveground dry matter production compared to other cultivars. The size of root system alone did not always relate well with grain yield among cultivars. Partitioning of dry matter within the plant was important in determining differences in grain yield and N stress tolerance between cultivars. A semiprolific cultivar (SPL) had high seedling vigour and a dense root system in the surface soil layer that conferred a greater tolerance to early-season drought stress and improved uptake of the early-season N flush, as indicated by a greater dry matter yield at 35 days after sowing (DAS). It also had a fine, deep, dense root system at flowering that could have improved water- and N-use efficiency in the subsoil (> 45 cm), thereby avoiding midseason drought stress in 1994. SPL had a large harvest index and the greatest yield among cultivars in 1994. Averaged across cultivars, greater root growth and distribution was observed at a moderate N rate of 0.56 g plant⁻¹ than at zero-N or high N (2.26 g plant⁻¹). Differences in root morphology could be valuable as selection criteria for N-efficient and drought-tolerant maize.     

Yield response to plant density of maize and sunflower intercropped with soybean

Maize-soybean and sunflower-soybean intercrops have the potential for increasing yield per unit land area and time in fully mechanized farming systems. The objectives of this work were to measure the land equivalent ratio index of maize and sunflower intercropped to soybean, to assess the effects of plant density of its components, and to gain insight into ecophysiological processes affecting their yield determination. Maize-soybean and sunflower-soybean intercrops and their respective sole crops were grown at Balcarce, Argentina during two growing seasons. Treatments included a wide range of plant densities for sole and intercropped sunflower (2-9 plants m⁻²) and maize (4-12 plants m⁻²). Plants were harvested to determine shoot dry matter and grain yield per plot and at the individual plant level. Land equivalent ratio index (LER) increased 11% (mean of the two years) when plant density of sunflower was reduced from 6 to 3 plants m⁻²; and LER increased 5% (year 1) or it was maintained (year 2) when maize plant density was reduced from 8 to 4 plants m⁻². Yield response to plant density of sunflower and maize influenced LER. The response to plant density of intercropped sunflower and maize grain yield followed the same pattern than that in a sole crop, and grain yield of intercropped sunflower or maize were lower than those for the sole crops at each plant density except at the lowest sunflower plant density. Yield reductions from sole crop to intercrop at each plant density averaged 20% and were associated (i) with lower intra-row spacing in the intercrop and (ii) with a lower shoot production rather than to a change in the dry matter partitioning to reproductive structures; in addition, detrimental effects of soybean over maize or sunflower yield were undetectable.     

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.     

The effect of late-season urea spraying on grain yield and quality of winter wheat cultivars under low and high basal nitrogen fertilization

The late-season foliar application of urea may increase yield and grain quality of wheat (Triticum aestivum L.). Limited information is available regarding the effect of late urea spraying on the performance of wheat cultivars under various basal N fertilization rates. Field experiments were conducted during 2000 through 2002 to evaluate the responses of six winter wheat cultivars to foliar urea (30 kg N ha⁻¹) treatment around flowering at low (67 kg N ha⁻¹) and high (194 kg N ha⁻¹) basal N fertilization rates. Following urea spraying at low N rate, all cultivars increased grain yields to a similar extent (by an average of 7.8% or 509 kg ha⁻¹) primarily due to an increase in the 1000-kernel weight. No yield response to the late-season urea treatment occurred at high basal N rate where grain yields averaged 24.9% (1680 kg ha⁻¹) higher than those at low N rate. In contrast, late foliar urea application similarly improved grain quality at both low and high N rates by an average of 5 g kg⁻¹ (4.5%) for protein content, 3.2 cm³ (11.9%) for Zeleny sedimentation, and 20 g kg⁻¹ (8.6%) for wet gluten. These quality increments were consistent in all growing seasons regardless of significant variations in grain yields and protein concentrations across years. However, most cultivars failed to achieve breadmaking standards at low N rate as quality increments associated with the urea treatment were relatively small when compared to those achieved by high basal N rate. Late urea spraying had no effect on the falling number, whereas some cultivars showed small, but significant reduction in the gluten index at both N rates. Cultivars improved the hectolitre weight with the late-season urea treatment only at low N rate. Significant cultivar × urea interactions existed for most quality traits, which were due to the cultivar differences in the magnitude of responses. Thus, late-season urea spraying consistently produced larger yields at low basal N rate, and resulted in cultivar-dependent increases in protein content, Zeleny sedimentation, and wet gluten at both low and high N rates.     

Intraspecific responses in crop growth and yield of 20 soybean cultivars to enhanced ultraviolet-B radiation under field conditions

Field studies were conducted to determine the potential for intraspecific responses in crop growth and grain yield of 20 soybean cultivars to enhanced ultraviolet-B (UV-B, 280–315 nm) radiation. The supplemental UV-B radiation was 5.00 kJ m⁻², simulating a depletion of 20% stratospheric ozone at Kunming (25°N, 1950 m). Out of the 20 soybean cultivars tested, 17 and 15 showed significant change in plant height at 80 DAP (days after planting) and ripening stages, respectively. Sensitivity in plant height was greater at 80 DAP than at ripening. The plant height of 3 cultivars increased, and that of 17 cultivars decreased. Under UV-B radiation, LAI (leaf area index), biomass and grain yield decreased, respectively. The greatest percent decrease was 95.7, 93.9 and 92.8, respectively. RI (response index) was the sum of percent change in plant height at ripening, LAI, biomass and grain yield. The results showed that all 20 soybean cultivars had a negative RI, indicating inhibition by UV-B radiation on soybean growth. The RI of 6 tolerant cultivars was higher than −163.1 and 5 out of 6 originated from south China (low latitude). The RI of the most tolerant cultivars, Yunnan 97801, was −72.4. Meanwhile, the RI of 5 sensitive cultivars was lower than −256.9 and 4 out of the 5 originated from north China (high latitude). The RI of the most sensitive cultivar, Huanxianhuangdou, was −295.7. These UV-B tolerant cultivars identified in this study might be useful in breeding programs.     

The combined effects of nitrogen fertilizer and density of the legume component on production efficiency in a maize/cowpea intercrop system

The combined effects of applied nitrogen and of legume density on the yields and efficiency of cereal/legume intercropping were examined, using maize and cowpea. The levels of applied nitrogen were 0, 30, 60 and 120 kg N ha⁻¹, and intercrop cowpea densities were 80 000, 100 000, 120 000 and 150 000 plants ha⁻¹. The interaction of applied N and density of companion cowpea on yield of maize was negative. In maize, the yield losses due to intercropping were alleviated to some degree by N application, but in cowpea they were accentuated, and it appeared that maize was more competitive than cowpea. Maize was more efficient than cowpea in the utilization of N to produce grain; with each increment of N, efficiency declined in maize but was almost constant in cowpea. The Land Equivalent Ratio (LER), a measure of the efficiency of intercropping, declined with increasing levels of applied N but did not change significantly when intercrop cowpea density exceeded 100 000 plants ha⁻¹. The LER values followed trends in cowpea rather than maize yields, and this may be attributed to shading of cowpea by maize.     

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.