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The response of upland cotton (Gossypium hirsutum L.) to legume and small grain cover crop establishment, in-season nitrogen (N) rate, and fertilizer N placement was investigated in two experiments located in coastal plain Virginia and North Carolina. The first experiment examined 1) soil compaction and cotton yield response to strip-tillage compared to no-tillage with a precision planted tillage radish and 2) the influence of legume mix, rye, and legume mix/rye combination cover crops with four in-season nitrogen (N) rates applied to cotton on cover crop biomass, cover crop nutrient uptake, soil compaction, soil N cycling, petiole nitrate-N (NO3-N) during the first week of bloom, cotton lint yield, and fiber quality parameters over two years. Legume mix cover crops resulted in greater N uptake, soil NO3-N during the growing season, and lint yields compared to LMR, rye, and fallow treatments over both study years. Soil compaction and lint yields were not significantly different between strip-tilled and no-till with tillage radish treatments in either year. Relative lint yields after LM were maximized at 93% relative yield with 110 kg N ha-1 applied in-season while relative lint yields for cotton following LM with 0 kg N ha-1 applied reached 75%, measuring at least 9% higher than cotton following other cover crop treatments. The second experiment investigated the effect of five N rates (0, 45, 90, 135, and 180 kg N ha-1) and three placement methods (broadcast, surface banded, and injected) on lint yield, petiole nitrate-N (NO3-N), lint percent turnout, and fiber quality parameters. Nitrogen rate and placement had a significant effect on lint yield but only N rate affected petiole NO3-N concentration. It was estimated that injecting fertilizer N requires an N rate of 133 kg N ha-1 to achieve 95% relative yield while surface banded fertilizer N required a rate of 128 kg N ha-1 to produce 90% relative yield. A critical petiole NO3-N concentration threshold of 5,600 mg NO3-N kg-1 was calculated to reach 92% relative yield. Other agronomic management practices such as cover crop termination timing, cover crop species blends, and number of fertilizer N applications are of interest in order to develop better recommendations and promote conservation agricultural practices in coastal plain Virginia and North Carolina. / Master of Science / Upland cotton (Gossypium hirsutum L.) response to diverse species cover crop mixes, conservation tillage method, fertilizer N rate, and fertilizer N placement at side-dress was measured in two field studies conducted on the coastal plain soil in Virginia and North Carolina from 2016-2018. The objectives of the following research were to 1) examine the influence of two conservation tillage practices and four cover crop mixes on cover crop biomass production, soil compaction, cover crop nutrient uptake, soil N cycling, petiole nitrate (NO3-N) and cotton lint yield and 2) measure cotton performance in response to five N rate and three placement application methods. Legume mix (LM) cover crops contained more N in biomass, resulting in higher soil NO3-N during the growing season and higher lint yields at harvest compared to a legume mix and rye combination (LMR), rye, and fallow treatments. Soil compaction and lint yield were not significantly different between strip-tilled and no-till/tillage radish treatments in either year. Nitrogen rate and placement had a significant effect on lint yield but only N rate affected petiole NO3-N concentration. Injection of fertilizer N required an N rate of 133 kg N ha1 to achieve 95% relative yield while surface banded fertilizer N required a rate of 128 kg N ha-1 to produce 90% relative yield. A critical petiole NO3-N concentration threshold of 5,600 mg NO3-N kg-1 was also calculated to reach 92% relative yield. Future application of these results can include investigation of optimal N source for Virginia cotton production, best N placement method for cotton grown in high residue systems, and an economic analysis to determine optimum agronomic management for Virginia coastal plain cotton production.

Flue-cured tobacco (Nicotiana tabacum L.) is an intensively cultivated crop that typically receives four to eight primary tillage passes before being transplanted on a raised row-ridge. Strip-tillage, a conservation tillage system that only requires tilling a small strip before transplanting, has been shown to be effective for tobacco producers in southside Virginia. The cost of fertilizer in recent years and the loss of applied nutrients has brought new attention to the impact of cover crops used in conservation tillage on the nitrogen fertilization of tobacco. A two-year study conducted at the Southern Piedmont Agricultural Research and Extension Center evaluated a strip-tillage production system on agronomic performance of flue-cured tobacco and evaluated the impact of cover crop management on soil nitrogen cycling and nitrogen uptake by plants. Treatments evaluated whether a wheat cover crop was broadcast or strip killed, topdressing a wheat cover crop with 0, 22, or 45 kg ha-1, and tobacco fertilization rates. Additional treatments included a soybean residue treatment, and a conventional tillage control. Topdressing wheat with nitrogen resulted in nitrogen being released late in the growing season. Whether a wheat cover crop was strip or broadcast killed had no effect on yield or cured leaf quality. Soybean residue did not provide adequate soil cover, but was shown to be a suitable ground cover option for tobacco production. Wheat not topdressed with nitrogen and tobacco receiving normal fertilization had adequate soil surface residue cover, good cured leaf quality, and yields that were comparable to those of conventional tillage. / Master of Science

The effect of tillage practices on leaching and persistence of atrazine and metolachlor was evaluated in a field study in the Coastal Plain region of Virginia. Field data were also used to validate pesticide transport models, GLEAMS and PRZM. The study was conducted on two 18x27 m plots located in a field that was in the second year of a two-year no-till wheat-beaDs-com rotation. One plot was conventionally tilled using a moldboard plow and a disk harrow before planting of com and application of chemicals. Soil samples were collected on six sampling dates during the crop growing season at 20 randomly selected locations in each plot with the 0-150 cm sampling depth divided into eight increments. Bromide concentrations were analyzed to provide an estimate of solute movement. High rainfall following chemical application led to rapid leaching of bromide, with the chemical moving faster in the no-till profile. Pesticide concentrations also showed a greater potential for leaching in the no-till plot in the early stages of the study. Chemical concentrations were higher in the no-till profile initially, and were higher in the tilled profile toward the end of the season. Atrazine dissipation was higher in the no-till plot, but there was no marked difference in metolachlor dissipation between the two tillage treatments. Over 35% of atrazine mass remained in the soil profile in both plots at the end of the crop growing season. Pesticide concentrations were found to vary largely over the two plots. The field data were used to evaluate the ability of the pesticide transport models, GLEAMS and PRZM, to represent chemical concentration distribution, depth of solute center of mass, and pesticide mass in the no-till and the conventionally-tilled root zone. The models were evaluated in three sequential steps. The fast simulation was completely uncalibrated, using best available estimates for the input parameters. For the second simulation hydrology parameters were calibrated to minimize errors in the hydrology component so as to better evaluate the prediction of pesticide behavior in soil. The third stage of the evaluation used pesticide dissipation half-life calculated from the field data. Model performance was evaluated using both objective and subjective criteria. GLEAMS and PRZM predicted pesticide concentration in soils reasonably well when run without any calibration. Bromide concentrations were predicted closer to the observed values than pesticides. Overall predictions by both models were better in the conventional tillage plot than in the no-till plot. The comparative effect of tillage on observed chemical concentrations was represented better by GLEAMS than by PRZM. The models under-predicted leaching of pesticides in the early sampling dates. Predicted pesticide mass in the root zone were reasonably close to the field measured values. Calibration of the hydrology component of the models did not improve the prediction of pesticide behavior in soils. The use of field pesticide half-life resulted in better prediction of pesticide persistence but did not improve the overall prediction of pesticide behavior in the two plots. The study identifies selection of input parameters and correct interpretation of results as important factors in the effective use of GLEAMS and PRZM as management tools. / Master of Science

The objectives of this research were: 1) to quantify the amount of supplemental nitrogen (N) to maximize organic broccoli (Brassica olearcea var. italica) on transition soils, 2) to evaluate the ability of leguminous cover crops lablab (Dolichos lablab L.), soybean (Glycine max L.), sunn hemp (Crotalria juncea L.) and a sunn hemp and cowpea mixture (Vigna sinensis Endl.) to supply N and suppress weeds and, 3) to compare the effect on N availability and broccoli yield potential of incorporating cover crops with conventional tillage (CT) or mulching cover crops with no-tillage (NT) practices. Broccoli was grown during the third year of organic transition in the spring and fall of 2006 at the Kentland Agricultural Research Farm in Blacksburg, VA. Supplemental N significantly increased broccoli yield up until 112 kg ha-1 with a quadratic correlation with leaf N. The NT treatment yielded no difference during the spring, but in the fall CT surpassed NT. On the other hand, N uptake, measured by leaf N, under NT conditions increased with supplemental N, which suggests NT has equivalent yield potential as CT when N is not limiting. Yields from leguminous residues did not differ, even though quality and quantity of cover crop biomass did. This suggests that N availability from cover crop legumes may be impacted other ecological process such as soil microbial activity. Also, cover crop residues differed in their ability to suppress weeds. The results from this study give organic growers in transition tools to maximize productivity and sustainability. / Master of Science

Field experiments were conducted in 1984 and 1985 in Fluvanna and Montgomery Counties in Virginia, to evaluate HOE-O661 (glufosinate) [ammonium-(3-amino-3-carboxypropyl )-methyl phosphinate], cyanazine (2-[[4-chloro-6-(ethylamino )-s-triazin-2-yl]amino]-2-methyl propionitrile)), glyphosate [N-(phosphonomethyl)glycine] and paraquat (1,1'-dimethyl 4,4'-bipyridinium ion) for the control of vegetation existing at the time of no-till corn establishment. These herbicides were applied alone or in combination with 2,4-D [(2,4-dichlorophenoxy)acetic acid] or dicamba (3,6-dichloro-2-methoxybenzoic acid) at three timings of application. Both locations were heavily infested with annual, biennial, and perennial broadleaf weeds, including horseweed (Conyza canadensis), buckhorn plantain (Plantago lanceolata), field bindweed (Convolvulus arvensis), curly dock (Rumex crispus) and wild mustard (Sinapis arvensis). All four non-selective herbicides provided good overall weed control. The addition of 2,4-D or dicamba generally improved the control of broadleaf weeds in all four experiments. Control of horseweed with paraquat was variable, but improved significantly when dicamba was applied in combination with paraquat. Glyphosate, cyanazine and HOE-O661 alone or in combination with 2,4-D or dicamba provided excellent horseweed control. Wild mustard control with glyphosate was dependent on the weed size and growth stage of development. Control with paraquat, cyanazine and HOE-0661 was not affected by differences in wild mustard size or growth stage. Glyphosate and HOE-0661 provided acceptable field bindweed control alone, and all herbicides gave excellent field bindweed control when applied in combination with 2,4-D or dicamba. Cyanazine and HOE-0661 showed better control of shoot growth on the more difficult-to-control weeds than paraquat and glyphosate when applied alone. With the addition of either 2,4-D or dicamba, cyanazine and HOE-0661 provided better overall weed control, in most cases, than corresponding paraquat and glyphosate combinations. Timing of application and weed size did not significantly affect herbicide activity, even at later application timings when weeds were well established and exceeded 60 cm in height. / M.S.

In full-season-soybean weed management experiments, the addition of glyphosate [N-(phosphonomethyl)glycine], paraquat (1,1'-dimethyl-4,4'-bipyridinium ion), or HOE-0661 [ammonium (3-amino-3-carboxypropyl)methylphosphinate] to chlorimuron [2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino] carbonyl]amino]sulfonyl] benzoic acid] plus linuron [N'- (3,4-dichlorophenyl)-N-methoxy-N-methyl urea] was required for effective weed control, especially of eastern black nightshade (Solanum ptycanthum Dun.). In double-crop experiments over 4 years including 10 experimental sites and 8 different weeds, chlorimuron plus linuron provided good control of vegetation at planting and residual weed control without glyphosate, paraquat, or HOE-0661. Cyanazine [2-[[4-chloro-6-(ethylamino)-1,3,5-triazin- 2-yl]amino]-2-methylpropanenitrile] and 2,4-D [(2,4- dichlorophenoxy)acetic acid] were the most effective herbicides for horseweed (Conyza canadensis (L.)Cronq.) control prior to establishing full-season no-till soybeans (Glycine max (L.)Merr.). In greenhouse experiments, emergence of tobacco (Nicotiana tabacum L.) seedlings was severely inhibited by all chlorimuron-containing treatments and by the highest rates of imazaquin [2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid]. Growth of tobacco transplanted into a treated potting mixture was severely reduced by all rates of chlorimuron-containing herbicides, and to a lesser extent by imazaquin. Postemergence applications of chlorimuron alone or imazaquin did not significantly affect tobacco growth. In the greenhouse, 'Vance' and 'Forrest' soybean varieties were more sensitive to chlorimuron than were 'W-20' (a sulfonylurea-resistant variety), 'Essex', or 'Hutcheson'. Herbicide injury increased with increasing soil pH. Under simulated rainfall conditions, chlorimuron movement in soil increased with increasing pH and rainfall. Soybean injury may be more directly related to chlorimuron in the soil water solution than to the amount of chlorimuron present in the soil profile. Laboratory experiments indicated that tolerance of pitted (Ipomoea lacunosa L.) and entire leaf (Ipomoea hederacea var. integriuscula Gray) morningglories to chlorimuron may be due to reduced herbicide uptake. Sensitivity of 'Vance' soybeans may be associated with the inability to rapidly metabolize chlorimuron herbicide. / Ph. D.

Experiments to evaluate the effects of tillage systems and nitrogen fertilizer rates on fresh market 'Pik Red' tomato (Lycopersicon esculentum Mill.) production were carried out at Blacksburg, Virginia (1981 and 1982) and at Carrasco and Jackson, Uruguay (1981-2). Two tillage systems were used: (a) conventional tillage (CT) - plowed, disced and rototilled, and (b) no-tillage (NT) using paraquat at 0.5 kg/ha. Four different nitrogen (N) rates were used: 40, 80 and 120 kg N/ha broadcast at transplanting and a 40/40 kg N/ha split applications - 40 kg N at transplanting and another 40 kg N after the flowers of the first cluster had set. During 1982, at Blacksburg a 0 kg N/ha rate was added. For all locations and years, water availability was equal or higher in NT plots than with CT after transplanting. The largest differences were found at the beginning of the growing season. Soil under NT tended to be cooler than under CT; these differences in soil temperature are attributed to higher moisture content with NT than CT and the shading effect of the mulch in the NT plots. Soil Nitrate (NO3) content was equal or lower with NT than with CT at Carrasco and Jackson. Absorption of NO3 by the rye cover crop in NT plots probably was a major cause of NO3 differences between tillage systems. Nitrogen, P and K content in leaf tissue were equal or higher while Ca and Mg were equal or lower in NT plants than in CT plants. Nitrogen tissue content was increased by the N rate only at Carrasco; no effect of N rate was found on absorption of other nutrients at Carrasco or Jackson. Total yield was not affected by the tillage systems except for Blacksburg in 1982 when the NT plots outyielded CT plots. Marketable yield was consistently increased by the NT system at all locations and years. Unmarketable yield was equal or higher with CT than with NT. No effect of the N rate was found for any yield or yield components except for Blacksburg in 1981 where the total average weight was affected by the N rate. Water availability rather than N supply is believed to be the limiting factor to yield production at all locations and years. Blossom-end rot was consistently reduced by the NT system at all locations and years. Improved water availability with NT than with CT was probably responsible for a more steady Ca supply to growing fruit with NT than with CT, thus reducing the incidence of the disorder. / Ph. D.

A permeabilidade ao ar (Ka) pode ser utilizada para avaliar alterações que ocorrem na estrutura do solo em virtude de diferentes sistemas de manejo. Este estudo testou a hipótese de que o menor revolvimento do solo sob sistema plantio direto resulta na formação de poros contínuos e melhor condição de aeração no solo. O objetivo do estudo foi avaliar, por meio da Ka, porosidade de aeração (a) e índices de continuidade de poros (K1 e N), a aeração em um Latossolo Vermelho submetido ao preparo do solo convencional (PC) e plantio direto (PD). Amostras de solo indeformadas foram coletadas em cada sistema nas profundidades de 0-0,10 e 0,10-0,20 m em área experimental do Instituto Agronômico do Paraná IAPAR, no município de Ponta Grossa, Paraná. A Ka foi medida pelo método da carga decrescente em seis potenciais mátricos, -2, -6, -10, -30, -70 e -100 kPa. A macroporosidade e a Ka foi maior no PC nas duas camadas avaliadas. A continuidade de poros avaliada pela razão entre Ka e a (K1) foi similar entre os sistemas na camada superficial e foi maior para o PC em subsuperfície. O índice de continuidade N, referente ao coeficiente angular da relação log-log entre Ka e a foi diferente quando determinado para cada amostra individualmente (n=6) e quando obtido com todas as observações (n=120). Os dois métodos revelaram poros mais contínuos no PC em superfície. Na camada de 0,10-0,20 m o primeiro (n=6) não indicou diferença de continuidade de poros entre os sistemas, enquanto o segundo (n=120) resultou em uma maior continuidade de poros nesta profundidade no PD. / Air permeability (Ka) can be used for assessing soil structure changes due tillage systems. This study tested the hypothesis that the less soil disturbance under no-tillage result in continuous pores and better soil aeration conditions. The objective of this study was to evaluate a Rhodic Hapludox aeration dynamics, by measuring Ka, air-filled porosity (ea) and pore continuity indices (K1 and N), under conventional tillage (CT) and no-tillage (NT). Undisturbed soil cores were collected in each systems at depths of 0-0,10 and 0,10-0,20 m in Parana Agronomic Institute research farm - IAPAR, in Ponta Grossa, Paraná. Ka was determined using falling pressure method in six soil water potentials, -2, -6, -10, -30, -70 e -100 kPa. The soil macroporosity and Ka was higher in CT in both depths. The pore continuity assessment by ratio between Ka and ea (K1) was similar between the systems in the top layer and was higher at CT at depth of 0,10-0,20 m. The continuity index N, relative to the slope from the log-log relationship between Ka and ea was different when calculated for each core individually (n=6) or obtained including all data for each tillage (n=120). The two methods revealed a more continuous pores in CT in the top layer. At depth of 0,10-0,20 m the first (n=6) did not indicate pore continuity difference between the systems, while the second resulted in better pore continuity in NT at this depth.

O método de plantio manual de mudas de árvores é predominante no Brasil. Para a redução dos custos com mão-de-obra, aumento de produtividade e qualidade operacional, o plantio manual deve ser substituído total ou parcialmente por operações mecanizadas. Com esse enfoque foram avaliadas as atividades de plantios manual e mecanizado de eucaliptos, bem como de preparo mecanizado do solo, em área pertencente a uma empresa florestal. O plantio manual foi feito por onze trabalhadores rurais, com o uso da transplantadora de acionamento manual. O plantio mecanizado foi realizado por uma máquina de transplantio de mudas, operada por um trabalhador rural e tracionada por um trator. Na área do estudo foram locadas duas parcelas amostrais, formando uma malha de setenta e cinco pontos amostrais para cada sistema de plantio. Os itens do preparo do solo avaliados foram a profundidade do sulco, o diâmetro dos torrões e o volume cilíndrico dos galhos de madeira sobre a faixa de sulcamento. O itens dos sistemas de plantio avaliados foram a presença de defeitos da operação, a distância entre plantas, a altura da parte aérea das mudas e a sobrevivência das plantas após um mês de idade. As ferramentas da qualidade total utilizadas foram os histogramas, o diagrama de causa e efeito, os gráficos de Pareto e de controle. As análises estatísticas dos resultados foram feitas pelo teste t e pelo teste de qui-quadrado Para avaliar o desempenho operacional do sistema manual estimou-se somente a capacidade de campo operacional. No sistema mecanizado foram estimadas as capacidades de campo efetiva e operacional. Nos dois sistemas de plantio foram estimados também os custos horários e operacionais das máquinas e da mão-de-obra. Entre os sistemas de plantio, a distância entre plantas foi diferente estatisticamente, com melhor distribuição das mudas no sistema manual. O número de defeitos por muda plantada foi semelhante estatisticamente entre os sistemas de plantio. Os principais defeitos do sistema manual foram as mudas plantadas com colo encoberto pelo solo e as mudas plantadas fora do centro do sulco, os quais representaram 72,8% do total. No sistema mecanizado, esses defeitos, somados às mudas não plantadas e mudas não firmes, representaram 76,7% do total. A altura da parte aérea foi diferente estatisticamente, tanto no plantio como um mês após. A sobrevivência das mudas efetivamente plantadas, após um mês de idade, foi semelhante estatisticamente. Concluiu-se, assim, que a qualidade em ambos os sistemas de plantio não variaram dentro de padrões aceitáveis pela empresa florestal. O tempo produtivo do sistema de plantio mecanizado foi igual a 48,2%, gerando uma capacidade de campo operacional 60,0% menor do que no sistema manual. Inferiu-se que o número médio de mudas plantadas por trabalhador por hora foi igual a 95 no sistema manual, enquanto que no sistema mecanizado foi igual a 205. O custo operacional estimado do sistema mecanizado foi 44,9% maior do que no sistema manual, fato devido a baixa capacidade de campo operacional observada no sistema mecanizado. / Hand planting of tree seedlings is the predominant method in Brazil. In order to reduce labor costs, increase productivity, and improve operational quality, hand planting should be totally or partially replaced by machine operations. Having this in mind, eucalyptus’ hand and machine planting activities were assessed, as well as those of mechanical tillage, in an area belonging to a forestation company. Hand planting had been carried out by 11 rural workers by using a planting tube. Machine planting had been carried out by using a seedling transplant machine, which was operated by a rural worker and pulled by a tractor. In the study area, two sampling parts were allocated, forming a web with 75 sampling points for each planting system. Tillage items that were assessed included furrow depth, stone diameter, and the cylindrical volume of wood branches on the furrow belt. Planting system items that were assessed included the presence of operation defects, distance between plants, height of the top portion of the seedlings, and plant survival after one month of age. Total quality tools included histograms, cause and effect diagram, control graphs, and Pareto's graphs. Statistical analyses of the results were performed by using test and qui-square test. To evaluate hand planting system’s operational performance, only the operational field capacity was estimated. As for the machine system, effective and operational field capacities were estimated. Labor and machine hourly costs, as well as the operational costs for both planting systems were assessed. When comparing planting systems, the distance between plants was statistically different, with hand planting system showing better seedling distribution. The number of defects per planted seedling was statistically similar for both planting systems. The major defects in the hand planting system were seedlings planted with soil-covered base and those planted out of the furrow center, which represented 72.8% of the total. With the machine system, these defects, in addition to non-planted and loose seedlings, represented 76.7% of the total. The height of the top portion was statistically different, both when planting and after one month. The survival of effectively planted seedlings after one month of age was statistically similar. Thus, we concluded that the quality of both planting systems did not vary within the standards that are acceptable for the forestation company. Machine planting system's productive time was 48.2%, and generated an estimated operational field capacity 60.0% less to that for the hand planting system. The average number of planted seedlings per worker by hour was inferred to be equal to 95 in the hand planting system, whereas it was equal to 205 in the machine system. The operational cost for the machine system was estimated to be 44.9% greater to that for the hand planting system, which is due to the low operational field capacity observed in the machine system.