Abstracts

Andrade, F.H., Calviño, P., et al. 2002, 'Yield Responses to Narrow Rows Depend on Increased Radiation Interception', Agronomy Journal, vol. 94, pp. 975-980.

The response of grain yield to narrow rows can be analyzed in terms of the effect on the amount of radiation intercepted by the crops. The objective of this work was to study the effect of row spacing on grain yield and radiation interception (RI) during the critical period for grain set in three crop species. Ten experiments were conducted with maize (Zea mays L.), sunflower (Helianthus annuus L.), or soybean [Glycine max (L.) Merr.] under irrigation or under dryland conditions without severe drought during flowering and grain filling. The treatments consisted of two row distances combined with other factors such as plant density, cultivar, defoliation, etc. Grain yield responses to decrease distance between rows were inversely proportional to RI achieved with the wide-row control treatment during the critical period for grain number determination (r² = 0.62, 0.54, and 0.86 for maize, soybean, and sunflower, respectively). Moreover, when row spacing was reduced, grain yield increases and RI increases during the critical periods for grain set were significantly and directly correlated in the three crop species (r² = 0.71, 0.64, and 0.94 for maize, soybean, and sunflower, respectively). For the conditions of these experiments, grain yield increase in response to narrow rows was related to the improvement in light interception during the critical period for grain set.

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Baez-Gonzalez, A.D., Kiniry, J.R., et al. 2005, 'Large-area Maize Yield Forecasting using Leaf Area Index Based Yield Model', Agronomy Journal, vol. 97, pp. 418-425.

Large-area yield prediction early in the growing season is important in agricultural decision-making. This study derived maize (Zea mays L.) leaf area index (LAI) estimates from spectral data and used these estimates with a simple LAI-based yield model to forecast yield under irrigated conditions in large areas in Sinaloa, Mexico. Leaf area index was derived from satellite data with the use of an equation developed with LAI measurements from farmers’ fields during the 2001–2002 autumn–winter growing season. These measurements were correlated with the normalized difference vegetation index values from 2002 Landsat ETM+ (enhanced thematic mapper) data. The equation was then tested with 2003 Landsat imagery data. A yield model was validated with maximum LAI and yield data measured in farmers’ fields in northern and central Sinaloa during three consecutive autumn–winter growing seasons (1999–2000, 2000–2001, and 2001–2002). The yield model was further validated with 2002–2003 autumn–winter ground LAI (gLAI) and satellite-derived LAI (sLAI) data from 71 farmers’ fields in northern and central Sinaloa. Grain yield was predicted with a mean error of -9.2% with maximum gLAI and -11.2% with sLAI. Results indicate that the yield model using LAI can forecast yield in large areas in Sinaloa in the middle of the growing season with a mean absolute error of -1.2 Mg ha^-1. The use of sLAI in place of ground measurements increased the mean absolute error by 0.3 Mg ha^-1. Nevertheless, the use of sLAI would eliminate aborious LAI measurements for large-area yield prediction in Sinaloa.

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Blaser, B.C., Gibson, L.R., et al. 2006, 'Optimizing Seeding Rates for Winter Cereal Grains and Frost-Seeded Red Clover Intercrops', Agronomy Journal, vol. 98, pp. 1041-1049.

Growing winter cereal grain/forage legume intercrops can provide multiple benefits to cropping systems in the North Central USA. Intercropping red clover (Trifolium pratense L.) with winter cereal grains can provide forage and a green manure crop. Seeding rate recommendations for sole crops may not optimize intercrop system productivity if interactions exist. This study was conducted during the 2002–2003 and 2003–2004 growing seasons to determine optimum cereal grain and red clover forage seeding rates for maximum returns using partial budget analyses. In March, red clover was frost-seeded at 0, 300, 600, 900, 1200, and 1500 seeds m^–2 into winter wheat (Triticum aestivum L.) and triticale (X Triticosecale Wittmack) seeded at 100, 200, 300, and 400 seeds m^–2 the previous October. Triticale and wheat maximized returns at seeding rates of 300 and 400 seeds m^–2. No cereal grain by red clover seeding rate interactions were detected for red clover dry matter production (DM). Red clover plant densities after cereal grain harvest were 10 to 22% of the original seeding rates. Red clover DM production and return was maximized at 3.49 Mg ha^–1 with 900 seeds m^–2 in 2003 and 6.67 Mg ha^–1 with 1200 seeds m^–2 in 2004. Winter cereal/red clover intercrops in the North Central USA can maximize return using a cereal grain seeding rate between 300 and 400 seeds m^–2 and red clover seeding rates between 900 and 1200 seeds m^–2.

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Campbell, G.S., Use of the AccuPAR Ceptometer to Quantify Effects of Riparian Vegetation Removal on Stream Energy Balance Washington, Decagon pp 1-3

When the vegetation along a stream bank is removed, the solar load on the stream increases. This results in increased stream water temperature. Elevated stream temperatures degrade freshwater habitats, shifting species composition, and often endangering some of the species that live in the stream. An increasing awareness of this problem has led to the creation of riparian strips to shade streams when timber is harvested or prescribed burns are undertaken. The challenge is to know how much shade is needed, and how large to make the strips.

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Gibson, L.R., Singer, J.W., et al. 2008, 'Optimum Stand Density of Spring Triticale for Grain Yield and Alfalfa Establishment', Agronomy Journal, vol. 100, no. 4, pp. 911-916.

Triticale (xTriticosecale Wittmack) has potential as a feed crop in the north central United States and could also function as a companion crop for alfalfa (Medicago sativa L.) establishment. The objectives of this research were to assess the suitability of a short-statured spring triticale as a companion crop and determine optimum triticale seeding rates for grain yield and alfalfa establishment. Spring triticale ‘Trimark 37812’ and alfalfa were grown in companion at Ames and Sioux Center, IA during 2004 and 2005. Triticale was seeded at 198, 297, 396, 495, and 594 pure live seeds (PLS) m^–2 and alfalfa was seeded at 600 PLS m^–2. The grain yield response to changes in stand density was quadratic with maximum yield occurring at 516 plants m^–2. A plant density of 325 plants m^–2 and a seeding rate of 374 seeds m^–2 resulted in maximum profit. The grain yield at the stand density for maximum profit was 4.4 Mg ha^–1. Increasing the triticale seeding rate had no effect on alfalfa stand density or dry matter yield. Alfalfa stand densities exceeded the 130 plants m^–2 threshold required for maximum long-term productivity suggesting the short-statured spring triticale cultivar used in this study was well suited for companion cropping with alfalfa.

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Girona, J., Mata, M., et al. 2006, 'The use of Midday Leaf Water Potential for Scheduling Deficit Irrigation in Vineyards', Irrigation Science, vol. 24, pp. 115-127.

Midday leaf water potential (Ψ_md) was monitored for 3 years at a commercial vineyard (cv. Pinot oir) under four irrigation strategies. Three treatments were established based on irrigating vines with 4–6 mm/day, when daily measured Ψ_md was more negative than the predefined threshold. After the first experimental year, thresholds were adjusted for each treatment as: (1) Control (C), irrigated when Ψ_md was less than -0.6 MPa at the beginning of the season and gradually fell to -0.8 MPa at about mid-June, after which the threshold was maintained at -0.8 MPa until harvest. (2) Control–Deficit (CD), irrigated as C from bud-break to mid-June (around the middle of Stage II of fruit growth), and from then until harvest when Ψ_md decreased below -1.2 MPa. (3) Deficit–Deficit (DD), irrigated when Ψ_md was less than -1.0 from bud break to mid-May (about the middle of fruit growth Stage I), and after that time the Ψ_md threshold became -1.2 MPa until harvest. A fourth treatment was applied following a soil water budget approach (WB). All treatments were replicated five times but irrigation in the Ψ_md-based treatments were independently applied to each of the replicate plots, whereas irrigation for WB was applied equally to all replications. The more site-specific information obtained from Ψ_md thresholds in C provided substantial advantages for yield homogeneity and repeatability of results with respect to WB, thus demonstrating the method’s greater ability to account for spatial variability. Average applied water for the 3 years in C, CD, and DD was 374, 250, and 178 mm, respectively, while the yields were 11.8, 9.2, and 6.1 kg/vine, respectively. The CD treatment produced better juice quality than C, and was superior in other quality parameters to both C and DD. However, over the study period, an important carryover effect was observed in the yields and the grape size of CD, which tended to diminish from year to year relative to C.

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Hyer, E. and Goetz, S.J. 2004, 'Comparison and Sensitivity Analysis of Instruments and Radiometric Methods for LAI Estimation: Assessments from a Boreal Forest Site', Agricultural and Forest Meteorology, vol. 122, no. 3-4, pp. 157-174.

Retrievals of LAI from inversion of canopy radiometric measurements, using the Li-Cor LAI-2000 Plant Canopy Analyzer and the Decagon AccuPar Ceptometer (a linear quantum probe) were analyzed and compared. Field data were collected from 34 sites in the boreal forest of interior Alaska, and sensitivity tests were conducted to estimate the effect of a variety of measurement conditions on the LAI retrievals.We also tested the response of estimated LAI to different values of the theoretical parameters in the retrieval algorithms. Uncertainty in the incident radiation level was magnified by the LAI retrieval, meaning that even small errors in this measurement significantly affected the LAI estimates. Changes in solar zenith angle over long data acquisition times also contributed to the errors. The most important quality control factors for accurate retrieval of LAI from field measurements were the incident radiation and solar zenith angle. A series of sensitivity tests showed that extreme values of leaf angle distribution could change LAI estimates, but our multi-angle measurements produced results consistent with a spherical leaf angle distribution. Alternative methods taken from the literature for post-processing of the data from the two instruments produced similar results for the LAI-2000, but widely different results for the Decagon AccuPar. Retrievals from the two instruments had an overall correlation coefficient r = 0.88, (P < 0.01). Agreement was considerably better in aspen stands (r = 0.85, P < 0.01, N = 43) than in spruce (r = 0.56, P < 0.05, N = 22). Some of the variability was attributed to spatial heterogeneity within stands, particularly sparse spruce canopies. Overall, our results suggest the retrievals were robust, and largely comparable between instruments over a range of measurement conditions, provided variability in measurement conditions was adequately characterized.

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Lopez, G., Mata, M., et al. 2006, 'Mitigation of Effects of Extreme Drought During Stage III of Peach Fruit Development by Summer Pruning and Fruit Thinning', Tree Physiology, vol. 26, no. 4, pp. 469-477.

A water deficit during stage III of fruit growth was established with the aim of determining if it is possible to achieve an improvement in tree water status by summer pruning and fruit thinning. The experiment was set up as a randomized block split-plot design across trials (irrigation) where pruning was assigned to the main plot and fruit thinning to the sub-plots. The irrigation treatments were (1) standard full irrigation (FI), and (2) suppression of irrigation during stage III of fruit growth until leaves visibly withered (LWI); the pruning treatments were (1) experimental summer pruning (EP), and (2) standard summer pruning (CP); and three fruit thinning intensities were applied to facilitate analysis of the effects of the treatments in relation to fruit load. Changes in amount of light intercepted and in tree stem water potential (Ψ_stem) were evaluated. The EP treatment reduced the amount of light intercepted by the tree. In the FI treatment, there was a significant reduction in fruit growth measured as both water accumulation and dry mass accumulation. Under FI conditions, reductions in fruit load as a result of EP were not accompanied by a significant improvement in Ψ_stem. In the LWI treatment, EP produced a significant improvement of 0.17 MPa in Ψ_stem, but there was no improvement in fruit growth compared with CP trees. A reduction in fruit load from 350 (commercial load) to 150 per tree significantly improved Ψ_stem by 0.3 MPa at the end of stage III of fruit growth. These results indicate that improvements in water status in response to pruning may be insufficient to promote fruit growth if the pruned trees are unable to provide an adequate supply of assimilates to the developing fruits.

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Maddonni, G.A., Cirilo, A.G., et al. 2006, 'Row Width and Maize Grain Yield', Agronomy Journal, vol. 98, pp. 1532-1543.

Maize (Zea mays L.) grain yield increase in narrow rows (0.35–0.50 m) may be related to the improvement of light interception around silking, but percentages of grain yield increase are generally lower than those of light interception, suggesting a lower efficiency to convert the amount of intercepted photosynthetic active radiation (IPAR) into aboveground phytomass. We analyzed the effects of plant population and row spacing on grain yield and its components (kernel number and kernel weight) and on the underlying processes, the IPAR around silking and during the effective grain filling period, and radiation use efficiency (RUE) during both periods. Field experiments were conducted in Argentina from 1997 to 2001. Five hybrids were cultivated at a wide range of plant population densities (3, 4.5, 9, and 12 plants m^–2) and row spacings (0.35, 0.50, 0.70, and 1 m) without water and nutrient limitations. Row spacing reduction increased IPAR around silking at low plant densities (~8 and 4% for 3–4.5 and 9–12 plants m^–2, respectively) but did not modify RUE during this period. Morphogenetic limitations in the reproductive organs of plants (number of florets per ear) cultivated at low stand densities, suppressed the slight benefits of enhanced light capture under narrow rows, yielding similar kernel numbers at any row spacing. Contrarily, a postsilking RUE reduction (~13–16%) of crops in narrow rows compared to those in wide rows minimized or counterbalanced any positive effect on IPAR during the grain-filling period. Hence, for the tested growing conditions, no benefits could be expected in terms of grain yield by reducing row spacing from the present 0.7- to 0.8-m inter-row distance.

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Nyakatawa, E.Z., Reddy, K.C., et al. 2000, 'Tillage, Cover Cropping, and Poultry Litter Effects on Cotton: II. Growth and Yield Parameters', Agronomy Journal, vol. 92, pp. 1000-1007.

The development of conservation tillage systems for cotton (Gossypium hirsutum L.), capable of reducing soil erosion and improving soil quality while increasing yields and profits, remains a challenge in the southeastern USA. Poor emergence and growth, delayed maturity, and reduced yield are some of the problems that have been encountered in the use of conservation tillage on cotton. The objectives of this study was to evaluate the effects of tillage (no-till, mulch-till, conventional till), cropping system [cotton–winter fallow, cotton–winter rye (Secale cereale L.) cover crop] and N source (poultry litter, ammonium nitrate) on growth and yield of cotton from 1996 to 1998 in northern Alabama. In 1997, cotton lint yield under no-till (NT) was 24 and 18% greater than that under conventional till (CT) and mulch-till (MT) systems, respectively. In 1998, cotton lint yield under the NT system was 7% greater than that under CT. Poultry litter (PL) at 100 kg N ha^-1 gave similar lint yield to ammonium nitrate (AN), whereas at 200 kg N ha^-1, lint yields were significantly greater. No-till, cotton–winter rye cropping, and surface application of 200 kg N ha^-1 in form of PL conserved soil moisture in the top 7 cm of the soil. This resulted in early seedling emergence, high seedling vigor, good plant growth, and high lint yield of cotton. These treatments would be appropriate for use in the southeastern USA where soil erosion is a problem and plenty of PL is available each year from the poultry industry.

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Scanlon, B.R., Reedy, R.C., et al. 2005, 'Evaluation of Evapotranspirative Covers for Waste Containment in Arid and Semiarid Regions in the Southwestern USA', Vadose Zone Journal, vol. 4, pp. 55-71.

Performance evaluation of evapotranspirative (ET) covers is critical for waste containment. The purpose of this study was to evaluate ET covers at sites in Texas and New Mexico representative of arid and semiarid regions in the southwestern USA using water balance monitoring during 4- and 5-yr periods and water balance simulations using short-term (1–5 yr) and long-term (25 yr) climate forcing. Estimated drainage at the Texas site was related to irrigation while measured drainage at the New Mexico site was restricted to the first 2 yr of the 5-yr monitoring period. Evapotranspirative covers work extremely well in these regions because of the dominance of summer precipitation (62–80%) that corresponds to periods of highest ET. Strong relationships between decreases in soil water storage and vegetation productivity at both sites underscore the importance of vegetation in controlling the water balance in these systems. Simulations of the Texas site indicate that drainage can occur in response to high precipitation near the end of the growing season, but such drainage can be eliminated with a capillary barrier. Inclusion of a capillary barrier increased available water storage by a factor of about 2.5 at both sites. The capillary barrier effect of drainage lysimeters can result in underestimation of drainage and overestimation of water storage relative to covers not underlain by capillary barriers. The data from this study indicate that a 1-m-thick ET cover underlain by a capillary barrier should be adequate to minimize drainage to ≤1 mm yr^–1 in these arid and semiarid regions. Comprehensive monitoring integrated with modeling is required to assess total system performance to develop a predictive understanding of ET covers.

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Stancioiu, P.T. and O'Hara, K.L. 2005, 'Regeneration Growth in Different Light Environments of Mixed Species, Multiaged, Mountainous Forests of Romania', European Journal of Forest Research, vol. 125, no. 2, pp. 151-162.

Growth of regenerating trees in different light environments was studied for the mountainous, mixed-species forests in the Carpathian Mountains of Romania. The primary species in these mixtures were silver fir (Abies alba Mill.), European beech (Fagus sylvatica L.) and Norway spruce (Picea albies (L.) Karst). Seedlings/saplings of these species were selected and measured in different stands from two different geographical locations. Regenerating trees were measured for height and diameter growth during the summer of 2002. For each seedling/sapling, percentage of above canopy light (PACL) and stand basal area (BA) were used to access available and occupied growing space respectively. Regeneration growth was compared against these two variables and regression relationships were developed. Using these models, we predicted the dynamics of regeneration as both growth and species composition. Our results showed that in low-light environments (PACL < 20-35%; BA > 30 m²/ha), shade tolerant fir and beech clearly outcompeted the spruce. Therefore, in dense stands, spruce could be eliminated by the shade tolerant species. For intermediate levels of cover (PACL = 35-75%; BA = 15-35 m²/ha) the spruce grew at comparable rates as the beech and fir. All three species showed similar growth rates in open conditions (PACL > 80-90%; BA < 15-20 m²/ha) with the spruce having the tendency to outgrow the others. However, in terms of establishment, such conditions favour spruce and inhibit fir and beech.

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Tewolde, H., Sistani, K.R., et al. 2005, 'Estimating Cotton Leaf Area Index Nondestructively with a Light Sensor', Agronomy Journal, vol. 97, pp. 1158-1163.

AccuPAR, which is a relatively new instrument for estimating leaf area index (LAI) by measuring light interception, has wide distribution but only limited indepenent evaluation of its accuracy. The objective of this study was to evaluate the accuracy of AccuPAR for estimating LAI of cotton (Gossypium hirsutum L.) planted on different row spacings. Cotton LAI was measured nondestructively with AccuPAR and destructively by taking plant samples three to four times during each growing season in 2002 and 2003 on research conducted at three locations in Mississippi, USA. The results suggested that meter accuracy was affected by differences between row spacing and the length of the light-sensing segment of the meter. Supplemental tests showed that meter accuracy improved with meter placement, which eliminated length differences and with near solar noon measurements, which minimized row-to-row shading overlap. We conclude that the meter can more accurately estimate row crop LAI when the under-canopy placement of the meter and the time of measurement are selected so that the light-sensing segment of the meter captures shading of an entire row cross-section and that row-to-row shading overlap is eliminated or minimized.

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