Doctor of Philosophy / Department of Agronomy / P.V. Vara Prasad / Sorghum [Sorghum bicolor (L.) Moench] is a relatively drought- and heat-tolerant cereal crop. Global demand and consumption of agricultural crops for food, feed, and fuel is increasing at a rapid pace. To satisfy the growing worldwide demand for grain, production practices must be well optimized and managed. The objectives of the present study were: to optimize sorghum production by determining the best management practices (planting date, row spacing, seeding rate, hybrid maturity) for growth and yield, to evaluate the agronomic responsiveness of grain sorghum genotypes to nitrogen (N) fertilizer and to develop a partial financial budget to N fertilizer application based on best management practices. In order to meet these objectives, field experiments were conducted in 2009, 2010 and 2011 at Manhattan, Belleville, Ottawa, Hutchinson, Hays, at KSU Experiment Stations and Salina, and Randolph at Private Farms. Results indicated that early planting date (late May) and narrow row spacing (25 cm) providing the most equidistant spacing, produced better plant growth, light interception, yield components (number of grains per panicle, 300-grain weight), and biological yield. Results indicated that with increasing N rate, there was a proportional increase in chlorophyll SPAD meter reading, leaf color scores and number of green leaves. There was a significant difference among hybrids for N uptake, NUE and grain yield. However, there was no effect of N and no interaction between N and hybrid on grain yield. Over all, the genotypes with high NUE also had higher grain yield. Economic analysis using partial budget indicated that all N levels had positive gross benefit greater than control at all locations. However, the response varied across locations. Our research has shown that sorghum responds to changing management practices and opportunities exist to increase grain yield by optimizing planting date, seeding rate, row spacing, N application and selection of genotypes.

Sustainability of dairy production depends on their production of feed and finding ways to increase profitability through dairy production or even carbon (C) crediting and adding C inputs into the soil to sequester C. To increase farm profitability, dairy producers in Illinois, has intensified their feed production through integrating winter cereals such as winter cereal rye (Secale cereale) (WCR) into single season corn for silage (double cropping). Intensified cropping system allows for increased feed production, covering the soil year-round, and adding C inputs while minimizing nutrient loss mainly through runoff or leaching. Two management practices that improve the sustainability of corn silage – WCR double crop are harvesting date and nitrogen (N) management during the WCR phase of the production. This thesis has two main chapters. Chapter 1 evaluates the effect of harvesting date (five weekly harvest from late-March to early-May) with and without optimum N addition (0 vs. 47 kg N ha-1). Our objective was to evaluate harvesting date and spring N fertilization effect on WCR morphology, forage yield, nutrient removal, and quality. A quadratic model best explained an increase in WCR biomass in response to GDD (growing degree days) accumulation (R2 = 0.81). Increase in GDD linearly decreased WCR relative forage quality (RFQ). Benchmarking RFQ at 150 for dairy milk production indicates that WCR should be harvested at a GDD of 543 at which WCR plant height was 31.8 cm and dry matter (DM) biomass was 0.77 Mg ha-1. Benchmarking RFQ at 125 for heifer production indicated that harvest should occur at a GDD of 668 at which the WCR was 71 cm tall and its DM yield was 2.25 Mg ha-1. Nitrogen balances were negative at the no-N control treatment indicating a need for some N to maximize WCR yield. We found that a rate between 21 and 42 kg N ha-1 maximizes yields reflecting on slightly positive balances. Our results suggest that harvesting date can be predicted by GDD and should be adjusted for RFQ. We conclude that smaller than 42 kg N ha-1 N fertilizer is required for WCR production in soils with manure history and high soil organic matter (>30 g kg-1). Chapter 2 hypothesized that N fertilization of WCR as cover crop can increase nutrient recycling and C sequestration which offers C trading benefits to growers. We evaluated the effects of N fertilizer application in fall (0 vs. 56 kg N ha-1), and N fertilizer rates in spring (0, 23, 47, and 71 kg ha-1) on WCR dry matter (DM) biomass and cover crop quality. Results indicated that fall N fertilization had no effect on WCR biomass or quality reflecting on loss of applied N in the fall. Spring N application did not affect WCR biomass yield but increased N, P, and K concentrations, their uptake, C concentration, and decreased C:N and lignin:N ratios. We concluded that only spring N fertilization improves WCR cover crop benefits. Overall, we suggest that for high-quality forage, (RFQ at 150) WCR should be harvested at a GDD of 543 at which WCR plant height was 31.8 cm and dry matter (DM) biomass was 0.77 Mg ha-1. For RFQ of 125 (for heifer production), harvest should occur at a GDD of 668 at which the WCR was 71 cm tall and its DM yield was 2.25 Mg ha-1. Neither in fall nor in spring, N fertilization increase WCR C accumulation. Spring N fertilization reduces WCR C:N and lignin:N which are desirable for crop production.

This research included studies for transplant and field crop management with thepurpose of optimizing stand establishment, crop performance and nutritional quality ofartichoke (Cynara scolymus L.) grown in southwest Texas.Post-transplanting heat (35/20oC vs. 25/10oC, day/night temperatures) or drought[30% Water holding capacity (WHC) vs. 60% WHC] stress alone or in combinationsignificantly reduced shoot or/and root growth of artichoke seedlings. Combined heatand drought stresses strongly affected shoot water status and root growth. Results fromthis study imply that it is desirable to improve stand establishment by either conditioningthe seedlings to improve root growth or by preventing leaf dehydration by these stresses.Therefore, effects of plant growth regulators (PGR) on root growth and shoot waterstatus were examined.Ethylene regulators, including precursors or a releasing compound [DLmethionine(MET), 1-aminocyclopropane-1-carboxylic acid (ACC) and ethephone(ETH)], and inhibitors [amino-ethoxyvinylglycine (AVG) and 1-methylcyclopropene (1-MCP)] were applied to seedlings to evaluate their effect on root growth and development. ACC and ETH (1-100 M·L-1) enhanced root hair, root area and lateralroots (only with ETH at 30 M·L-1).The effects of film-forming antitranspirants and abscisic acid (ABA, 500-2000mg·L-1) foliar application on physiological responses, water status and hardiness ofartichoke transplants were examined under drought stress. ABA at 1000 mg·L-1enhanced drought tolerance of transplants which was associated with the maintenance ofshoot water status via stomatal closure. Film-forming antitranspirants were not effectiveto mitigate drought stress. These results suggest that ACC and ETH as root enhancers,and ABA as a plant water conditioner, could be useful PGR’s to enhance standestablishment in artichoke seedlings.Field artichoke performance in response to irrigation [50, 75 and 100% cropevapotranspiration (ETc)] and N (0-180 kg·ha-1) rates were investigated during threeseasons at Texas A&M AgriLife Research in Uvalde, TX. Irrigation was more effectivethan N rates to optimize artichoke yield. Yield reduction by 50% ETc was associatedwith a decrease in head number and weight. The highest yield was obtained with 100%ETc and 120 kg·ha-1 N. This study also showed that deficit irrigation significantlyimproved artichoke head quality, such as phenolic content, but with significant yieldlosses.

This research included studies for transplant and field crop management with thepurpose of optimizing stand establishment, crop performance and nutritional quality ofartichoke (Cynara scolymus L.) grown in southwest Texas.Post-transplanting heat (35/20oC vs. 25/10oC, day/night temperatures) or drought[30% Water holding capacity (WHC) vs. 60% WHC] stress alone or in combinationsignificantly reduced shoot or/and root growth of artichoke seedlings. Combined heatand drought stresses strongly affected shoot water status and root growth. Results fromthis study imply that it is desirable to improve stand establishment by either conditioningthe seedlings to improve root growth or by preventing leaf dehydration by these stresses.Therefore, effects of plant growth regulators (PGR) on root growth and shoot waterstatus were examined.Ethylene regulators, including precursors or a releasing compound [DLmethionine(MET), 1-aminocyclopropane-1-carboxylic acid (ACC) and ethephone(ETH)], and inhibitors [amino-ethoxyvinylglycine (AVG) and 1-methylcyclopropene (1-MCP)] were applied to seedlings to evaluate their effect on root growth and development. ACC and ETH (1-100 M·L-1) enhanced root hair, root area and lateralroots (only with ETH at 30 M·L-1).The effects of film-forming antitranspirants and abscisic acid (ABA, 500-2000mg·L-1) foliar application on physiological responses, water status and hardiness ofartichoke transplants were examined under drought stress. ABA at 1000 mg·L-1enhanced drought tolerance of transplants which was associated with the maintenance ofshoot water status via stomatal closure. Film-forming antitranspirants were not effectiveto mitigate drought stress. These results suggest that ACC and ETH as root enhancers,and ABA as a plant water conditioner, could be useful PGR’s to enhance standestablishment in artichoke seedlings.Field artichoke performance in response to irrigation [50, 75 and 100% cropevapotranspiration (ETc)] and N (0-180 kg·ha-1) rates were investigated during threeseasons at Texas A&M AgriLife Research in Uvalde, TX. Irrigation was more effectivethan N rates to optimize artichoke yield. Yield reduction by 50% ETc was associatedwith a decrease in head number and weight. The highest yield was obtained with 100%ETc and 120 kg·ha-1 N. This study also showed that deficit irrigation significantlyimproved artichoke head quality, such as phenolic content, but with significant yieldlosses.

Master of Science / Department of Agronomy / Antonio R. Asebedo / Sensor technology has become more important in precision agriculture, by real time sensing for site specific management to monitor crops during the season especially nitrogen (N). In Kansas N available in the soils can vary year to year or over a course of a year. The objective of this study was to compare current available passive (PS) and active optical sensor technologies (AOS) performance in regards to sky conditions effects and derive the NDVI (normalized difference vegetation index) relationship to wheat yield, as well as evaluate KSU optical sensor-based N recommendations against KSU soil test N recommendation system and sUAS (small unmanned aircraft systems) based recommendation algorithms with the PS and AOS platforms. Each year (2015-2016 & 2016-2017) five field trails across Kansas were conducted during the winter wheat crop year in cooperation with county ag agents, farmers, and KSU Agronomy Experiment Fields. Treatments consisted of N response curve, 1st and 2nd generation KSU N recommendation algorithms, sUAS based recommendation algorithms, and KSU soil test based N recommendations applied in the spring using N rates ranging from 0 to 140 kg ha⁻¹. Results indicate the Holland Scientific Rapid Scan and MicaSense RedEdge NDVI data was strongly correlated and generated strong relationships with grain yield at 0.60 and 0.57 R² respectively. DJI X3 lacks an NIR band producing uncalibrated false NDVI and no relationship to grain yield at 0.03 R². Calibrated NDVI from both sensors are effective for assessing yield potential and could be utilized for developing N recommendation algorithms. However, sensor based treatments preformed equal to higher yields compared the KSU soil test recommendations, as well as reduced the amount of fertilizer applied compared to the soil test recommendation. The intensive management algorithm was the most effective in determining appropriate N recommendations across locations. This allows farmers to take advantage of potential N mineralization that can occur in the spring. Further research is needed considering on setting the NUE (nitrogen use efficiency) in KSU N rec. algorithms for effects of management practice, weather, and grain protein for continued refinement.

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.

Thesis (MScAgric)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Three different pasture mixtures were established under irrigation at the Elsenburg research farm with the aim of devising nitrogen (N) management strategies for pastures in the Winelands sub-region of South Africa. The pasture mixtures were as follows: i) a mixed grass pasture consisting of perennial ryegrass (Lolium perenne), tall fescue (Festuca arundinaceae) and cocksfoot (Dactylis glomerata); ii) a grass-clover pasture consisting of perennial ryegrass, tall fescue, cocksfoot and red and white clover (Trifolium pratense and Trifolium repens); and iii) a grass-lucerne pasture consisting of perennial ryegrass, tall fescue and lucerne (Medicago sativa). The effect of fertiliser N on selected nutritive characteristics was also evaluated. The grass-legume pastures were subjected to two management strategies: the once-off application of N and the consecutive application of N over the autumn-early spring period. The reaction of the mixed grass pasture to applied N was mostly characterised by an interaction between the season of N application and N application rate. The productivity of the pasture in terms of the primary dry matter production (PDMP) and the total dry matter production (TDMP) was highest in spring and summer with the application of 60 – 80 kg N ha-1, and decreased in autumn and winter. There was a strong response of the winter residual dry matter production (RDMP) to N, which indicated that not all applied N was utilised during the first regrowth cycle, which might present a risk of nitrate being leached below the root zone. The botanical composition of the mixed grass pasture was determined by season of N application, and not N application rate. The tall fescue content was low over all seasons, presumably due to poor establishment and strong competition from accompanying species. In the cooler months perennial ryegrass and tall fescue was the dominant species, while in the warmer months cocksfoot was the main species. Nitrogen application also had a significant effect on the quality of the pasture, most notably the crude protein (CP) content. The response of the CP content was characterised by a strong interaction between season of N application and N application rate. Crude protein levels in excess of 22 % were recorded in autumn and winter with the application of 40 – 80 kg N ha-1. Other characteristics remained within the expected range. The response of the grass-clover and grass-lucerne pastures in terms of productivity and nutritive characteristics were mainly determined by the season of N application, and not N application rate. Productivity tended to be highest in autumn and early spring for both the once-off and the consecutive N application strategies, emphasizing the effect of temperature on pasture growth. The effect of season of N application and the N application rate on the botanical composition of the respective pastures were inconsistent over the two years of the study. The clover content tended to decrease in response to increasing rates of N, while the grass fraction was stimulated. Lucerne productivity decreased from autumn through winter and reached minimum levels in early spring, and was unaffected by fertiliser N rate. The legume component in both the grass-clover and grass-lucerne pastures remained above recommended levels of 20 – 40 % for optimum animal production, even when N was applied consecutively. The nutritive characteristics measured (dry matter (DM) content, CP, in vitro organic matter digestibility (IVOMD)) remained within the expected range, except the total CP content which was very high in the first year (> 30 %), although N application rate did not have a significant effect. Based on these findings, preliminary recommendations for N fertilisation (on low carbon soils) for a mixed grass pasture is 40 kg N ha-1 during autumn and winter and 60 kg N ha-1 in spring and summer. Based on the poor response of the grass-legume pastures to applied N it is doubtful whether fertilisation will lead to an economical advantage, but low rates of approximately 40 kg N ha-1 could be beneficial in a grass-clover pasture during autumn and late winter/early spring based on the relatively strong response of PDMP to N during this period. / AFRIKAANSE OPSOMMING: Drie verskillende weidingsmengsels is onder besproeiing te Elsenburg proefplaas gevestig met die doel om stikstof (N) bestuurstrategieë te ontwikkel vir aangeplante weidings in die Wynland distrik van die Wes-Kaap van Suid Afrika. Die weidingsmengsels was as volg: i) ‘n gemengde gras weiding bestaande uit meerjarige raaigras (Lolium perenne), langswenkgras (Festuca arundinaceae) en kropaargras (Dactylis glomerata), ii) ‘n gras-klawer weiding bestaande uit meerjarige raaigras, kropaargras, langswenkgras, wit - en rooi klawer (Trifolium pratense en Trifolium repens), en iii) ‘n gras-lusern weiding bestaande uit meerjarige raaigras, langswenkgras en lusern (Medicago sativa). Die effek van stikstof bemesting op sekere kwaliteitsaspekte van die onderskeie weidings was ook geëvalueer. Die gras-peulplant weidings was onderworpe aan twee bestuurstrategieë, naamlik die eenmalige toediening van N en die agtereenvolgende toediening van N bemesting tydens die herfs – lente periode. Die reaksie van die gemengde gras weiding op N bemesting was hoofsaaklik gekenmerk deur ‘n interaksie tussen die N bemestingspeil en die seisoen van N toediening. Die produktiwiteit van die weidings i.t.v. die primêre droeëmateriaal produksie (PDMP) en die totale droeëmateriaal produksie (TDMP) was die hoogste in die lente en somer met die toediening van 60 – 80 kg N ha-1 en het in herfs en winter afgeneem. Daar was n sterk respons van die winter residuele droeëmateriaal produksie (RDMP) teenoor N, wat aandui dat nie alle toegediende N tydens die eerste hergroei periode benut was nie en dus ‘n moontlike risiko van loging inhou. Die botaniese samestelling van die gemengde gras weiding was deur die seisoen van N toediening bepaal, en nie die N bemestingspeil nie. Die langswenkgras inhoud was baie laag in alle seisoene, vermoedelik a.g.v. swak vestiging en sterk kompetisie van gepaardgaande spesies in die mengsel. Tydens die koeler seisoene van die jaar was meerjarige raaigras en langswenkgras die dominerende spesies, terwyl kropaargras tydens die warmer maande gedomineer het. Stikstof toediening het ook ‘n betekenisvolle effek op die kwaliteit van die weiding gehad, veral die ru-proteien (RP) inhoud. Die respons van RP was weereens gekenmerk deur ‘n betekenisvolle interaksie tussen die seisoen van N toediening en die N peil. Ru- proteien vlakke hoër as 22% was tydens herfs en winter waargeneem met die toedieningspyle van 40 – 80 kg N ha-1. Ander kwaliteits- eienskappe het binne normale perke gebly. Die respons van die gras-klawer en gras-lusern weidings in terme van produktiwiteit en kwaliteitseienskappe was hoofsaaklik deur die seisoen van N toediening bepaal, en nie deur die N bemestingspeil nie. Die produktiwiteit was die hoogste tydens herfs en vroeë lente vir beide die eenmalige en die herhaalde N toedieningsstrategieë. Hierdie bevindinge beklemtoon die belangrike effek van temperatuur op die groei en produksie van weidingsgewasse. Die effek van seisoen van N toediening en N peil op die botaniese samestelling van die gras-peulgewas weidings was inkonsekwent oor die twee jare van die studie. Die klawer-fraksie was geneig om af te neem soos wat die N peil toegeneem het, terwyl die gras-fraksie toegeneem het. Die lusern-inhoud het van herfs tot lente afgeneem en was ongeaffekteer deur die N peil. Die peulgewas-inhoud van beide weidingsmengsels was deurentyd hoër as die voorgeskrewe minimum vlak van 20 – 40%, selfs met opeenvolgende N-toediening. Die kwaliteitseienskappe gemeet in die studie (droeëmateriaal (DM) inhoud, RP en in vitro organiese materiaal verteerbaarheid (IVOMV)) het binne normale perke gebly, behalwe die totale ru-proteien (TRP) inhoud wat baie hoog was tydens die eerste jaar (>30%), alhoewel dit nie deur die N peil beinvloed was nie. Aan die lig van bogenoemde bevindinge is die voorlopige aanbeveling vir N- bemesting (op lae koolstof gronde) van ‘n gemengde grasweiding 40 kg N ha-1 tydens die herfs en winter en 60 kg N ha-1 tydens lente en somer. Gebasseer op die swak respons van die gras-peulgewas weidings op toegediende N, is dit twyfelagtig of N toediening enige ekonomiese voordeel vir die boer sal inhou. Gebaseer op die relatiewe sterk respons van die gras-klawer PDMP op toegediende N tydens herfs en laat winter/vroeë lente kan dit moontlik voordelig wees om lae N-vlakke van ongeveer 40 kg ha-1 tydens hierdie seisoene toe te dien.

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