Row Position Research Articles

Using High‐Resolution Soil Moisture Data to Assess Soil Water Dynamics in the Vadose Zone

Infiltration and water flow in soils are highly transient processes, but may be estimated from high frequency measurements of soil water content. The objectives of our study were to assess the impact of vadose zone soil water dynamics from real‐time and near‐continuous soil water content measurements and to assess the interactive effects of tillage, row position, and season on water infiltration, storage, drainage, and crop water uptake. Multisensor capacitance probes were installed at row and interrow positions at four soil depths in plow tillage (PT) and no tillage (NT) corn (Zea mays L.) plots, with volumetric water contents values recorded every 10 min for a 30‐mo period. Three water parameters (cumulative water storage, net water storage, and drainage below 55 cm) were grouped for statistical analysis by rainfall amounts and “seasons” of primary periods of groundwater recharge and evapotranspiration. Crop water uptake amounts during extended dry‐down periods were also quantified. We found more significant differences between tillage and row position treatments for high rainfalls (>17 mm) than for low rainfalls. When significant differences in the three water parameters existed between positions, these were due either to greater values in the row position or smaller values at the traffic interrow position. In general, more water uptake took place under PT than under NT and from row more than interrow or traffic interrow positions. These results show both the value and limitation of near‐continuous real‐time soil water data for quantifying soil water dynamics in varying management and weather conditions.

Distribuição espacial da meleira do mamoeiro em zonas de trópico úmido e trópico semi-árido

O vírus da meleira, transmitido por Bemisia tabaci, é um dos maiores problemas da cultura do mamoeiro (Carica papaya), sendo responsável por perdas de até 100% na produção. Com o objetivo de compreender melhor sua epidemiologia e gerar subsídios para estudos da influência de fatores culturais e bioecológicos na dinâmica da doença, avaliou-se a distribuição espacial de plantas afetadas pela meleira em zonas de Trópico Úmido e Trópico Semi-árido, em 15 plantios comerciais em Eunápolis-BA e Petrolina-PE, entre jan. 2000 e mar. 2001. As áreas foram mapeadas anotando-se a posição de cada planta e a presença ou ausência de sintomas. Foram consideradas doentes aquelas que apresentavam frutos com exsudação espontânea do látex, látex muito fluido, frutos borrados e/ou folhas do ápice com o bordo necrosado. Pelas análises de seqüências ordinárias, índice de dispersão, áreas isópatas e ajuste dos logaritmos das variâncias binomial e de acordo com a lei de Taylor, observaram-se maior agregação nas linhas de plantio que entre linhas e uma agregação de mediana a forte em sub-áreas (1,4 < ID < 3,1). Na maioria dos lotes, as áreas de maior incidência concentraram-se nas bordas dos talhões, o que indica que a migração de vetores assume um papel importante na disseminação da doença. Em alguns casos foi possível detectar a presença de focos isolados no interior dos lotes, o que sugere a formação de colônias dos vetores e transmissão planta a planta a partir de inóculo secundário. Não foram observadas diferenças significativas na distribuição espacial de plantas doentes entre as áreas das duas regiões.

Microenvironment of a corn–soybean–oat strip intercrop system

The microenvironment of a corn ( Zea mays L.)–soybean ( Glycine max [L.] Merr.)–oat ( Avena sativa L.) narrow strip intercrop system was studied on four farms in Iowa, USA during 1991–1993 (one or two farms studied each year) with the objective of explaining previously observed patterns of strip-crop yields. Air and soil temperatures, humidity, wind, and photosynthetic photon flux density (PPFD) for each row in a strip were recorded continuously during 4–13-day periods several times during each growing season; short-term measurements of light extinction through the corn and soybean canopies were made late in the 1993 growing season. Soybean biomass in September 1993 was also determined. Early in the growing season, there typically were no significant differences among rows within a strip in any environmental or growth variable. Later in the growing season, daily PPFD received varied more across each strip than any other environmental variable measured; the outer side of edge rows of corn in north–south rows typically received significantly higher daily PPFD (2–38% more) than inner rows in the strip, while the outside of the soybean row furthest from corn received 36–140% greater PPFD than the corn-side of the row next to the corn strip. Soybean height; leaf mass per leaf area; and leaf mass, stem mass, and pod mass per unit land area in September were strongly related to daily PPFD, with all except height increasing with greater PPFD. Total biomass increased by 32% from the row closest to corn to the row furthest from corn, although there was no change in the ratio of leaf:stem:pod with row position. Thus, PPFD varied the most across the strips of any environmental variable, and crop growth was closely related to PPFD received.

Novel relational database for tissue microarray analysis.

Novel relational database for tissue microarray analysis.

Effects of farmyard manure and tillage systems on soil physical properties and corn yield in central Iran

Tillage management and manure application are among the important factors affecting soil physical properties and crop yield. A 2-year field experiment was conducted on a silty clay loam soil (fine-loamy, mixed, thermic Typic Haplargids). Effects of two tillage systems (moldboard plowing as conventional tillage ( T 1) and disk harrowing as reduced tillage ( T 2)) at three farmyard manure rates (zero ( M 1), 30 ( M 2), 60 ( M 3) Mg ha −1) were studied on the soil physical properties and corn ( Zea mays L.) yield. The experiment was carried out in split block design with three replications. Organic matter (OM) content, bulk density (BD), saturated hydraulic conductivity ( K S), aggregate mean weight diameter (MWD) and dry biomass yield (DBY) were measured after harvesting in the second year. Manure application increased OM on both the row and inter-row tracks significantly. Manure application rate of 60 Mg ha −1 increased MWD (0.33, 0.40 and 0.75 mm for M 1, M 2 and M 3, respectively) at the 0–5 cm soil layer, but the effect was not significant below 5 cm depth. Adding manure significantly decreased soil BD on the row tracks (1.39, 1.22 and 1.17 Mg m −3 for M 1, M 2 and M 3 treatments, respectively), but did not have any significant effect on the inter-row tracks. Hydraulic conductivity was improved by manure applications both on the row and inter-row positions. Manure treatments M 2 and M 3 increased DBY compared to the M 1 treatment. Although moldboard plowing increased the depth of root penetration significantly (43 cm for T 1 and 30 cm for T 2), the effect of tillage systems on yield and soil physical properties was not significant.

Tillage effect on nutrient stratification in narrow- and wide-row cropping systems

Recent research has indicated that conservation systems with narrow-rows have potential for higher crop productivity on southeastern USA Coastal Plains Soil. The objective of this study was to determine how surface tillage and subsoiling affect nutrient distribution in the soil profile in narrow- and wide-row systems. A secondary objective was to determine the effect of row position on soil pH and nutrient concentrations in the wide-row system. Soil samples were collected in 1996 from plots that had been growing soybean ( Glycine max (L.) Merr.) double cropped with wheat ( Tritiucum aestivum L.) for 3 years and then again in 1999 after 3 years of continuous corn ( Zea mays L.). Narrow-row spacing was 19 cm for soybean and 38 cm for corn. Wide-row spacing was 76 cm for both soybean and corn. Wheat was grown in 19 cm wide-rows. Soil samples were randomly collected from throughout the plots in the narrow-row culture. In the wide-row culture, separate samples were collected from the row and from between rows. Treatments were surface tillage (disc tillage (DT) and no surface tillage (NT)), with different frequencies of subsoiling. The soil type was Goldsboro loamy sand (fine-loamy, siliceous, thermic, Aquic Kandiudult). Soil samples from four depths (the surface 5 cm of the A horizon, the remainder of the A horizon, the E horizon, and the top 7.5 cm of the B horizon) were analyzed for pH, P, K, Ca, and Mg. Nutrient concentrations and pH differed little between row spacings at any depth after either 3 or 6 years. Differences due to subsoiling appeared mainly due to nutrient removal as the treatments with more intense subsoiling had higher yield and lower concentrations of nutrients (except K). Concentrations of P, Mg, and Ca at the soil surface tended to be higher in NT than in DT, especially in the mid-rows of the 76 cm wide-row systems. The data suggest only small differences in soil nutrient stratification can be expected as growers adopt narrow-row crop production systems with intensive subsoiling.

Effect of tillage on microbial characteristics and herbicide degradation in a Sharkey clay soil

Field and laboratory studies were conducted at Stoneville, MS, from 1996 to 1998 to determine the influence of subsoiling (SS) and conventional tillage (CT) of a Sharkey clay soil on microbial characteristics and herbicide degradation. Soil samples obtained from imazaquin-treated and nontreated plots from the soybean row and interrow position were analyzed. Because only the row position is actually disturbed by SS, a comparison of row and interrow position on the parameter was conducted. Imazaquin (preemergence, 140 g ai ha−1) had no effect on microbial populations, microbial enzyme activity (fluorescein diacetate [FDA] hydrolysis and triphenyl-tetrazolium chloride [TTC] dehydrogenase), and organic carbon content. Estimates of microbial activity based on FDA hydrolysis and TTC dehydrogenase activity indicated greater activity under CT; however, microbial biomass and organic carbon were not affected by tillage or row position. A laboratory study assessed the degradation of carboxyl- and ring-labeled 2,4-D as influenced by tillage and row position. Soils from CT plots had an initially higher mineralization rate of 14C carboxyl-labeled 2,4-D compared to soils from SS plots; however, no effect of tillage or row position was observed on the cumulative amount of 14CO2 evolved 14 d after treatment (DAT) in 1996 and 18 DAT in 1998. In studies with ring-labeled 2,4-D, a higher 14CO2 evolution was detected in soils obtained from SS plots, regardless of row position, whereas a greater amount of radioactivity was observed in the unextractable fraction from CT soils. Because differences in 2,4-D mineralization between tillage regimes were minimal, adoption of SS as a tillage practice for heavy clay soils in the Mississippi Delta may have a limited effect on microbial characteristics and biodegradation of soil-applied herbicides.

Tillage and Row Position Effects on Water and Solute Infiltration Characteristics

Biological channels and wheel track compaction zones increase heterogeneity of soil properties affecting infiltration, runoff, erosion, and solute movement. We hypothesized that crop, tillage system, and position relative to the plant row would alter the rate and pattern of water infiltration into a Grenada silt loam (fine‐silty, mixed, active, thermic, Oxyaquic Fraglossudalfs). We compared plant row (ROW), nontrafficked (UTK) and trafficked interrow (TRK) positions for cotton (Gossypium hirsutum L.) and grain sorghum [Sorghum bicolor (L.) Moench] grown with chisel plow, disk, or no‐tillage in the fourth year of a cropping system and tillage study. We used ring and tension infiltration measurements 3 to 10 wk after planting to determine infiltration rate and pore‐size distribution. Infiltration patterns and mobile water contents were studied by ponding Brilliant Blue FCF dye [(N‐ethyl‐N{4‐[(4‐{ethyl[(3‐sulfophenyl)methyl]‐amino}phenyl)(2‐sulfophenyl)methylene]‐2,5‐cyclohexadien‐1‐ylidene}‐3‐sulfoben‐zenemethanaminium hydroxide inner salt, disodium salt)](PYLAM products Co., Garden City, NY) and excavation. Neither tillage nor crop affected ponded infiltration rates that averaged 86.5 mm h−1 for the ROW, 18.6 mm h−1 for the UTK, and 2.4 mm h−1 for the TRK position. Sorghum had more pores (0.04 m3 m−3) between 1.0 and 0.2 mm diam. than cotton (0.02 m3 m−3). Deeper and less uniform dye penetration reflected lower mobile water contents under no‐tillage (0.04 m3 m−3) compared to tillage (0.20–0.27 m3 m−3). This research confirmed the importance of continuous macropores in solute movement, but ponded infiltration rates were only weakly correlated with maximum dye depth and did not reflect tillage system differences in dye patterns.

Soil water dynamics in row and interrow positions in soybean (Glycine max L.)

Quantitative knowledge of infiltration processes and the mechanisms that control water movement in soil is necessary to properly manage water and chemical use in agricultural fields. The objective of this study was to compare the soil water content dynamics in row and interrow positions in a soybean crop (Glycine max L.) under conventional (plow) tillage. Two field plots (Beltsville silt loam soil, Fine-loamy mixed mesic Typic Fragiudult) were instrumented with Time Domain Reflectometry (TDR) probes at 0–10 cm, 0–25 cm and 0–40 cm depths. TDR probes were installed in the row and interrow positions. Soil water content was continuously monitored at 1 hour intervals. The distribution of infiltrated water and evapotranspiration showed strong row-interrow patterns. The row positions received significantly more water during precipitation than the interrow positions. Water loss, due to evapotranspiration, was also significantly greater in the row position than in the interrow position. Both plant and soil characteristics appeared to be important factors for infiltration and redistribution. The results of this study suggested that the presence of the crop canopy altered the surface boundary conditions of the soil and, hence, the volume of infiltrating water. Results of this study suggest that in order to model water movement in row crops, the ability to simulate canopy architecture and flow processes in two dimensions is necessary.

Expressive Law and Oppressive Norms

Many important social interactions can be modeled as chicken or hawk dove games. These games can give rise to two stable equilibrium conventions (hawk/dove and dove/hawk). These conventions are desirable insofar as they permit players to avoid costly conflictual encounters (hawk/hawk). What role does law play in establishing these equilibria? McAdams contends that the law can draw attention to a focal point around which play can coordinate, thus speeding progress towards one of the beneficial conventions. The law can also go one step further: it can select one or the other equilibrium by enacting a positive rule for play. Taking off from McAdams's analysis, this comment addresses how expressive law might influence the rise of oppressive norms or conventions. Those are defined as conventions that take hold in games in which players receive different payoffs from hawk/dove combinations depending on whether they occupy the row or column position and in which occupancy of those positions is fairly fixed. Law is less important in fostering the emergence of conventions in those special cases for two reasons: most such games coordinate around focal identity features that are already naturally salient (displacing the law's role in drawing attention to focal points for play), and the lopsided payoff structure of the games spontaneously determines which convention emerges (displacing the law's role in selecting a convention for play). The comment then addresses how law in its expressive capacity might help bring about changes in entrenched oppressive conventions. It begins with the observation that any shift to an alternative stable pure strategy convention in this context must involve table-turning or a reversal of roles within the existing game. The group that gains more by playing hawk under the dominant convention will gain less by playing dove under the alternative convention, and vice versa. But absent manipulation of payoffs through the imposition of external penalties or a change in player preferences, it is difficult to see how a shift to a new convention would occur spontaneously. That is because no rational self-interested player has any incentive to deviate unilaterally from the dominant strategy of play. (Doves who switch to hawk will suffer losses from a hawk/hawk conflict; hawks who switch to dove will also reduce their payoffs). Recent social history nonetheless demonstrates that oppressive conventions do change. The comment suggests that this occurs when doves move unilaterally into the hawk role despite reduced payoffs in the game. Why might doves do that? Drawing on the work of Edna Ullman Margalit and Robert Frank, the comment suggests that doves defy the existing conventions, even at some cost to themselves, out of moralistic indignation and resentment against the unfairness of their disadvantaged position within the status quo. Doves may come to value improving their position relative to other players or they may seek equality for its own sake. The comment argues that conventions will only change if doves commit to playing hawk regardless of personal consequences, and hawks are convinced of that commitment. If former doves can persuade hawks of their determination to switch strategies, hawks will have reason to abandon their former positions in order to avert their own losses. Based on these observations, the comment concludes that norm changes in hawk/dove games will often be marked by moralistic rhetoric and an appeal to impartial standards. Those appeals signal the determination of former losers (doves) to disgard the status quo regardless of adverse consequences, which in turn helps to convince winners to abandon the status quo as well. These moralistic justifications also provide an impartial rationale for what appears to be a partial result: turning the tables on former winners and elevating former losers. The law can buttress such appeals by reinforcing the normative claims that are made by those who spearhead change. Law can also serve to advertise and coordinate former losers' decisions to force a change despite personal sacrifice, thus recruiting additional individuals to the cause.

Colour and shape analysis techniques for weed detection in cereal fields

Information on weed distribution within the field is necessary to implement spatially variable herbicide application. This paper deals with the development of near-ground image capture and processing techniques in order to detect broad-leaved weeds in cereal crops under actual field conditions. The proposed methods use colour information to discriminate between vegetation and background, whilst shape analysis techniques are applied to distinguish between crop and weeds. The determination of crop row position helps to reduce the number of objects to which shape analysis techniques are applied. The performance of algorithms was assessed by comparing the results with a human classification, providing an acceptable success rate. The study has shown that despite the difficulties in accurately determining the number of seedlings (as in visual surveys), it is feasible to use image processing techniques to estimate the relative leaf area of weeds (weed leaf area/total leaf area of crop and weeds) while moving across the field and use these data in a stratified manual weed survey of the field.

Density functional study of guanine and uracil quartets and of guanine quartet/metal ion complexes

The structures and interaction energies of guanine and uracil quartets have been determined by B3LYP hybrid density-functional calculations. The total interaction energy ΔET of the C4h-symmetric guanine quartet consisting of Hoogsteen-type base pairs with two hydrogen bonds between two neighbor bases is −66.07 kcal/mol at the highest level. The uracil quartet with C6 H6O4 interactions between the individual bases has only a small interaction energy of −20.92 kcal mol−1, and the interaction energy of −24.63 kcal/mol for the alternative structure with N3H3O4 hydrogen bonds is only slightly more negative. Cooperative effects contribute between 10 and 25% to all interaction energies. Complexes of metal ions with G-quartets can be classified into different structure types. The one with Ca2+ in the central cavity adopts a C4h-symmetric structure with coplanar bases, whereas the energies of the planar and nonplanar Na+ complexes are almost identical. The small ions Li+, Be2+, Cu+, and Zn2+ prefer a nonplanar S4-symmetric structure. The lack of coplanarity prevents probably a stacking of these base quartets. The central cavity is too small for K+ ions and, therefore, this ion favors in contrast to all other investigated ions a C4-symmetric complex, which is 4.73 kcal/mol more stable than the C4h-symmetric one. The distance 1.665 Å between K+ and the root-mean-square plane of the guanine bases is approximately half of the distance between two stacked G-quartets. The total interaction energy of alkaline earth ion complexes exceeds those with alkali ions. Within both groups of ions the interaction energy decreases with an increasing row position in the periodic table. The B3LYP and BLYP methods lead to similar structures and energies. Both methods are suitable for hydrogen-bonded biological systems. Compared with the before-mentioned methods, the HCTH functional leads to longer hydrogen bonds and different relative energies for two U-quartets. Finally, we calculated also structures and relative energies with the MMFF94 forcefield. Contrary to all DFT methods, MMFF94 predicts bifurcated CHO contacts in the uracil quartet. In the G-quartet, the MMFF94 hydrogen bond distances N2H22N7 are shorter than the DFT distances, whereas the N1H1O6 distances are longer. © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 109–124, 2001

Soil Water Recharge under Uncropped Ridges and Furrows

Nitrate leaching to ground and surface water is an increasing concern in agriculture. Ridge tillage and associated residue management offer potential for modifying the pattern of soil water and solute movement to reduce NO3 leaching from corn (Zea mays L.) production. To test this idea we used time domain reflectometry (TDR) measurements of volumetric soil water content (θ) at 0.5‐h intervals following natural rainfall events to determine the pattern of infiltration and soil water recharge for uncropped row and furrow positions in long‐term ridge‐tillage fields. Soil water content was measured under adjacent rows and three adjoining furrows for 103 d in 1992 on a Clarion loam (fine‐loamy, mixed mesic, Typic Hapludoll) near Boone, IA and 96 d on Monona silt loam (fine‐silty, mixed mesic, Typic Hapludoll) near Treynor, IA. During rainfall, infiltration occurred primarily in furrows, as indicated by greater and more rapid initial increases in θ for furrow than for row positions at the same elevation. Following redistribution and evaporation, row and furrow positions at the same elevation had θ values differing by <0.03 m3 m−3 Changes in profile average θ of rows and furrows between rainfall events were closely correlated (R2 > 0.94). Storage between rainfall events decreased with increasing initial θ and time interval between events (R2 > 0.68), consequently soil water recharge occurred as a series of stepwise increases of θ. These results support the conclusion that water infiltrated in furrows and primarily moved laterally to row positions, minimizing downward water movement under the row. These results explain greater solute movement under furrows than under rows, as found in several short‐term studies.

The influence of row position and selected soil attributes on Acarina and Collembola in no-till and conventional continuous corn on a clay loam soil

Population abundances of both Acarina (mites) and Collembola (springtails) were examined for continuous corn grown under no-till and conventional management practices on a clay loam, an Orthic Humic Gleysol (Typic Haplaquoll) near Ottawa, Ont., Canada (Lat. 45° 22′ N; Long. 75° 43′ W). For each tillage practice, samples for soil faunal extraction and soil attribute characterization were taken periodically during the growing seasons of 1989 (5 samplings) and 1990 (4 samplings). Each time, samples (0–5 cm depth) were taken every 15 cm across a 1.5 m transect spanning three rows of corn that included both a traffic and a non-traffic row in order to assess if population abundances were significantly influenced by soil attributes related to changes in disturbance and compaction due to row position. Row position had a significant effect (analysis of variance based on split–split plot model) on Cryptostigmata in 1989, and in 1990, on Prostigmata, Onychiuridae, and Cryptostigmata. From canonical correlation analysis, for 1989 and 1990, respectively, 71% and 61% of the variation in the biotic data set could be explained by variation in the abiotic data.

Corn Leaf Orientation Effects on Light Interception, Intraspecific Competition, and Grain Yields

Current environmental concerns justify renewed evaluation of crop management strategies that offer promise for maintaining or increasing productivity while reducing environmental impacts. Field studies were conducted using weed-free conditions to determine the effects of corn (Zea mays L.) leaf orientation on light interception, vegetative and reproductive development, and grain yields. DeKalb 689' was handseeded in north-south rows to achieve populations of 22 000 and 33 000 plantslacre. Controlled seed positioning in the soil was used to attain across-row and with-row leaf orientations, while conventional planting provided random leaf orientation. Light interception, intraspecific competition among corn plants, and grain yield were affected by leaf orientation and plant population. At selected row positions 8 wk after planting, light interception for across-row leaf orientation exceeded random and with-row orientations by up to 10 and 25%, respectively, while light interception for the high plant population exceeded the low population by up to 15%. Across-row and random leaf orientations produced 8% greater leaf area than with-row orientation. Greater intraspecific competition was indicated for the high plant population due to lower leaf area, leaf biomass, and stalk biomass per plant than the low population. Grain yields were greater at the high than the low plant population for all leaf orientations. At the high plant population, across-row leaf orientation yielded 10 and 21% more than random and with-row orientations, respectively. Therefore, across-row leaf orientation at the high plant population should provide more rapid canopy closure, enhance crop competition with weeds, and reduce dependence on herbicides while enhancing grain yields.

MACHINE-VISION WEED DENSITY ESTIMATION FOR REAL-TIME, OUTDOOR LIGHTING CONDITIONS

A system to estimate the weed density between two rows of soybeans was developed. An environmentally adaptive segmentation algorithm (EASA) was used to segment the plants from the background of the image. The effect of two image data transformations on the segmentation performance of the EASA was investigated, and the RGB-IV1V2 transformation resulted in significantly higher quality segmentation results based on morphological opening and closing pixel loss over the RGB-rgb transformation. An adaptive scanning algorithm (ASA) was developed and used to automatically detect crop inter-row edges and to estimate the number of weeds in the inter-row area. Two sets of images were acquired under sunny and overcast sky conditions. The ASA-detected crop row edge positions were significantly correlated with the manually detected crop row positions, with the distribution skewed towards positions internal to the row. ASA weed density estimates were highly correlated with manual weed counts for both lighting conditions. However, when a limited range of the data was considered, much lower correlations resulted, revealing a loss of spatial color resolution due to the transmission of the video signal. The mean execution time of the ASA was 0.038 s for 0.91 m (3 ft) long inter-row regions showing that the algorithm met the real-time constraints necessary to be used as a sensing system for a variable-rate herbicide applicator.

Fertilizer and Soil Nitrogen Use by Corn and Border Crops in a Strip Intercropping System

AbstractCorn (Zea mays L.) has greater yield potential when strip‐intercropped than when monocropped, but this potential may be compromised by a failure to understand how N requirements change with row position and the possible N competition of adjacent crops. A four block, completely randomized, split‐plot experiment was conducted on a Haig loam soil (fine, smectitic, mesic Vertic Argiaquolls) in southern Iowa, to determine crop utilization of N fertilizer pointinjected into corn rows. Nitrogen fertilizer uptake was evaluated in (i) corn rows injected with labeled N fertilizer; (ii) corn rows adjacent to the injected rows; and (iii) plants at the edge of the adjacent soybean [Glycine max (L.) Merr.] and oat (Avena sativa L.)‐alfalfa (Medicago saliva L.) strips. Main treatments consisted of three tillage systems: conventional tillage (CT), reduced tillage (RT), and no‐till (NT). Subplot treatments consisted of point injection of l5N‐enriched NH4NO3 (67 kg N ha−1) in‐row at three row positions within the corn strips. Grain and stover yield, Kjeldahl N, and isotope composition of plant materials were determined. Corn yield and labeled‐N recovery differed with tillage to the extent that tillage affected early and total season moisture availability. Labeled‐N recovery in labeled rows did not differ with row position. Labeled‐N recovery in unlabeled rows or crop borders was typically less than 5% of that recovered by labeled rows. Nitrogen is primarily recovered by the row to which it is applied; therefore, row‐by‐row precision applications seem to be an appropriate management tool.

Centrifuge Testing of Large Laterally Loaded Pile Groups in Sands

An apparatus was developed to load large pile groups (3 × 3 to 7 × 3) founded in sand in the centrifuge laterally. The device consists of a hydraulic jack apparatus to install the piles, strain gauge instrumentation, and a data acquisition system. The instrumentation allowed the determination of both bending moments and shear forces at the head of each pile. Lateral load tests of 3 × 3 to 7 × pile groups were conducted in both loose and medium dense sands. Based on the test results, the pile group interaction effects were investigated. It was found that the p-y multiplier concept was valid. Also, the p-y multipliers (p specifically) are found to be independent of soil density and only a function of the pile group geometry. For this study (pile spacing was fixed at 3 diameters), they were found to be only a function of row position. Single pile tests were also completed for comparison purposes.

Evaluación de las características cuantitativas de 25 accesiones de maíz (lea mays L.) de la zona andina

Con el objeto de evaluar morfológicamente 25 accesiones de maíz (Zea mays L.) de la zona andina, consignadas en el Banco de Germoplasma de ICA-CORPOICA, se aplicó una metodología propuesta por el Centro Internacional de Mejoramiento de Maíz y Trigo (CIMMYT ) que emplea 27 descriptores relacionados con la planta, la mazorca y el grano. El maíz se sembró en surcos de 10m de longitud, con uno a cinco surcos por parcela para cada accesión. En cada una de las parcelas se evaluaron 10 plantas en plena competencia para los caracteres varietales en estudio. Los datos se analizaron mediante estadísticas simples: desviación estándar, coeficientes de variación y correlaciones; para clasificar las accesiones se usaron análisis multivariados de variables canónicas y análisis de conglomerados (cluster). Los resultados mostraron que las primeras cinco variables canónicas explicaron el89% de la variación total; las variables con mayor contribución fueron peso de la mazorca, número de granos por 100 gramos, número de granos por hilera, altura de la planta, ancho de la lámina foliar y posición de la mazorca. Del análisis de agrupamientos, realizado mediante graficación en un plano cartesiano con base en las dos primeras variables canónicas, se pudo inferir que existe diversidad genética en las accesiones de maíz evaluadas, lo cual permitió clasificar las mismas en 7 grupos uniformes según las características morfológicas discriminantes y su lugar de origen.

The Gergonne p-pile problem and the dynamics of the function [formula omitted

The Gergonne p-pile problem is concerned with repeatedly dealing (based upon some “fixed scheme” for collecting and redistributing) a deck of np cards into an n by p matrix and attempting to identify the row position of any elected card in the matrix after some fixed number of deals. Many special cases of this problem give rise to “magic tricks”. In Section 1 of this paper, this problem will be precisely defined and the motivation for studying the “dynamical” properties of the function x |→ ⌊ (x + r) p⌋ will be provided. In Section 2, a general formula for the /th iterate of the aforementioned function will be developed and used to determine the position of any card after the /th deal. Also, the cases in which the aforementioned function has a unique fixed point will be identified and a value (based on n and p) will be given for how many times the deck must be dealt to ensure that the selected card has reached the fixed position. Finally, in Section 3, the results of Section 2 will be extended to more “complicated” schemes in which the collecting and redistributing of the deck is based upon the definition of a periodic omega word in which all of the values are between 0 and p − 1 inclusive.