Recommended Planting Density Research Articles

Annual Weeds Suppression and Oat Forage Yield Responses to Crop Density Management in an Oat-Cultivated Grassland: A Case Study in Eastern China

Although weeds can be inhibited by high planting densities, canopy shading, elemental balance and soil microbial recruitment are not yet adequately considered when measuring competitive effects on weed control. The effects of oat (Avena sativa) planting density (60 to 600 plants m−2) on the biomass and shoot element balance of oat and weeds were evaluated in a field experiment. The shift in the microbial community of the dominant weed species was examined in a pot experiment by growing the weed alone and in competition with 360 oat plants m−2 (recommended planting density) under greenhouse conditions. Increasing oat planting density beyond 360 plants m−2 did not improve oat forage yield or weed suppression. Compared to 60 plants m−2, the biomass of broadleaf and grass weeds decreased by 1122% and 111%, respectively, at a density of 360 plants m−2, while oat forage biomass increased by 60% and leaf area index by 24%. The improved canopy properties suppressed competing weeds through increased shading. Typically, the C:N and C:P ratios of shoots of Echinochloa crus-galli and Digitaria sanguinalis were higher than those of Portulaca oleracea and Chenopodium album. At high planting densities, E. crus-galli and D. sanguinalis exhibited high P contents and low N:P ratios, suggesting a limited supply of N nutrients for growth. Soil bacterial community assay showed that the composition of microbial communities of the two grass weeds were shaped by the presence of oat competition, which also considerably depleted several important functional microbes associated with nutrient cycling in the weeds’ rhizosphere. These results highlight that increased crop density significantly improves the crop competitive advantage over weeds through increased shading, reduced elemental balance, and beneficial microorganisms of weeds, thereby reducing the need for herbicides or physical weed control in oat cropping system.

Determination of Optimal Plant Density of Adapted Maize Varieties in the Low and Mid-altitude Ecologies of Tanzania

Purpose: The objective of this study is to validate the commonly recommended plant density in the target zone to maximize maize production and productivity. The commonly recommended plant density is 44,444 plants/ha for decades. However, there is no recent study done to validate this practice if it optimizes productivity under current climate and soil fertility variability. A blanket recommendation has been used for decades without validation for optimum productivity that farmer can realize. 
 Methodology: The factorial experiment was used with the total of 18 treatment combinations in a Randomized Complete Block Design (RCBD) with three replications according to Gomez, A and Gomez, K (1983). The open pollinated varieties (OPV) commonly grown by small scale farmers were planted in three different plant densities of 44,444, 53,333 and 66,666 plants per hector with inter and intra row spacings of 0.75mx0.3m, 0.75mx0.25m and 0.75mx0.2m respectively. Field management was done as usual following the recommended agronomic practices.
 Findings: Analysis of variance (ANOVA) was done using GENSTAT (9th edition) statistical programme software and presented in a tabular form. The results indicated no significant difference in all parameters analysed except for 50% anthesis days (AD) and 50% Silking days (SD) both at 0.1% levels. The overall site mean for grain yield was found to be 6.43t/ha, 7.31t/ha and 6.11t/ha for the plant density of 44,444plants/ha, 53,333plants/ha and 66,666plants/ha respectively. Therefore, based on these findings the optimum plant density was found to be 53,333/ha unlike the commonly used plant density of 44,444 plants/ha.
 Unique Contribution to Theory, Practice and Policy: This study contributes to existing experience and practice commonly recommended by extension officers in many parts of the country without performing a site-specific study to determine the optimum spacing for particular environment. This, study also open up an avenue for further research to validate various research technologies. Plant population, in addition to plant height, maturity class, and row spacings, affects the geometry of plant spacing and leaf distribution. All these factors may affect light and CO2 penetration in the canopy, as well as water use rate (Tharp, B and Kells, J, 2001)

Growth and grain yield of canola overseeded on soybean

The overseeding technique allows the establishment of a crop before the harvest of an overseeded crop at the end of the cycle. It aims at making a better use of more favorable seasonal climatic conditions and the intensification of cultivation systems, with the possibility of obtaining another harvest in less time. This work aimed to verify if it is possible to establish the Brassica napus crop in overseeding with the phenological stages at beginning of grain filing (R5) and beginning of soybean physiological maturation (R7) in the Central region of the state of Rio Grande do Sul. The study was performed in a Humid Subtropical climate, in Santa Maria, RS. A randomized block design was used, in a 4 x 2 factorial arrangement with 4 replications, with four seed Brassica napus densities (3, 6, 12, and 18 kg ha-1) and two developmental stages of the soybean crop (R5 and R7), in addition to the control treatment sown in rows directly on the straw right after soybean harvest (3 kg ha-1- standard). The plant density, yield components, and grain yield were measured. The canola crop is not established when overseeded in the soybean stage R5. The seed density of 6 kg ha-1 achieved the recommended plant density for the canola overseeded in stage R7 of the soybean crop. The 6 kg ha-1 density stood out as the best treatment performed in the R7 stage of the soybean crop.

EFFECT OF SOME AGRICULTURAL PROCESS ON GROWTH AND YIELD OF SORGHUM (Sorghum bicolor L.) (ARTICLE REVIEW)

Sorghum is one of the important cereal crops and its importance is due to its multiple uses, as it is used in human food and animal feed in the form of concentrated grains or green fodder, as well as entering into many industries such as starch, cellulose, alcohol, brooms, baskets and many handicrafts and others. Sorghum is the most drought-tolerant summer field crop, but it is one of the crops that stresses the soil as a result of depleting many nutrients, especially nitrogen. Therefore, fertilization is necessary, especially nitrogen, which is reflected in improving the quality of forage and increasing the dry matter yield .The growth and yield of sorghum is affected by many environmental, genetic and agricultural factors, in which the growth and yield are the sum of the effect of these factors combined, and that following modern methods in serving this crop is one of the main factors in improving yield productivity, and the most important of these factors is determining the best cultivar and optimal planting date and the recommended plant density and the best fertilization rate that gives the best yield and the least cost and damage.

Effects of nitrogen application strategy and planting density optimization on sorghum yield and quality

AbstractNitrogen and planting density are two key factors affecting sorghum [Sorghum bicolor (L.) Moench] yield. In this study, two dwarf sorghum cultivars were used to analyze the effects of nitrogen and planting density on the yield and quality of sorghum in northern China. The experiment adopted a two‐factor, split‐zone design with the main plots assigned to three nitrogen application strategies, including all nitrogen applied at the sowing stage (N1), one‐third nitrogen applied at the sowing stage and two‐thirds nitrogen applied at the jointing stage (N2), and all nitrogen applied at the jointing stage (N3). The subplots were assigned to four planting densities of 20 × 104 (D1), 25 × 104 (D2), 30 × 104 (D3), and 35 × 104 plants ha−1 (D4). The results showed that N2 improved significantly the leaf area index, chlorophyll content, and net photosynthetic rate, and the number of grains per panicle and yield were significantly higher than that of the N1 and N3 treatments. Under the same density, the N2 and N3 increased the plant height. Under the same nitrogen, D3 significantly increased the yield. The combination of density and nitrogen was significantly correlated with grain number per panicle and yield. The protein content increased, and the starch content decreased by applying N3 at the jointing stage. The grain yields and grain number per plant were significantly affected by nitrogen application strategy, planting density, and their interaction. The N2D3 was the recommended planting density and nitrogen combination.

Assessment of sowing dates and plant densities using CSM-CROPGRO-Soybean for soybean maturity groups in low latitude

AbstractCrop models can be used to explain yield variations associated with management practices, environment and genotype. This study aimed to assess the effect of plant densities using CSM-CROPGRO-Soybean for low latitudes. The crop model was calibrated and evaluated using data from field experiments, including plant densities (10, 20, 30 and 40 plants per m2), maturity groups (MG 7.7 and 8.8) and sowing dates (calibration: 06 Jan., 19 Jan., 16 Feb. 2018; and evaluation: 19 Jan. 2019). The model simulated phenology with a bias lower than 2 days for calibration and 7 days for evaluation. Relative root mean square error for the maximum leaf area index varied from 12.2 to 31.3%; while that for grain yield varied between 3 and 32%. The calibrated model was used to simulate different management scenarios across six sites located in the low latitude, considering 33 growing seasons. Simulations showed a higher yield for 40 pl per m2, as expected, but with greater yield gain increments occurring at low plant density going from 10 to 20 pl per m2. In Santarém, Brazil, MG 8.8 sown on 21 Feb. had a median yield of 2658, 3197, 3442 and 3583 kg/ha, respectively, for 10, 20, 30 and 40 pl per m2, resulting in a relative increase of 20, 8 and 4% for each additional 10 pl per m2. Overall, the crop model had adequate performance, indicating a minimum recommended plant density of 20 pl per m2, while sowing dates and maturity groups showed different yield level and pattern across sites in function of the local climate.

Optimum plant stand and nutrient doses for summer groundnut under check basin irrigation and drip fertigation in light black soils of peninsular Western India

A field experiment was conducted at Research Farm of ICAR-Directorate of Groundnut Research, Junagadh for consecutive three summer seasons of 2013, 2014, and 2015 with the objectives of identifying optimum plant density and nutrient doses under check basin irrigation and drip fertigation for higher productivity and net returns. The treatments were; three plant densities viz., 3,33,333 plants/ha (100% of recommended plant density; P1); 4,16,666 plants/ha (125% of recommended plant density; P2), and 4,99,999 plants/ha (150% of recommended plant density;P3) in main plots, and three nutrient doses viz., 18.75–37.5–22.5 NPK kg ha−1 (75% of recommended nutrient dose; F1), 25-50-30 NPK kg ha−1 (100% of recommended nutrient dose; F2), and 31.25–62.5–37.5 NPK kg ha−1 (125% of recommended nutrient dose; F3) in sub-plots, and replicated thrice. The same sets of treatments were tested under both check basin irrigation and drip fertigation. The data were analyzed using split plot design. Pod yield, haulm yield, and net returns were significantly higher with P3 as compared to P1 under check basin irrigation but only haulm yield was found significantly higher with P3 under drip fertigation. Under check basin irrigation, NH4–N, NO3–N, and available P and K in soil were found in the order P1 > P2 > P3 (p < 0.05) while in case of drip fertigation, differences were significant only for available K which was significantly higher in P1 over both P2 and P3. Under check basin irrigation, F2 i.e., application of 100 percent of recommended nutrient doses, being at par with F3, significantly improved pod yield, haulm yield and net returns over that with F1 however, differences were not significant under drip fertigation. NH4–N, NO3–N and available P and K in soil under both the irrigation systems were in the order F3 > F2 > F1 (p < 0.05).

Changing Plant Architecture and Density can Increase Chickpea Productivity and Facilitate for Mechanical Harvesting

Tall and erect chickpea cultivar HC 5 (Haryana Chana 5) was primarily bred for inter-cropping with autumn planted sugarcane. Cultivar HC 5 is distinctly different in morphology from traditional bushy or semi-spreading chickpea cultivars and it is found suitable for machine harvesting. However, a general recommended planting density (30 cm × 10 cm) is being followed for cv. HC 5 as well. In this study, we hypothesized that high-density planting can improve crop productivity and also improve the plant architecture for mechanical harvesting. To test this hypothesis, four plant spacing treatments (30 cm × 10 cm, 30 cm × 7.5 cm, 22.5 cm × 10 cm, and 22.5 cm × 7.5 cm) were evaluated in two chickpea cultivars (HC 5 and JAKI 9218) for crop growth, grain yield and the desirable plant traits for mechanical harvesting. The highest grain yield of cv. HC 5 was observed with 22.5 cm × 10 cm spacing that increased the grain yield by 9% (p < 0.05) over plant spacing of 30 cm × 10 cm (conventional); this indicates that high-density planting could increase the productivity of the cv. HC 5. Where grain yield of cv. JAKI 9218 was reduced (p < 0.05) with the increase in planting density over 30 cm × 10 cm. Increased grain yield of cv. HC 5 with 22.5 cm × 10 cm spacing over 30 cm × 10 cm was mainly attributed to increase in plant density (33%); however, all the plant attributes (primary branch, secondary branch, pod plant−1) were reduced as compared to plant spacing of 30 cm × 10 cm. The decrease in intra-row spacing of cv. HC 5 resulted in a strong adverse effect on plant growth and yield parameters as compared to inter-row spacing and thus not recommended. High-density planting increased the plant height (erectness) and ground clearance of cv. HC 5 (height of first pod) (~ 30 cm), an essential prerequisite for mechanical harvesting, but not in cv. JAKI 9218. Hence, cv. HC 5 requires a dense planting for higher yield and appropriate plant structure for mechanical harvesting. Therefore, it is recommended to work out the optimum planting geometry/plant population to realize the potential yield of cultivars bred for mechanical harvesting.

Planting density affected biomass and grain yield of maize for seed production in an arid region of Northwest China

Field experiments were conducted from 2012 to 2015 in an arid region of Northwest China to investigate the effects of planting density on plant growth, yield, and water use efficiency (WUE) of maize for seed production. Five planting densities of 6.75, 8.25, 9.75, 11.25 and 12.75 plants/m2 were conducted in 2012, and a planting density of 14.25 plants/m2 was added from 2013 to 2015. Through comparison with the AquaCrop yield model, a modified model was developed to estimate the biomass accumulation and yield under different planting densities using adjustment coefficient for normalized biomass water productivity and harvest index. It was found that the modified yield model had a better performance and could generate results with higher determination coefficient and lower error. The results indicated that higher planting density increased the leaf area index and biomass accumulation, but decreased the biomass accumulation per plant. The total yield increased rapidly as planting density increased to 11.25 plants/m2, but only a slight increase was observed when the density was greater than 11.25 plants/m2. The WUE also reached the maximum when planting density was 11.25 plants/m2, which was the recommended planting density of maize for seed production in Northwest China.

Influence of nitrogenous fertilizer levels, planting density and IDM on severity of sheath blight of rice caused by Rhizoctonia solani Kuhn in northern Karnataka

The study was conducted to know the influence of nitrogenous fertilizer levels, planting density and integrated disease management (IDM) on the severity of sheath blight of rice in northern Karnataka. The results indicated that, application of 200 kg N per ha recorded higher per cent disease index (PDI) of 40.37 per cent. However, increased N application from 100 kg N to 350 kg N per ha resulted in increased PDI from 17.04 to 62.60%, respectively. Minimum PDI (23.33%) and higher grain yield (67.80 q/ha) were recorded at 150 kg N per ha which is the recommended N dosage in Thunga Bhadra Project command area of Karnataka state. Among different planting densities, the system of rice intensification (SRI) method (16 hills/m 2 ) recorded least PDI (5.00%) and highest grain yield (67.16 q/ha) whereas increased planting density from 20 to 70 hills per m 2 resulted in higher PDI from 6.86 to 45.18 per cent, respectively. However, at 50 hills per m 2 , 16.12 PDI was recorded with a grain yield of 60.53 q per ha which is the recommended planting density. In the integrated disease management (IDM) trial, wherein, use of cultivar, IR-64 (moderately resistant variety) with foliar application of fungicide hexaconazole (@0.1%) resulted in minimum PDI of 21.26% with higher grain yield of 71.74 q per ha as against 34.73 PDI and 56.87 q per ha grain yield in Samba mahsuri (susceptible variety).

Performance of Miscanthus x giganteus (Greef et Deu) established with plastic mulch and grown from a range of rhizomes sizes and densities in a cool temperate climate

The effect of biodegradable plastic mulch, rhizome size and planting density on establishment, annual harvested biomass yield of miscanthus and nutrient content were studied at two sites in Northern Ireland. In a split plot experimental design plastic mulch treatment was applied randomly to main plots (covered or left uncovered) after planting rhizome fragments varying in size (by weight) and planting density which were assigned randomly to subplots in four replicated blocks, at each site.Mean shoot density over both sites was 7.8 and 12.6m−2 for unmulched and mulched in October of the establishment year. Averaged over all sites and planting treatments, uncovered total biomass yields were 0.47, 4.79, 7.74 and 8.12tDMha−1, for the first four annual spring harvests, respectively, mulch increasing these yields by 68, 49, 36 and 24%, respectively. Although there were significant effects of rhizome size and density, the effect of plastic declined at successive harvests for large and medium sized rhizomes and high and standard densities. The main effect of plastic mulch was to increase the shoot population density, and shoot number per plant, especially in plants from rhizomes planted at a low number per unit area. Although there were soil moisture deficits in some months, mulching was considered to have improved yields mainly by increasing shoot density due to higher soil temperatures during establishment followed by a mild winter. By the third year, plastic mulch had no significant effect on recommended planting density at all harvests. Plastic mulch had no marked effect on content of N, P or K in biomass.Covering miscanthus rhizomes with a biodegradable plastic mulch is an effective management tool to increase miscanthus biomass production in a cool temperate climate, at least in the first 3–4 years of production. This is mainly due to increase in soil temperature during establishment and the subsequent year. Mulching allows the optimum planting density of rhizomes to be reduced. Despite additional cost plastic mulch represents an economic benefit to the crop.

Root development and whole-tree allometry of juvenile trees of five seed lots of Pinus radiata D.Don: implications for forest establishment on erosion-prone terrain, East Coast region, North Island, New Zealand

Establishment of exotic forest on erosion-prone pastoral hill country in the East Coast region of New Zealand escalated following a major cyclonic storm in 1988. Pinus radiata D.Don is the predominant species used for erosion control. It has been suggested that planting densities could be reduced if faster growing P. radiata seedlings and cuttings from genetically improved seed lots were used. A field-based trial was established to measure and compare annual growth rates between P. radiata seed lots (GF 16 and GF 19 seedlings and cuttings grown from GF 23 seed) used during the period of early forest establishment (1960s onwards) in this region and genetically improved seed lots (GF 27 seedlings and GF 28 cuttings) developed at a later date. Over a 4-year period, the above-ground parameters (diameter at breast height, root collar diameter, tree height and canopy diameter) were measured before whole trees (canopy and root systems) were destructively sampled. Root collar diameter (over bark) was most highly correlated with tree height, with r 2 ranging between 0.95 and 0.98 for all the seed lots, and all regressions were highly significant (P < 0.001). In any year of the trial, there were no differences among seed lots with respect to root collar diameter, total above-ground biomass or total below-ground biomass. By year 4, mean below-ground biomass comprised 17% of total biomass. There was no consistently significant difference among seed lots in the distribution of total below-ground biomass or root length with distance from the root bole, relative to depth, or in either their maximum lateral root spread or maximum root depth until year 4 when GF16S and GF27S had a greater (P = 0.05) maximum root spread than GF28C while the latter had developed a significantly greater (P = 0.05) proportion of its root biomass and root length within the top 0.5 m of the soil profile. The root cross-sectional area of vertical roots increased significantly with age but decreased with depth. Root orientation formed a ‘bilateral fan-shaped’ architecture. The absence of consistently significant differences among seed lots suggests that during the early 4 year post-establishment period, no one seed lot would provide earlier soil reinforcement or result in a superior level of slope stability than would any of the other seed lots trialled. Thus, irrespective of seed lot preferences, any reduction in the current recommended planting density for erosion-prone hill country would further increase the period of vulnerability and risk of young plantings to damage by storm-initiated landslides.

Changes in spring wheat (Triticum aestivum ssp. vulgare L.) and persian clover (Trifolium resupinatum L.) biomass under the influence of plant competition and density

The influence of sowing method and plant density on the biomass of spring wheat and Persian clover was evaluated. In a pot experiment conducted in three series during the years 2010–2012, plants were cultivated as mixed and pure crop at higher (consistent with agronomic recommendations) and lower density, decreased by 20% compared to it. Dry mass accumulation tests for both species were conducted during the following wheat growth stages (BBCH): leaf development (12–14), tillering (21–23), stem elongation (31–32), inflorescence development (54–56), and ripening (87–89). Based on the results obtained, the biomass growth rate for both species in question was also determined. It was shown that the mass of shoots of spring wheat cultivated as mixed crop was lower than that of wheat shoots grown as pure crop during the stem elongation and ripening stages. Mixed sowing limited aboveground accumulation in the heads and grain the most and in the stems the least. During the leaf development and stem elongation stages, the wheat presented a more pronounced response to the presence of clover expressed by biomass decrease in case of the treatment with lower plant density and during ripening in the treatment with recommended plant density. In case of both sowing methods and plant densities, the mass of wheat roots was similar. Biomass accumulation in Persian clover shoots and roots in mixed sowing was lower than in pure crop during the entire growing period. The wheat limited biomass accumulation of Persian clover in inflorescences the strongest and in the roots the least. The spring wheat growth rate in both sowing methods was similar as opposed to Persian clover in the case of which a decrease in the growth rate was observed in the mixed crop during the generative development period.

Effect of Planting Density on the Performance of Hybrid Rice (Oryza sativa L.) under Waterlogged Condition

The experiment was conducted to find out the effect of planting density on the performance of hybrid rice variety Aloran under water logged condition at the BRAC Agricultural Research and Development Center in Gazipur, Bangladesh during the dry (DS) and wet season (WS) of 2009. Different planting densities were maintained using different spacings and number of seedlings per hill. These include 25 cm × 20 cm, 25 cm × 10 cm, 20 cm × 10 cm, 20 cm × 15 cm with single seedling per hill and 20 cm × 15 cm with two seedlings per hill and 20 cm × 15 cm with three seedlings per hill. The experiment was laid out in a randomized complete block design with 3 replications. Density of 20 cm × 10 cm with 1 seedling hill-1 i.e. 50 hills m-2 produced the highest grain yield of 7.5 t ha-1 and 4.6 t ha-1 in DS and WS respectively, which was significantly higher than the yield with recommended density (20 cm × 15 cm with 1 seedling per hill). This yield was increased due to higher number of panicles m-2. Increasing the seedling numbers hill-1 with the recommended planting density did not improve the yield of hybrid rice. This result suggests that higher planting density rather than increased number of seedling hill-1 is necessary for getting higher yield of hybrid rice in continuous water logged condition. DOI: http://dx.doi.org/10.3329/agric.v11i2.17497 The Agriculturists 2013; 11(2) 109-113

Rubber latex production in Hevea brasiliensis with high density planting

Despite short-term fluctuation of rubber prices, the demand of natural rubber has increased continuouslywith the increase in population and living standards of the human being. Nevertheless, urbanizationresults in the fast depletion of forests as well as the land area under rubber. Therefore, in order tomeet the continuous demand on latex, the productivity of rubber plantations should be increased.While producing high yielding clones for improved yield per tree which is a long-term process inperennial crops, planting density could be adjusted to obtain high productivity in rubber plantations.The present level of planting density of rubber in Sri Lanka has been decided on the experimentsconducted with the genotypes which are not in common use at the moment. Also, the optimum densityshould vary with different socio-economic conditions. Therefore, the present study was aimed toidentify the suitable planting density for the recently developed and commonly used genotypes of rubber. Specifically, this paper is focused to assess the overall productivity of rubber with respect tolatex yield.The experiment was set up in Rathnapura district of Sri Lanka in 1992. Rubber was planted in threehigh densities, i.e., 600, 700, 800 trees per hectare, with the presently recommended level of500 treesper hectare. Also, 3 genotypes (clones) i.e., RRIC 100, RRIC 110 and RRIC 121 were incorporatedwith the statistical design of split plot where the planting densities were laid as the main plots whilstclones were in the sub plots. Growth and yield parameters in terms of girth, bark thickness (8T), andthe incidences of tapping panel dryness (TPD) were assessed yearly and the latex volume (LV), %dry rubber content (DRC), number of trees in tapping (TIT) were assessed on daily basis up to 2004.Irrespective of the clone used, mean yield per tree per tapping decreased with increase in plantingdensity. However, it was vice versa in the case of yield per hectare (YPH) due to the increase in TITwith increase in planting density. The percentage of trees with 'fPD was not significantly affected bythe planting density. The clone RRIC 110 was infected with Coryncspora leaf disease hence poorperformance was shown in all densities. The trend of increasing YPH was similar in both otherclones. i.c. RRIC 100 and RRIC 121. However, the rate of increase in TIT showed a decline of700trees per hectare resulting in a lower YPII at this level than expected. Although latex productivitycould generally be increased with increase in planting density, overall economic profitability of thesystem wi II also depend on cost of production, amount and va lue or tim bel' and carbon produced.Therefore, study warrants further investigations on above issues before making any changes to thepresently recommended planting density.

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.

Basal branching in field pea cultivars and yield-density relationships

The current recommended plant density in field pea (Pisum sativum L.) in western Canada is 88 plants m–2. This rate may exceed the optimum for yield in cultivars with more basal branching than typical. The objective of this research was to determine how the seed yield of pea cultivars differing in basal branching ability responds to changes in plant density. Ten pea cultivars were sown at target plant populations of 10, 30, 90, 120, and 150 plant m–2 for 3 yr at Rosthern and Saskatoon, Saskatchewan. At very low plant densities there was greater than a twofold difference in branching potential between cultivars (range 0.85 to 1.99 branches plant–1). Increasing field pea plant density reduced branching by 0.097 branches for each additional plant. The response of yield to plant density differed, as the forage cultivars 40-10 and CDC Sonata reached their potential yield at lower densities, while Courier required higher densities to reach the same proportion of yield. Field pea cultivars with greater basal branching achieved their maximum yield at lower plant densities compared with cultivars with low basal branching. The optimum economic plant density for the pea cultivars ranged from 59 to 84 plants m–2, which is below the current recommended plant density. However, with the exception of the forage cultivars and the low-branching cultivar Courier, the optimum seeding rate was within 8% of 88 seeds m–2. It is recommended that pea growers avoid low-branching pea cultivars and seed at a rate of 88 viable seeds m–2.Key words: Basal branching, seeding rate, plant density, light interception, leafed pea, semi-leafless pea, forage pea

Pea–barley intercropping for efficient symbiotic N 2-fixation, soil N acquisition and use of other nutrients in European organic cropping systems

Complementarity in acquisition of nitrogen (N) from soil and N 2-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 N 2-fixation. At all sites the proportion of total aboveground pea N that was derived from N 2-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 N 2-fixation inputs to the cropping system.

Pea–barley intercropping and short-term subsequent crop effects across European organic cropping conditions

Grain legumes are known to increase the soil mineral nitrogen (N) content, reduce the infection pressure of soil borne pathogens, and hence enhance subsequent cereals yields. Replicated field experiments were performed throughout W. Europe (Denmark, United Kingdom, France, Germany and Italy) to asses the effect of intercropping pea and barley on the N supply to subsequent wheat in organic cropping systems. Pea and barley were grown either as sole crops at the recommended plant density (P100 and B100, respectively) or in replacement (P50B50) or additive (P100B50) intercropping designs. In the replacement design the total relative plant density is kept constant, while the additive design uses the optimal sole crop density for pea supplementing with ‘extra’ barley plants. The pea and barley crops were followed by winter wheat with and without N application. Additional experiments in Denmark and the United Kingdom included subsequent spring wheat with grass-clover as catch crops. The experiment was repeated over the three cropping seasons of 2003, 2004 and 2005. Irrespective of sites and intercrop design pea–barley intercropping improved the plant resource utilization (water, light, nutrients) to grain N yield with 25–30% using the Land Equivalent ratio. In terms of absolute quantities, sole cropped pea accumulated more N in the grains as compared to the additive design followed by the replacement design and then sole cropped barley. The post harvest soil mineral N content was unaffected by the preceding crops. Under the following winter wheat, the lowest mineral N content was generally found in early spring. Variation in soil mineral N content under the winter wheat between sites and seasons indicated a greater influence of regional climatic conditions and long-term cropping history than annual preceding crop and residue quality. Just as with the soil mineral N, the subsequent crop response to preceding crop was negligible. Soil N balances showed general negative values in the 2-year period, indicating depletion of N independent of preceding crop and cropping strategy. It is recommended to develop more rotational approaches to determine subsequent crop effects in organic cropping systems, since preceding crop effects, especially when including legumes, can occur over several years of cropping.

Effect of maize planting density on the performance of maize/soybean intercropping system in a guinea savannah agroecosystem

Two field experiments were conducted during the 2004 early and late seasons at the Agricultural Vocational Training Centre, Otobi, Otukpo in the southern guinea savanna agro-ecological zone of Nigeria to evaluate the effects of maize planting density (38,000; 44,440 and 53,330 plants/ha) in intercrop with soybean varieties (TGX 1448-2E and Samsoy-2) on the growth, yield and productivity of the maize/soybean intercropping system. The soybean varieties were maintained at the optimum planting density of 266,660/ha in both sole and intercrops while sole maize (TZR-EW) plots were at the recommended planting density of 53,330 plants/ha. Samsoy -2 soybean plants were taller at the various ages of growth, had more leaves and attained 50% flowering earlier, produced more and heavier nodules than TGX 1448-2E but TGX 1448-2E produced significantly (P < 0.01) more pods and higher seed yield in both seasons. Intercropping reduced the number of soybean pods per plant by 46% in the early season and seed yield by 42 and 46% in the early and late seasons, respectively. Increasing maize planting density reduced soybean seed yield by 21 and 23% at maize planting density of 44,440 and 53,330 plants/ha, respectively, compared with intercropping at 38,000 maize plants/ha. Maize plant height and leaf production were not influenced by intercropping nor by maize planting density but in the late season, maize grain yield was highest with 53,330 maize density/TGX 1448-2E but lowest with 38,000 maize density/Samsoy-2 cropping. The productivity of the intercropping system indicated yield advantage of 2-63% as depicted by the LER 0f 1.02-1.63 showing efficient utilization of land resource by growing the crops together and this increased with maize planting density. The total monetary return was higher for the intercrops than the sole crops with the values highest with 53,330 maize density/TGX 1448-2E in both early (N293,171.80) and late (283,069.70) seasons. The implication of this is that farmers in the study area would earn more income growing the crops together. Key words: Maize planting density, soybean, intercropping, land equivalent ratio, monetary return.