Effects of Cropping System, Seed Bed Management and Fertility Interactions on Biomass of Crops Grown on a Vertisol in the Central Highlands of Ethiopia

In the Ethiopian highlands, where integrated crop and livestock production takes place, the inadequate supply, in both quantity and quality, of feeds during the year is a major constraint. Native pastures and crop residues are the major feed sources, but their quality is often poor. Integration of forage legumes in the cropping system is one alternative to improve the fodder quality. Results of field work conducted over two seasons in order to assess and evaluate the potential yields of crops, crop/forage combinations and rotation systems on a Vertisol under two seed bed preparation systems showed that intercropping wheat with clover or sequential cropping of an oat/vetch mixture followed by chickpea provided high-quality fodder; the effect was greater under fertilized conditions. In addition, where monocropping treatment was tested, legume–cereal rotation resulted in higher grain and fodder yield when compared to cereal–cereal rotation. The study also showed that two short-duration crops could be produced in sequence per year. It is therefore suggested that the Vertisols in the Ethiopian highlands could provide a good opportunity for longer period cropping using improved food and forage crops, thereby improving the availability and quality of animal feed and protecting the land against erosion.     

Crop Rotation to Improve Agricultural Production in Sub-Saharan Africa

A three years' trial was conducted in a farmers' field in northern Ghana to evaluate the effect of sole crops (cotton, cowpea, groundnut, soybean, and sunflower) planted once or twice on yield of the staple foods of the region, maize and sorghum. Sole cropping for only one year already resulted in significant yield increases for maize and partly for sorghum compared to the conventional cropping of mixed stands of maize–sorghum or maize–groundnut and natural fallow. Lowest yield of maize and sorghum was obtained where these cereals followed maize–sorghum (monoculture). Intercropping of maize with groundnut led to subsequent maize and sorghum yields which were similar to those obtained after maize–sorghum. After growing legumes and sunflower for one year the grain and straw yield of maize and sorghum was significantly higher in the two consecutive years than after cereal (maize–sorghum) monoculture. In this trial maize and sorghum were found to be not as tolerant to the disadvantages of monoculture or preceding cereals–legumes mixture. The results suggest that continuous intercropping with cereals under the given conditions has negative effects on soil fertility and can lead to an increase in soil-borne pests and troublesome weeds like Striga comparable to monocropped cereals.     

The Effects of Sowing Date on the Growth and Nutritive Value of Lablab purpureus

In two similar experiments, Lablab purpureus was sown at different dates in July and August to evaluate the effects of sowing date on the yield and nutritive value of the plant and shed leaves. On each occasion, an interim harvest was performed on half of the plants sown at each date and the regrowth recorded. The interim harvest reduced the total yield, and in particular that of shed leaves. In one of the two experiments, late sowing resulted in a considerable reduction in yield, increased crude protein and reduced modified acid-detergent fibre concentrations. Ash concentrations were higher in plants sown later and their shed leaves. Sodium concentrations were inadequate for ruminants and, like phosphorus concentrations, tended to decrease with later sowing. However, both calcium and magnesium concentrations increased with later sowing and were sufficient for ruminant production. Potassium concentrations were high and were little affected by sowing date. It is concluded that both an interim harvest and late sowing are disadvantageous when lablab is grown for ruminant livestock, the former because of yield reduction and the latter because of yield reduction, increases in ash concentration and reductions in sodium and phosphorus concentrations.     

Growth and Yields of Intercropped Sorghum and Sunflower (Helianthus annuus L.) in Semi-arid Nigeria

Effect of five planting patterns on the growth, yield and yield components of intercropped sunflower and sorghum was studied during 1989–90 planting seasons at University of Maiduguri, Nigeria. Generally, intercropping depressed the performance of sorghum more than sunflower. Sorghum plants grown in alternate hills with sunflower had the shortest stems, the least dry matter and total seed yields per hectare, while the highest dry matter and seed yields were obtained from sorghum planted in five alternating rows with sunflower. Similarly, in sunflower, plants grown in five alternating rows with sorghum had the highest yields compared with other planting patterns, but there were no significant differences in the dry matter and total seed yields of sorghum and sunflower intercropped in three and five alternating rows. Light transmission, leaf area index and yields of both crops followed similar trends under the various planting patterns. Interplanting in five alternating rows that allowed the highest leaf area also allowed the lowest light transmission and produced the highest yields. Land use efficiency was highly improved under three and five rows interplanting by 52 and 74 % respectively.     

Sorghum grain yield,forage biomass production and revenue as affected by intercropping time

Sorghum is an excellent alternative to other grains in poor soil where corn does not develop very well, as well as in regions with warm and dry winters. Intercropping sorghum [Sorghum bicolor (L.) Moench] with forage crops, such as palisade grass [Brachiaria brizantha (Hochst. ex A. Rich) Stapf] or guinea grass (Panicum maximum Jacq.), provides large amounts of biomass for use as straw in no-tillage systems or as pasture. However, it is important to determine the appropriate time at which these forage crops have to be sown into sorghum systems to avoid reductions in both sorghum and forage production and to maximize the revenue of the cropping system. This study, conducted for three growing seasons at Botucatu in the State of São Paulo in Brazil, evaluated how nutrient concentration, yield components, sorghum grain yield, revenue, and forage crop dry matter production were affected by the timing of forage intercropping. The experimental design was a randomized complete block design. Intercropping systems were not found to cause reductions in the nutrient concentration in sorghum plants. The number of panicles per unit area of sorghum alone (133,600), intercropped sorghum and palisade grass (133,300) and intercropped sorghum and guinea grass (134,300) corresponded to sorghum grain yields of 5439, 5436 and 5566 kg ha⁻¹, respectively. However, the number of panicles per unit area of intercropped sorghum and palisade grass (144,700) and intercropped sorghum and guinea grass (145,000) with topdressing of fertilizers for the sorghum resulted in the highest sorghum grain yields (6238 and 6127 kg ha⁻¹ for intercropping with palisade grass and guinea grass, respectively). Forage production (8112, 10,972 and 13,193 Mg ha⁻¹ for the first, second and third cuts, respectively) was highest when sorghum and guinea grass were intercropped. The timing of intercropping is an important factor in sorghum grain yield and forage production. Palisade grass or guinea grass must be intercropped with sorghum with topdressing fertilization to achieve the highest sorghum grain yield, but this significantly reduces the forage production. Intercropping sorghum with guinea grass sown simultaneously yielded the highest revenue per ha (€ 1074.4), which was 2.4 times greater than the revenue achieved by sowing sorghum only.     

Yield and Yield Components from Intercropping Improved Bush Bean Cultivars with Maize

Bush bean ( Phaseolus vulgaris L.) is widely intercropped with maize ( Zea mays L.) in North-west Spain. Little information is available on the relative performance of elite bush bean cultivars when intercropped or on the effect of bush bean on performance of the maize crop. This two-environment study presents the interactions between improved bush bean cultivars and maize on yield and yield components. Eight treatments (four bean/maize intercrops and four sole crops, two of bean and two of maize) were tested using a randomized complete block design with four replications in two environments. Bean and maize were planted simultaneously in alternate rows when intercropped. Significant treatment differences were observed for bean and maize moisture, pod and cob percentage, bean and maize yield, ears per plant and ear length. Location effects were significant for bean and maize moisture and pod percentage. Significant treatment by location interactions occurred for pod percentage and ear length. Intercropping reduced yield by between 40 and 60 % for bush bean cultivars, and by 45 % for both maize cultivars. Mean yields were used to calculate the land equivalent ratio (LER), which averaged 1.01 in Pontevedra but 0.93 in La Coruña. Intercropping of bush bean with maize did not make better use of land than conventional sole cropping under these environmental conditions. It is suggested that this was probably due to the amount and distribution of rain in relation to crop growth. Approaches that might be expected to result in improved land usage are presented.     

Uniformity, Performance and Seed Quality of Soybean (Glycine max (L.) Merrill) Seed Crops Grown from Sub-samples of One Seed Lot Obtained after Selection for Physical Seed Attributes

In a glasshouse experiment it was examined whether narrow grading and selection from a commercial soybean seed lot cultivar 'IAS-5', could improve the uniformity of the seed crop grown from it and thereby enhance yield, quality and uniformity of seeds produced. The classes created were: Control (original seed lot); Size-graded seeds (projected area measured by image analysis 37–46 mm²); Non-cracked seeds; Yellow seeds; Size-graded sound seeds (size-graded, non-cracked, yellow, non-wrinkled, non-etched). Compared to the control, percentage of emergence, survival and number of yielding plants were enhanced in crops from non-cracked, yellow or size-graded sound seeds. Differences in plant numbers did not result in differences in crop yield. The different seed lots also did not differ in crop uniformity: time interval between stages of plant development, plant height 20 days after sowing, yield components, physical or physiological quality attributes of seeds produced, and respective coefficients of variation were similar. Fewer plants survived in crops showing a larger variation in plant height 20 days after sowing, thus reducing differences in initial plant-to-plant variation. Creating more uniform crops by additional grading or selection of commercial seed lots may therefore not be promising.     

Phenological and physiological evaluation of first and second cropping periods of sorghum and maize crops

Environmental conditions influence phenology and physiological processes of plants. It is common for maize and sorghum to be sown at two different periods: the first cropping (spring/summer) and the second cropping (autumn/winter). The phenological cycle of these crops varies greatly according to the planting season, and it is necessary to characterize the growth and development to facilitate the selection of the species best adapted to the environment. The aim of this study was to characterize phenological phases and physiological parameters in sorghum and maize plants as a function of environmental conditions from the first cropping and second cropping periods. Two parallel experiments were conducted with both crops. The phenological characterization was based on growth analyses (plant height, leaf area and photoassimilate partitioning) and gas exchange evaluations (net assimilation rate, stomatal conductance, transpiration and water-use efficiency). It was found that the vegetative stage (VS) for sorghum and maize plants was 7 and 21 days, respectively, longer when cultivated during the second cropping. In the first cropping, the plants were taller than in the second cropping, regardless of the crop. The stomatal conductance of sorghum plants fluctuated in the second cropping during the development period, while maize plants showed decreasing linear behaviour. Water-use efficiency in sorghum plants was higher during the second cropping compared with the first cropping. In maize plants, in the second cropping, the water-use efficiency showed a slight variation in relation to the first cropping. It was concluded that the environmental conditions as degree-days, temperature, photoperiod and pluvial precipitation influence the phenology and physiology of both crops during the first and the second cropping periods, specifically cycle duration, plant height, leaf area, net assimilation rate, stomatal conductance and water-use efficiency, indicating that both crops respond differentially to environmental changes during the growing season.     

Agronomic Performance of Sorghum and Groundnut Cultivars in Sole and Intercrop Cultivation under Semiarid Conditions

The performance of sorghum and groundnut cultivars was studied in sole cropping and intercropping systems at Babile in the semiarid area of eastern Ethiopia in 1996, 1997 and 1999. On average, late-maturing cultivars of groundnut and sorghum gave higher dry pod yield and grain yield, respectively, when intercropped with early-maturing cultivars of the associated crops. The significant variation among groundnut cultivars in yield and yield components under intercropping with sorghum cultivars revealed that sole cropping may not provide the appropriate environment for selecting varieties intended for use in intercropping. The productivity of intercropped groundnut and sorghum cultivars, as determined by total land equivalent ratios (LER), was higher than sole cropping, indicating the presence of temporal complementarity in the use of growth resources. A mean yield advantage of 32 % was obtained under intercropping.     

Evolution in crop–livestock integration systems that improve farm productivity and environmental performance in Australia

Australian farming systems have an enduring history of crop–livestock integration which emerged in the face of high climate variability, infertile soils and variable landscapes. Ley farming systems with phases of shorter annual legume pasture phases with cereal crops predominate but, emerging sustainability issues and the need to manage risk is driving ongoing innovation in crop–livestock integration. We discuss the recent evolution of selected innovations that integrate crop and livestock production and their impacts on farm productivity, sustainability and business risk. Dual-purpose use of cereals and canola (Brassica napus) for forage during the vegetative stage while still harvesting for grain is now practiced throughout southern Australia's cropping zone. This practice provides risk management benefits, diversifies crop rotations, reduces pressure on other feed resources and can significantly increase both livestock and crop productivity from farms by 25–75% with little increase in inputs. Sacrificially grazing crops when expected grain yield is low and/or livestock prices are attractive relative to grain provides further flexibility in crop–livestock management systems vital for business risk management in a variable climate. Replacing annual pastures with perennial pasture phases in rotation with crops can provide a range of benefits including improved hydrological balance to reduce dryland salinity, subsoil acidification and water-logging, provide a management tool for herbicide-resistant or problem weeds, improved soil nutrient and carbon stocks as well as increased livestock productivity by filling feed gaps. In some environments, integration of perennial forages in mixtures with cropping, such as alley cropping and inter-cropping, also provide options for improving environmental outcomes. These practices are all innovations that provide flexibility and enable tactical decisions about the mix of enterprises and allocation of land and forage resources to be adjusted in response to climate and price. We discuss these innovations in the context of the emerging constraints to crop–livestock integration in Australia including the continuing decline in labour availability on farms and increasing management skill required to optimise enterprise profitability.     

Relay-intercropped forage legumes help to control weeds in organic grain production

In organic grain production, weeds are one of the major limiting factors along with crop nitrogen deficiency. Relay intercropping of forage legume cover crops in an established winter cereal crop might be a viable option but is still not well documented, especially under organic conditions.Four species of forage legumes (Medicago lupulina, Medicago sativa, Trifolium pratense and Trifolium repens) were undersown in six organic wheat fields. The density and aerial dry matter of wheat, relay-intercropped legumes and weeds were monitored during wheat-legume relay intercropping and after wheat harvest until late autumn, before the ploughing of cover crops.Our results showed a large diversity of aerial growth of weeds depending on soil, climate and wheat development. The dynamics of the legume cover crops were highly different between species and cropping periods (during relay intercropping and after wheat harvest). For instance, T. repens was two times less developed than the other species during relay intercropping while obtaining the highest aerial dry matter in late autumn. During the relay intercropping period, forage legume cover crops were only efficient in controlling weed density in comparison with wheat sole crop. The control of the aerial dry matter of weeds at the end of the relay intercropping period was better explained considering both legumes and wheat biomasses instead of legumes alone. In late autumn, 24 weeks after wheat harvest, weed biomass was largely reduced by the cover crops. Weed density and biomass reductions were correlated with cover crop biomass at wheat harvest and in late autumn. The presence of a cover crop also exhibited another positive effect by decreasing the density of spring-germinating annual weeds during the relay intercropping period.     

Relay Cropping of Sorghum and Legume Shrubs for Crop Yield Improvement and Striga Control in the Subsistence Agriculture Region of Tigray (Northern Ethiopia)

Striga hermonthica is a major constraint in the subsistence agriculture regions of northern Ethiopia. Low soil fertility and overall environmental degradation has contributed to the build up of the parasitic weed infestation. Improved cropping systems have to be introduced to address the interrelated problems of Striga and soil fertility decline. Thus, relay cropping of sorghum with legume shrubs was investigated at two locations representing different environments. Results showed that the output of the improved cropping system was dependent on ecological endowments. Relay cropping led to significant improvement in yield at Sheraro, at the site with relatively better weather and soil conditions. The legume shrubs resulted in significantly lower sorghum yield in a dryland location (Adibakel). Overall Striga infestation declined over the 3‐year period; however, treatment differences were not apparent. Among the two legume shrubs, Sesbania sesban was better adapted to the dryland areas. Relay cropping could provide a viable option for farmers in both types of environments that are characterized by accelerated decline in natural resource base. However, it could mean compromising the yield of non‐fertilized sorghum in the interest of long‐term benefits of low incidence of Striga and more rewarding crop enterprise in dry areas.     

Effect of spring fertilization on ecosystem services of organic wheat and clover relay intercrops

Nitrogen (N) deficiency and weed infestation are main factors limiting yield and yield stability in organic wheat. Organic fertilizers may be used to improve crop performance but off-farm input costs tend to limit profitability. Instead, forage legumes may be inserted into the crop rotation to improve the N balance and to control weed infestation. In opposition to simultaneous cropping, relay intercropping of legumes in organic winter wheat limits resource competition for the legume cover crop, without decreasing the performance of the associated wheat.The aim of this study is to evaluate the effect of spring organic fertilization on the performance of intercropped legumes and wheat, and on services provided by the legume cover.Two species of forage legumes (Trifolium pratense L. and Trifolium repens L.) were undersown in winter wheat (Triticum aestivum L. cv Lona) in five organic fields during two consecutive crop seasons. Organic fertilizer was composed of feather meal and applied on wheat at legume sowing. The cover crop was maintained after the wheat harvest and destroyed just before sowing maize.Spring organic nitrogen fertilization increased wheat biomass (+35%), nitrogen (+49%), grain yield (+40%) and protein content (+7%) whatever the intercropping treatment. At wheat harvest, red clover biomass was significantly higher than white clover one (1.4 vs. 0.7 t ha⁻¹). Nitrogen fertilization decreased forage legume above-ground biomass at wheat harvest, at approximately 0.5 t ha⁻¹ whatever the specie. No significant difference in forage legume biomass production was observed at cover killing. Nitrogen accumulation in legume above-ground tissues was significantly higher for white clover than for red clover. Both red and white clover species significantly decreased weed infestation at this date. Nitrogen fertilization significantly increased weed biomass whatever the intercropping treatment and decreased nitrogen accumulation in both clover species (−12%).We demonstrated that nitrogen fertilization increased yield of wheat intercropped with forage legume while the performance of legumes was decreased. Legume growth was modified by spring fertilization whatever the species.     

Grain Yield of Intercropped Sorghum and Pearl Millet as Influenced by Sorghum Genotype and Cropping Pattern

Intercropping of sorghum and pearl millet with different growth cycles is used widely in third-world countries to ensure and increase yields. However, it is questionable whether yield increases because of intercropping can be maintained under more developed systems, since temporal differences are necessary to allow mechanized planting and harvesting.
Three sorghum hybrids with expected growth cycles from 90 to 110 days were planted in sole stands and in alternate rows and mixed within the rows with a pearl millet hybrid having a growth cycle similar to that of the early sorghum. Sole stands of millet also were included. The plots were planted at three locations in Kansas, two dryland and one including dryland and irrigated. Results show that yields were consistently highest in sole stands of sorghum, owing to the higher yield level of sorghum. No yield increase could be found on a land equivalent ratio basis, indicating no intercropping advantages. However, under good moisture conditions, a tendency toward yield increase was observed with the later maturing sorghums, which had 1–2 weeks of grain filling after the millet was mature. When moisture supply was insufficient, millet showed higher competitiveness for water than sorghum, and sorghum was adversely affected more than pearl millet was favored. It was concluded that moisture conditions have to be good and that temporal differences between sorghum and millet have to be greater than those used in this experiment to achieve intercropping yield advantages.     

Irrigation Water Management for Efficient Water Use in Mulched Onion

Caused by the necessarily imperfect seed placement accuracy of sowing machines and, additionally, caused by many other biotic and abiotic factors, the resulting plant stands exhibit nonregular spatial distributions of its plants. Based on several simplifying assumptions, a stochastic approach is developed which allows an estimation of the effects of nonregular spatial patterns on yield per area. In this approach, two random variables are attached to each plant: single plant yield E and individual space A . The latter is estimated by the area of Thiessen polygons. Yield per area, calculated by the expectation of the ratio E/A , can be approximately expressed dependent on the means ( Ē and Ā ) and coefficients of variation ( v _E and v _A ) of E and A and their correlation ( r _EA ). In relation to the commonly used estimate Ē/Ā for yield per area, one obtains yield decreases if v _A / v _E  <  r _EA . This inequality, however, will be usually valid in the field of applications. The theoretical approaches and results were applied to three experimental data sets for drilled seeds of winter oilseed rape ( Brassica napus L.) (plant density: 60 plants m⁻², row distance: 10 cm). These data sets are characterized by different accuracies of longitudinal distributions within rows (58 %, 101 %, 150 %): yield depression increases with an increasing variability of plant distances within rows.     

Reduced inter-row distance improves yield and competition against weeds in a semi-dwarf durum wheat variety

Weed and nutrient management in cropping systems of semi-arid areas is a major constraint to cereal yield. Where the use of herbicides is banned or discouraged, the competitive ability of a crop is crucial to reduce weed growth and diffusion. Genotypic differences in the competitive abilities of crops are an important trait to reduce weeds, especially for plant height. However, there is contrasting information about the interactions of other management practices and genotypic traits on wheat yield and competitive ability against weeds and weed growth. The present study investigated yield and quality of durum wheat (Triticum durum Desf.) and weed growth and composition for two wheat cultivars with contrasting competitive abilities against weeds. Wheat was grown under three spatial arrangements (5-cm, 15-cm, 25-cm inter-row distance) and three sowing densities, and broadleaf weeds were either removed or not. The sowing rate did not affect the yield of these wheat cultivars or the weed growth. Reduced inter-row distance dramatically reduced weed biomass for both wheat cultivars, and increased wheat yield and nitrogen uptake in the low-competitive, high-yielding, semi-dwarf cv. ‘PR22D89’, when both weed free and with weeds. These results have direct implications for weed and nutrient management in low-input and organic cropping systems.     

Dry Matter Production and Productivity as Influenced by Staggered Sowing of Mustard Intercropped at Different Row Ratios with Chickpea

In a 2‐year experiment on Typic Ustochrept soils of the North Plain Zone of India, the effect of different row ratios (3 : 1, 6 : 2, 4 : 1 and 8 : 2) and staggered sowing of mustard (simultaneous and 15 days later) was studied in intercropping of chickpea (Cicer arietinum) and mustard (Brassica juncea L.). Nodule number, dry weight, grain yield, protein content and yield were higher in monocrop chickpea compared with intercropping. Among row ratios, except for protein content in grain, all the above parameters were significantly higher in the 4 : 1 intercropping of chickpea + mustard. Similarly, delayed sowing of mustard by 15 days also gave higher plant dry weight (1.80–2.36 g plant^?1), nodule number (0.41–1.56 and 0.5–3.0 at 55‐ and 70‐day stages, respectively), protein yield (63 kg ha^?1), grain yield (290 kg ha^?1) and biological yield (1104 kg ha^?1) than sowing with chickpea. Widening the row ratio and pairing of the rows of mustard were also found to be beneficial in increasing chickpea growth and yield. Like chickpea, sowing of mustard as a monocrop gave higher growth and yield. Delayed sowing by 15 days reduced the growth and yield of mustard drastically. Productivity, measured in terms of land equivalent ratio, was higher for intercropping of chickpea and mustard in the 4 : 1 row ratio than for sowing of chickpea and mustard in sole stands. Interestingly, the land equivalent ratio was also higher in the simultaneously sown crop than for staggered sowing.     

Effect of Alley Cropping on Crops and Arthropod Diversity in Duzce, Turkey

The influence of alley cropping practices on trees, agricultural crops and arthropod diversity was studied in Duzce, Turkey. Six replications of three crops, maize (Zea mays L. var. rugosa), beans (Phaseolus vulgaris L.) and zucchini (Cucurbita pepo L.), were planted in the alleyways between rows of hybrid poplar [Populus euramericana (Dode) Guinier] in a plantation setting. Control plots included a poplar plot without crops and the three crops planted in plots without trees near the plantation. Sweep netting, sticky traps, pitfall traps, and cloth shaking were used four times throughout a growing season to sample arthropods in the research area. Alley cropping practices had both negative and positive effects on crop yield and a significant negative effect on poplar growth. A total of 10 284 arthropod specimens (15 orders and 122 families) were collected, 118 families in the agroforestry plots, 57 families in the treeless plots and 44 families in the poplar control plot. Diversity indices did not differ among plots, except for the Shannon index, for all dates and sampling methods combined. Evenness indices and family richness measures did not differ significantly among plots, but significant differences were found among collection dates and sampling methods. The tree canopy had a greater arthropod diversity than the ground vegetation. Beneficial arthropods were found in significantly greater numbers in the agroforestry plots compared to the monocrop plots. This suggests that trees provided a more favourable habitat for beneficial arthropods than herbaceous plants. We conclude that agroforestry may contribute to increasing arthropod diversity compared with monocrops.     

Dry matter yield,nitrogen content,and competition in pea–cereal intercropping systems

Intercrops of pea (Pisum arvense L.), a popular legume used in intercropping systems with winter cereals for forage and silage production, with wheat (Triticum aestivum L.), rye (Secale cereale L.), and triticale (× Triticosecale Wittmack) in two seeding ratios (60:40 and 80:20) were compared with monocrops of pea and cereals for two growing seasons. Growth rate, dry matter yield, and N uptake were determined in each intercropping system. Furthermore, several indices were used to evaluate the intercropping systems and analyze the competition and the interrelationships between mixture components. Growth rate of cereals was lower in the mixtures than in the monocrops. Dry matter yield was higher in triticale monocrop, followed by its two intercrops, and the pea–wheat 80:20 intercrop. Moreover, triticale monocrop, pea–triticale intercrops, and pea–wheat 80:20 intercrop showed the highest crude protein yield and N uptake. The land equivalent ratio (LER), relative crowding coefficient (K), actual yield loss (AYL), and system productivity index (SPI) values were greater for the pea–triticale mixtures and the pea–wheat and pea–rye mixtures (80:20), indicating an advantage of intercropping. In most intercrops, the values of partial K, AYL, aggressivity, and competitive ratio (CR) indicated that the cereal was more competitive than pea. The highest values of monetary advantage index (MAI) and intercropping advantage (IA) were recorded for the pea–triticale and the pea–wheat mixtures (80:20). Overall, pea–triticale and pea–wheat mixtures (80:20) were more productive and produced better forage quality than the other mixtures and thus could be adopted by the farmers as alternative options for forage production.     

Direct and Residual Contributions of Symbiotic Nitrogen Fixation by Legumes to the Yield and Nitrogen Uptake of Maize (Zea mays L.) in the Nigerian Savannah

Field experiments were conducted to determine the direct and residual contributions of legumes to the yield and nitrogen (N) uptake of maize during the wet seasons of 1994 and 1995 at the University Farm, Abubakar Tafawa Balewa University, Bauchi, Nigeria, located in the Northern Guinea savannah of Nigeria. Nodulating soybean, lablab, green gram and black gram contributed to the yield and N uptake of maize either intercropped with the legumes or grown after legumes as a sole crop. Direct transfer of N from the nodulating soybean, lablab, green gram and black gram to the intercropped maize was 24.9–28.1, 23.8–29.2, 19.7–22.1 and 18.4–18.6 kg N ha^–1, respectively. However, the transfer of residual N from these legumes to the succeeding maize crop was 18.4–20.0, 19.5–29.9, 12.0–13.7 and 9.3–10.3 kg N ha^–1, respectively. Four years of continuous lablab cropping resulted in yields and N uptake of the succeeding maize crop grown without fertilizer N that were comparable to the yields and N uptake of the succeeding maize crop supplied with 40–45 kg N ha^–1 and grown after 4 years of continuous sorghum cropping. It may therefore be concluded that nodulating soybean, lablab, green gram and black gram may be either intercropped or grown in rotation with cereals in order to economize the use of fertilizer N for maize production in the Nigerian savannah.