Complete Ground Cover Research Articles

Hybrid brachiariagrass (Urochloa spp.) establishment with annual sorghum sudangrass (Sorghum bicolor (L.) Moench) and sunn hemp (Crotalaria juncea L.) mixtures at half and full recommended seeding rates

AbstractThe slow initial growth of hybrid brachiariagrass (Urochloa spp.) can require some months to achieve complete ground cover of a newly seeded area, leading to decreased forage production and increased weed infestation in the establishment year. To solve these problems, we attempted to sow seeds by mixing warm‐season annual forages with brachiariagrass at a brachiariagrass pasture establishment (University of Florida, USA, 2017 and 2018). Treatments were single seeding of ‘Cayman’ brachiariagrass solo (BR), sorghum sudangrass solo (Sorghum bicolor (L.) Moench; SD), and sunn hemp solo (Crotalaria juncea L.; SH) and two mixtures of these three forages at half (HSR) or full (FSR) of the recommended seeding rate. The seeding rates of FSR were, respectively, 10, 20, and 25 kg/ha for brachiariagrass, sudangrass, and sunn hemp. The treatments were distributed in a randomized complete block design with four replicates. Plots were harvested at 6, 12, 18, and 24 weeks after seeding. The number of brachiariagrass seedlings in the HSR and FSR treatments was less than half that in the BR (P < .05). The BR treatment had greater brachiariagrass herbage accumulation (HA) at all harvests than HSR (4%–75% of BR) or FSR (7%–66% of BR). This difference between the BR and mixture treatments became narrower in later harvests. In addition to the decreased number of brachiariagrass seedlings, light and nutrient competition between annual forages are considered to be the causes of lower brachiariagrass HA in the mixture treatments. Sunn hemp increased forage HA and crude protein concentrations at 6 weeks. Sudangrass provided overyielding forage until 18 weeks after seeding, with a similar nutritive value as brachiariagrass. Mixing warm‐season annual forages with brachiariagrass at the establishment, especially half of the seeding rates of sunn hemp and sudangrass, is a feasible management practice to increase HA during the first 12 weeks after seeding.

Autonomous Mowing and Turf-Type Bermudagrass as Innovations for An Environment-Friendly Floor Management of a Vineyard in Coastal Tuscany

The establishment of permanent cover crops is becoming a common practice in vineyard floor management. Turfgrass science may provide species and techniques with a high potential for improving the sustainability of vineyard floor management. Based on this assumption, an experiment was carried out during 2018 and 2019 at the Donna Olimpia Vineyard, Bolgheri, Italy. The trial aimed at comparing an innovative floor management system based on a turf-type cultivar of bermudagrass mown with an autonomous mower with a conventional floor management system. Ground cover percentage, energy consumption, CO2 emissions, grapevine water status, leaf nitrogen content, fruit yield and must composition have been assessed in order to perform the comparison. The innovative vineyard floor management produced an almost complete ground cover (98%) at the end of the second growing season, with the resident species reduced to a small percentage (4%). Resident species growing under-trellis were efficiently controlled without herbicide applications. A lower primary energy consumption and a reduction in CO2 emissions were observed for the innovative management system compared to the conventional management system. Grapevine water status, leaf chlorophyll content, soil–plant analyses development (SPAD), fruit yields and must composition were similar between the different soil management systems. Based on results obtained in this trial, turf-type bermudagrass and innovative mowing machines may contribute to enhance the sustainability of vineyard floor management.

Intercepted radiation and radiation-use efficiency in sunflower crops grown at conventional and wide inter-row spacings: Measurements and modeled estimates of intercepted radiation

The underlying eco-physiological principle behind row spacing choice in many field crops is that early and complete ground cover will maximize yield via greater crop photosynthesis during the critical period for grain number determination in environments with no major water limitations. Recently this principle has been put in doubt: wide row-spacing (1.40 m instead of 0.7 m) did not reduce oil or biomass yield in sunflower at plant densities of between 2 and 7 pl m−2, in spite of incomplete ground cover at the wider row spacing. Here, we report the effect of two row spacings (0.7 and 1.4 m), in sunflower crops of equal plant density, on interception of radiation, radiation use efficiency (RUE), crop biomass and oil yields in three experiments. Two approaches were used to estimate interception of radiation by the crops: i) periodic diurnal measurements during the crop cycle of interception in the inter-row space and on the sides of the hedgerows; and ii) the use of a olive hedgerow model, adapted to sunflower, to estimate radiation intercepted by the two crop arrays. Biomass at anthesis, at physiological maturity, and oil yield in crops grown in the two row-spacings did not differ. The results show that the increased RUE of the 1.4-m spaced crops in pre-anthesis phase was able to compensate for the delay of these crops in achieving close to full interception of irradiance. The daily patterns of irradiance incident on the hedgerow faces, especially the sunlit face, in the pre-anthesis phase and in the early and late hours of the day, were strongly affected by row-spacing. A more favorable irradiance in these periods of the day in the mid- and upper portions of the sunlit face of the 1.4-m spaced hedgerows may have contributed to the greater RUE values of these crops in the pre anthesis phase.The hedgerow model provided descriptions of the seasonal dynamics of intercepted radiation that were fully consistent with measured values for both row spacings.

Erosion mitigation in the Waikato District, New Zealand: economic implications for agriculture

AbstractSoil erosion, in its various forms, is caused or aggravated by agricultural activities. Mitigation of surface erosion comprises the construction of shelterbelts, fencing, riparian buffering, and stock reduction. Mitigation of mass‐movement erosion, in turn, takes the form of spaced planting of trees to maintain a persistent, healthy, and complete ground cover. In this article, we assess the economic implications to agriculture of the adoption of mitigation alternatives for erosion control in the Waikato District, New Zealand. The Waikato District presents a spatial pattern of erosion that affects profitability of dairy, and sheep and beef enterprises. We use the Universal Soil Loss Equation and the New Zealand Empirical Erosion Model to estimate erosion figures that are then fed into an economic‐focused, nonlinear, partial equilibrium mathematical programming model of New Zealand land use. Different scenarios are constructed for surface and mass‐movement soil erosion targets ranging from 0% to 50% below baseline levels. We find that achieving surface erosion targets is more expensive than mass‐movement targets, and results in different responses in regional‐level costs, land use, enterprise net revenue, and adoption of mitigation alternatives.

Diversity and Behaviour of the Naturally Regenerated Vegetation in Commercial Tea Soils Under Herbicide Free Integrated Weed Management

Weed management is essential in agriculture to prevent Economic Crop Damage in farm products due to quality and quantity losses. Herbicides are profusely being used to meet this objective despite their hazardous nature on human health and the environment caused by residual contamination of food and drinking water. Sri Lanka imported 7,967,852kg and 5,675,611kg of Herbicide chemicals in the forms of bulk and ready to use formulations in year 2013 and 2014 respectively and Commercial Tea Plantations too are heavily depend on herbicides to maintain “Clean and Clear Ground Concept” (CCGC) based mind set established in the sector. However, CCGC is not recommended by Tea Research Institute of Sri Lanka due to severe degradation in the tea soils resulted. Many of the so called weed species has the ability to thrive in degraded poor soils forming a quick ground cover arresting further depletion in soil and upgrade same by addition of Organic Carbon as leaf litter and root secretions feeding soil microbes. This study explored the diversity and perennial behaviour of the Natural Vegetative Regeneration (NVR) in Commercial Tea Soil under herbicide-Free Conditions to demonstrate the possibility of practicing Herbicide-Free Integrated Weed Management (HFIWM) in the Tea Industry at commercial scale in Sri Lankan conditions. The survey commenced in Hapugastenne estate Maskeliya Plantations PLC., following to pruning, on a weed free, exposed Tea field in an extent of one hectare, where natural regeneration of vegetation was allowed and monitored, under a Treatment of “Herbicide - Free Integrated Weed Management” (HFIWM), for three years. Non-IWM (Control) area of similar extent was demarcated adjoining to said area and sprayed with Diuron, Paraquat and Glyphosate, as recommended by the Tea Research Institute of Sri Lanka. The naturally regenerated Terrestrial Vegetation in treated and control areas, was surveyed periodically and simultaneously, by investigating 3m X 3m sample plots with four replicates each time, concerning species diversity and recorded the variations observed. Non-IWM section displayed a continuous increase in plant diversity up to 76 species, within three years, dominated by Herbicide tolerant weed species. Vegetation established on HFIWM area reached a peak of 64 plant species within the first year itself, forming a complete ground cover whilst effectively suppressing many of the targeted notorious weeds which cause severe economic damage in Commercial Tea Plantations.

Investigating the influence of roughness length for heat transport (zoh) on the performance of SEBAL in semi-arid irrigated and dryland agricultural systems

Summary Satellite-based thermal infrared remote sensing has greatly contributed to the development and improvement of remote sensing-based evapotranspiration (RS-ET) mapping algorithms. Radiometric temperature (Ts) derived from thermal sensors is inherently different from the aerodynamic temperature (To) required for solving the bulk formulation of sensible heat (H). The scalar roughness length (zoh) representing heat transport mechanism and described by the dimensionless parameter kB−1 was used to account for the discrepancy between Ts and To. Surface Energy Balance Algorithm for Land (SEBAL), with its indigenous approach of linearly relating dT (near-surface temperature gradient) with Ts across the imagery, maintained that this approach would absorb the impacts of differences between Ts and To. Therefore, it utilized a constant kB−1 value of 2.3 in its initial version, and later switched to a constant zoh (z1) value of 0.1. In this study, we investigated the influence of these changes in SEBAL by testing four different approaches: (i) zoh derived from a constant kB−1 of 2.3, (ii) constant zoh (z1) = 0.1 m, (iii) constant zoh (z1) = 0.01 m, and (iv) spatially variable zoh from kB−1 parameterization. SEBAL was applied on 10 high-resolution airborne images acquired during BEAREX07-08 (Bushland Evapotranspiration and Agricultural Remote Sensing Experiment) and validated against measurements from four large weighing lysimeters installed on two irrigated and two dryland fields. The spatially variable kB−1 produced statistically different and improved ET estimates compared to that with constant kB−1 and constant z1 (zoh) approaches. SEBAL performance for irrigated fields representing high ET and complete ground cover surfaces was markedly different from that for dryland fields representing greater soil water deficits with sparser vegetation cover. A variable kB−1 value derived from a physical model generated good overall estimates while delivering improved performance for dryland agricultural systems. Overall, this study focused on the classical problem of estimating heat transfer from two contrasting hydrological regimes i.e. irrigated and dryland agriculture and illustrated the existing need for a realistic consideration of excess resistance to heat transfer in single-source resistance modeling frameworks.

Root distribution and demography in an avocado (Persea americana) orchard under groundcover management systems.

The effect of groundcover management systems on root demography and distribution of newly planted avocado (Persea americana Mill) trees was examined using minirhizotron techniques. We evaluated three groundcover systems: (1) bare soil (BS), pre- and post-emergence herbicides; (2) vegetation strip (VS), post-emergence herbicide applied in a 1-m wide strip centred on the tree row plus a groundcover mixture seeded between tree rows; and (3) complete groundcover (GC), covering the entire surface of the plots. Root production was higher in the non-bearing year (2009-10) than in the bearing year (2010-11). Trees in the BS plots had more roots of bigger diameter in the top 30cm of soil and trees in VS and GC plots had more roots in the 30-60cm depth and of smaller diameter. Lifespan of spring-born roots were 61 and 59% greater than those born during autumn and summer, respectively and soil depth and root diameter were positively correlated with root longevity. Lifespan of thinner roots (<0.2mm) in the BS and VS plots were 49 and 33% greater than GC respectively. Avocado trees grown in contrasting condition compared with their native habitat show high morphological root plasticity, in response to resource and non-resource competition when grown in mixed stands.

Estimating Crop Water Use of Cotton in the Texas High Plains

The growth and yield of cotton (Gossypium hirsutum L.) in the semiarid Texas High Plains is driven by the amount of water available to the crop through rainfall and irrigation. Various methods have been developed for quantifying the crop water use (CWU) of agricultural crops. In this study, we described a method for estimating CWU that uses a modified version of the Penman–Monteith Equation. In this method, CWU is equal to the transpiration of a well‐watered crop with complete ground cover (determined from ambient environmental conditions) multiplied by the amount of plant canopy present (quantified by crop ground cover) and a parameter (Fs) related to the effects of stomatal closure. For irrigated and dryland cotton that are acclimated to their respective environments, Fs ≈ 1. This suggests that control of canopy leaf area is a primary mechanism for acclimating to the surrounding environment. When Fs &lt; 1, the plant is not acclimated with its environment and must rely on stomatal closure to conserve available water in the root zone. The method was developed using surface energy balance data and remotely sensed crop ground cover for three fields near Lubbock, TX. This method could be used in irrigation scheduling where irrigation is used to replace the daily CWU of a crop. This approach might be superior to the standard crop coefficient approach because it could use remotely sensed crop ground cover as a “spectral crop coefficient” that would make the resulting estimates of CWU specific to individual fields.

Delayed Tillage and Cover Crop Effects in Potato Systems

Delayed tillage and the inclusion of cover crops can substantially reduce erosion in intensively tilled potato systems. Both of these practices can potentially impact potato (Solanum tuberosum L.) yield and quality via changes in soil temperature and soil water status, and suppression or enhancement of soil-borne diseases. Research was conducted over six rotation cycles at two Maine locations to evaluate the effects of timing of primary tillage (fall vs. spring) and cover crop [none, red clover (Trifolium pratense L.), ryegrass (Lolium perenne L.), or winter rapeseed (Brassica napus L.)] on grain yield, ground cover, and tuber yield and quality within the context of 2-year barley (Hordeum vulgare L.)]–potato rotations. Delaying primary tillage until spring, immediately before planting potato, resulted in higher soil water content early in the growing season (before or immediately after planting) in some rotation cycles, and also provided nearly complete ground cover during potentially erosive periods in fall and early spring. The inclusion of clover or ryegrass cover crops had small, positive effects on the proportion of the soil surface covered by crop residue (determined by the line intercept method) in both tillage systems. A significant tillage effect on total tuber yield was seen in only one rotation cycle, when delaying tillage until spring reduced yield by about 12%. Cover crop treatments had no effect on total tuber yield, and neither tillage or cover crop affected the proportion of marketable tubers. Tillage did not affect black scurf (Rhizoctonia solani Kuhn) and common scab [Streptomyces scabiei (Thaxter) Lambert & Loria], which were significantly reduced by red clover in some rotation cycles. This research shows that conservation practices can be implemented, including delaying primary tillage until spring and including underseeded cover crops during the grain phase of the rotation, while maintaining potato yield.

Long-term effect of pastures on soil quality in acid soil of North-East India

North-East India is known for its complex, diverse, risk-prone, and fragile hilly ecosystem. Natural resources in terms of soil, water, vegetation, and soil organic carbon (SOC) are much degraded. Effects of long-term perennial grasses maintained at a permanent fodder block of the ICAR Research Complex, Meghalaya, on soil quality were examined after 15 cropping cycles. The aims were (i) to ascertain whether perennial grass primarily maintained as fodder source for ruminants could conserve resources and improve soil quality in the hilly ecosystem of North-East India, and (ii) to select a suitable perennial grass to minimise land degradation, restore SOC, and improve the soil quality. Soil samples were collected in 2007–08 (dry season) from plots of 8 perennial grasses [Setaria sphacelata (setaria), Brachieria rosenesis (congosignal), Thysanolaena maxima (broom), Penicum maximum var. Makunia and var. Hamil (guinea), Pennisetum purpureum (napier), Paspalum conjugalum (paspalam), Arachis pintoi (wild groundnut)] and analysed for physical, chemical, and biological properties. A control plot had no grass cover. Hamil and Makunia produced a large amount of green fodder, while Makunia, paspalam, setaria, and congosignal had greatest root biomass. Relative to the control, soil under perennial grasses showed increases of ~30% SOC, 70% mean weight diameter, 20% available soil water, 40% hydraulic conductivity, 63% infiltration rate, and 10% soil microbial biomass carbon. Among grasses, soil under setaria, congosignal, and Makunia had higher values of these attributes than under other species because of better soil binding through an extensive root system. Improvement of soil physical properties and processes under these grasses, coupled with complete ground cover, reduced soil erosion by ~33% and also signified ecological benefits through C-sequestration. Soil quality management in the fragile ecosystem of North-East India should include permanent pastural grasses, particularly, setaria, congosignal, and Makunia.

Mapping Ground Cover Using Hyperspectral Remote Sensing after the 2003 Simi and Old Wildfires in Southern California

Wildfire effects on the ground surface are indicative of the potential for post-fire watershed erosion response. Areas with remaining organic ground cover will likely experience less erosion than areas of complete ground cover combustion or exposed mineral soil. The Simi and Old fires burned ∼67,000 ha in southern California in 2003. Burn severity indices calculated from pre- and post-fire multispectral imagery were differenced (i.e., differenced Normalized Burn Ratio (dNBR)) to highlight fire-induced changes to soil and vegetation. Aerial and field hyperspectral data were also collected together with field ground cover measurements soon after the fires. Spectral endmembers representing green vegetation, nonphotosynthetic vegetation (NPV), charred NPV, and charred and uncharred inorganic materials (soil, ash, and rock) were used in a constrained linear spectral unmixing process to determine the post-fire fractional ground cover of each component on the ground surface. The spectral unmixing results, dNBR, and a Relative dNBR (RdNBR) were validated using field-measured fractional ground cover estimates to determine which product best predicted the conditions on the ground. The spectral unmixing results were significantly correlated to all classes of charred and uncharred organics and inorganics, and the dNBR was the best indicator of charred soil and green vegetation. The RdNBR had several significant correlations with the ground data, yet did not consistently correlate well with any specific ground cover types. A map of post-wildfire ground cover and condition, especially exposed soil and remaining vegetative cover, is a good indicator of the fire’s effect on the ground surface and the resulting potential for hydrologic response.

Thinking across and beyond disciplines to make cover crops pay

As the name implies, a cover crop consists of plants grown primarily to keep the land covered, especially during the off-season or between cash crops. In temperate regions like most of Europe and North America, a cover crop sown immediately after the main crop harvest in fall is considered a winter cover crop. It will grow in the fall, either subjected to frostkill or go into relative dormancy during the dead of winter, and then, if winter-hardy, recommence growth in very early spring before soils are warm and dry enough for the next cash crop. If the climate is sufficiently mild, such cover crops may produce substantial above-ground dry matter (3000–6000 kg ha−1) and nearly complete ground cover before being terminated. For many decades, the use of cover crops has been promoted mainly to prevent the severe soil erosion that winter and spring rains can bring if soils are left bare. In addition, it is widely recognized that regular use of winter cover crops – as compared to bare fallow over winter – can provide enough carbon input to build – or at least slow the decline of – soil organic matter. For these reasons, many scientists view cover crops as an essential tool in managing farmland for long-term sustainability.1 A considerable amount of cover crop research has been conducted in the mid-Atlantic region of the USA during the past three decades. Most of this research focused on just a handful of cover crop species, mainly cereal rye and hairy vetch, which were found to be well adapted to the region’s climate and cropping systems. With the advent of programs to restore the health of the Chesapeake Bay, most cover crop research in Maryland has been directed towards using cover crops to capture residual mineral nitrogen (N) before it can leach away in the fall. Extensive research on coastal plain soils has demonstrated the ability of a rye cover crop to greatly reduce the loss of N to groundwater from maize grown in no-till production systems.2 However, relatively little has been done to demonstrate direct benefits to the farmer from the use of cover crops. One economic benefit that has been well quantified is the ability of legume cover crops, under some conditions, to replace by biological N2 fixation most or all of the fertilizer N needed for optimal production of nitrogen-demanding crops. However, under realistic conditions, research indicates that it costs about as much to grow and manage a hairy vetch cover crop as the value of the N fertilizer it saves.3,4 While biologically fixed N is likely to become more profitable as the cost of N fertilizer rises, legume cover crops grown alone are not very effective at capturing residual fall N. Although not often discussed by researchers, farmers recognize that growing a cover crop adds extra expense, complexity and uncertainty to the already risky business of farming. Under some circumstances, certain cover crops have interfered with crop production by using up water stored in the soil profile, by immobilizing N needed for the cash crop and by becoming weedy or producing excessive residues, hampering crop stand establishment or harvest. The most obvious direct costs associated with cover crops include those for cover crop seed, labor, fuel, fertilizer and herbicide or tillage to kill the cover crop. Given these considerations, the State of Maryland has for several years paid subsidies of $50–100 per hectare for timely planting of cover crops with a goal of keeping at least 75% of Maryland’s cropland acres under cover crops in winter. Despite this incentive, adoption rates remain relatively low, with only about 20–25% of cropland hectares receiving cover crops. We suspect that this is because most farmers in this region are not sufficiently aware of the direct benefits that cover crops potentially offer, possibly as a result of past research and extension work that emphasized cover cropping’s role in N fixation, environmental protection and long-term soil resource conservation. Although nearly all farmers desire to be good stewards of their land, most face tight (or negative) profit margins and cannot afford to engage in environmental altruism without first considering their operations’ bottom line and efficiency goals. Lacking credible information and examples that might convince them otherwise, many farmers have reached the conclusion that cover crops are simply not worth the cost and trouble.

Interception of photosynthetically active radiation and radiation-use efficiency of wheat, field pea and mustard in a semi-arid environment

Fractional ground cover, fractional PAR interception ( f), canopy extinction coefficient ( k) and radiation-use efficiency (RUE) for wheat, pea and mustard were examined in a field experiment conducted over 5 years in a semi-arid environment in Australia. Two crop sequences were compared: fallow–wheat–pea and mustard–wheat–pea. Significant periods of water stress occurred in some years. Complete ground cover was not achieved and f ranged to maxima of 0.77, 0.80 and 0.80 in wheat, pea and mustard, respectively. For wheat, fallow increased f under both average growing season and drought conditions, but pea PAR interception was not influenced by crop sequence. Estimates of k for wheat, pea and mustard were 0.82 (±0.05), 0.76 (±0.03) and 0.68 (±0.12), respectively. Estimated RUE (aboveground biomass) of 1.81 (±0.05), 1.52 (±0.05) and 1.92 (±0.12) g MJ −1 intercepted PAR for wheat, pea and mustard, respectively, was measured over the vegetative phase. Seasonal conditions had minimal impact on k and RUE, and RUE was generally lower than the maxima reported in the literature, but they were similar to others reported in comparable environments and matched predicted unstressed RUE for C 3 plants. This calls into question the application, in simulation models for crops that rarely reach full cover in such arid environments, of water supply or stress factors to RUE values established elsewhere on unstressed crops.

EFFECTS OF PINE PLANTATIONS ON ULTRAMAFIC VEGETATION OF CENTRAL ITALY

The influence of pine plantations on typical ultramafic plant communities of Tuscany was investigated by means of thirty 5 × 5 m plots in three environmental situations with different pine canopy cover. The main changes in natural vegetation were an increase in species richness and ground cover, resulting from the spread of alien grassland and woody species, and the almost complete disappearance of therophytes and some of the serpentine plants. The typical Armerio-Alyssetum bertolonii, an endemic garigue-steppe association characterized by large areas of bare soil, was modified into a grassland community with almost complete ground cover. The main soil changes associated with the presence of a pine canopy were found to be increases in depth and organic matter. Exchangeable cation concentrations increased with pedological evolution and were positively correlated with organic matter content. The positive relationships between soil metal ion content, species richness, and ground cover suggest that hydrological and nutritional soil characteristics were more determinant for typical ultramafic vegetation than soil metal toxicity. Artificial pinewoods may be a serious threat to biodiversity conservation, because the α-diversity increase found at the spatial scale of the present study would correspond to a β- and γ-diversity decrease should pine plantations spread to all ultramafic areas.

Canopy water deficit detection in paddy rice using a high resolution field spectroradiometer

Reflectance factor spectra in the visible, near, and mid-infrared ranges from canopies of rice plantings that were flooded throughout the crop season (controls) were compared with the treatment drained on a predetermined date, and sheltered from rainfall, to induce water stress. Spectra sampled at 5 nm intervals in the 400–900 nm range and 10 nm intervals in the 900–1900 nm range and their first derivatives were statistically analyzed by ANOVA for two sources of variation, cultivars and water stress, each measurement date. Near infrared (1190–1320 nm) and mid-infrared (1600 nm) band reflectances, and the first derivative at 1230 nm responded promptly to the removal of paddy surface water even for complete ground cover (LAI = 5) during vegetative development. The first derivative at 960 nm, corresponding to a small water absorption band, detected the water status of canopies about 10 days after drainage. Response in the first derivative preceded by a few days the leaf water content deficit, the visual symptoms of wilting and leaf roll, and the decrease in visible red (RED) and near infrared (NIR) reflectances expressed as the normalized difference vegetation index, NDVI = (NIR - RED) (NIR + RED) . Findings indicate that high spectral resolution reflectance measurements and their first derivatives in near and mid-infrared ranges offer a promising method for early detection of water stress in rice canopies.

Agronomic modification of competition between cassava and pigeonpea in intercropping

Cassava ( Manihot esculenta Crantz) and pigeonpea ( Cajanus cajan [L.] Millsp.) are long-season crops and are highly competitive in intercropping. This work was undertaken to examine such competition, using two cassava cultivars of contrasting canopy size and pigeonpea sown at two different times at two plant densities. In all intercropping treatments, radiation interception by the combined canopy increased rapidly, and full ground cover was maintained up to pigeonpea harvest (ca 100 days). However, the proportion of ground area covered by each component species (canopy width) varied greatly among treatments. When pigeonpea was planted simultaneously with cassava, it became taller than cassava and its canopy occupied most of the cassava interrow space. When it was sown 35 days later than cassava, then cassava cultivars MCol 1468, which was tall and had a large canopy, dominated pigeonpea almost completely, whereas the smaller cultivar MAus 19 occupied up to only about half the total interrow area. Pigeonpea at high plant density (based on four rows between cassava rows) had similar height to that at low density (based on two rows), but its canopy occupied more interrow space and enhanced its competitiveness. The canopy width during the time of the complete ground cover was directly related to total dry-matter production and partial land equivalent ratio (LER) for economic yield of each component crop. However, cassava LER was more sensitive to reduced cassava canopy width than was pigeonpea LER, and higher total LER was obtained when a large cassava canopy width was maintained. It is therefore concluded that a vigorous cassava cultivar and late sowing of pigeonpea at a low density can sustain the desirable canopy width and competitiveness for high productivity of cassava/pigeonpea intercropping.

Establishment of Two Bermudagrasses in Three Soil Environments

AbstractTifton 44 hybrid bermudagrass [Cynodon dactylon (L.) Pers.], has been reported to be more cold tolerant and to give better animal gains than the hybrid Coastal. It has been observed that Tifton 44 has not established as rapidly as Coastal, frequently taking 2 to 3 yr to achieve complete ground cover. The objective of this work was to determine and quantify differences in the field establishment of Coastal and Tifton 44 grown at three locations for 2 yr on clayey, kaolinitic, thermic Typic Hapludult (Cecil and Mayodan) and loamy, siliceous, thermic Grossarenic (Blanton) soils in North Carolina. A single row of sprigs was set in the center and the length of each 3.1‐ by 6.2‐m plot. Establishment effects were measured by weekly counts of the number of tillers/stolons intercepting a series of transect lines spaced at 0.15‐m intervals on both sides of the sprigged row, and by harvesting the forage produced at the end of the season in 0.30‐ by 6.1‐m increments from the center to the border of each plot. Two establishment indices were developed as the response variables from the transect count data. Analyses of variance were conducted on yield, establishment indices, and on spring ground cover estimates. Yield of forage and establishment characteristics were similar for Coastal and Tifton 44 on the Mayodan soil, but Coastal established more rapidly and produced more forage than Tifton 44 on the Cecil soil in both years of the trial and on the Blanton soil during the first year. In three of six trials, Tifton 44 would have required a 0.3‐ to 0.6‐m row spacing to equal the coverage obtained by Coastal in a 0.9‐ to 1.2‐m row spacing.

Effect of Temperature on Interception and Conversion of Solar Radiation by Stands of Groundnut

Stands of groundnut were grown in controlled environment glasshouses at air temperatures of 19, 22, 25, 28, and 31 °C. Leaf area index (L) increased with rise of temperature, and after 85 d was about 10-fold larger at 31 °C than 19 °C. Over most of the range of temperature, both L and fractional interception of solar radiation (/) were functions of thermal time accumulated from sowing (above a base of 10 °C). In this respect, they were tightly coupled to developmental rate at the main apex. In one experiment, only 38% of seeds emerged at 22 °C and 21% at 19 °C, compared with more than 70% at 25 °C and 31 °C, but the low population density was compensated by faster leaf expansion by each plant (at 22 °C only) and a greater fraction of solar radiation intercepted by unit leaf area. The amount of solar radiation intercepted by stands increased with rise in temperature, but the greatest differences between treatments occurred before the canopies achieved complete ground cover (i.e./> 0-9) and the relative effect of a rise in temperature diminished the longer the duration of growth. The dry matter produced for unit solar radiation intercepted was not strongly affected by temperature between 22 °C and 31 °C, where the mean was 21 g MJ1; the value at 19 °C was uncertain since the stands were sparse throughout the experiment. After 85 d, the stand at 31 °C had produced eight times the dry matter of that at 19 °C—a difference caused mainly by the effect of temperature on the rates of development and expansion.

The response of an autumn‐sown determinate faba bean to different plant distributions

SUMMARYThe response of an autumn‐sown determinate selection, 858, to different plant distribution patterns was examined in field trials during the two seasons 1985/86 and 1986/87 at the University of Nottingham. Plants were sown at two densities (20 and 40 plants per m2) and at three different row widths (11.9, 23.8 and 47.6 cm) in the autumn of each season.Plant numbers and combined yields were greater in 1986/87 than in 1985/86. Grain yield was unaffected by differences in inter‐row spacing and this was ascribed to the early attainment of complete ground cover even when plants were grown in widely spaced rows. Yield was most strongly correlated with seed numbers per m2.An examination of yield on a per plant basis suggested that narrow inter‐row spacings were more productive at low plant densities, while yield per plant was greater at higher densities if the crop was grown on wider inter‐row spacings. It was concluded that autumn‐sown determinate forms of faba bean were able to compensate for large changes in plant distribution and consequently yield was unaffected.

Herbaceous Legumes as Nutrient Sources and Cover Crops in the Rwandan Highlands

Herbaceous legumes were assessed for their suitability as nutrient sources and as ground cover for the northern highlands of Rwanda. There were three investigations which followed the Farming Systems Research (FSR) methodology. First, exploratory studies were conducted to measure biomass yield and percentage ground cover. Second, 12 legumes were screened on station for biomass production, nutrient yield and ground cover. Yields of maize (Zea mays) grown as a test crop following incorporation of the legumes were compared with yields of maize grown at different nitrogen levels. Third, following farmers' comments on the second study's results, five legume species were chosen for multilocational testing on 11 farmers' fields. Preliminary studies showed high biomass yields and good ground cover for Desmodium sp, Trifolium sp (red clover), Vetch sp, and Stylosanthes sp. Trifolium repens (white clover) demonstrated a prostrate and complete ground cover—ideal characteristics for live-mulch species. On-station experiments indicated significant accumulation of nutrients by the legumes, but with substantial site-species interaction. Legumes with high biomass yields decreased maize yields when compared with maize grown with no nitrogen. The multilocational testing confirmed the inconsistent performance of the species at different sites and led to the definition of three sub-regions (North, Central and South) for which different promising legumes were selected. Selection criteria such as vegetative yield, nutrient content and ground coverage resulted in the following selections by region and in order of preference: North: Canavalia, Lupin, Mucuna; Central: Vetch, Lupin; and South: Mucuna, Lupin and (on fertile soil), Canavalia. In terms of legume growth performance, this study suggests possible benefits from 1) moderate initial fertilization, 2) extended vegetative growth, 3) high sowing densities and 4)sowing in mixtures on infertile soils. Short-term crop yield losses due to net immobilization of soil nutrients by some cover crops (e.g. Vetch) may make legumes unacceptable to small-scale farmers. Research on decomposition and nutrient release is recommended prior to extension of legumes to farmers.