Master of Science / Department of Agronomy / Johanna A. Dille / An opportunity for postemergence (POST) grass weed control has recently been approved with ALS-resistant grain sorghum, however, grass weed emergence timing and crop tolerance to grass competition are not well understood. To address the importance of POST application timing, a critical period of weed control (CPWC) for grass competition in grain sorghum was developed. Field experiments were established near Manhattan and Hays, KS in 2016 and 2017, and near Hutchinson, KS in 2017 to determine the CPWC. Each site provided a different grass species community. A total of ten treatments were included, with four treatments maintained weed-free until 2, 3, 5, or 7 weeks after crop emergence, four treatments receiving no weed control until 2, 3, 5, or 7 weeks after crop emergence, and two treatments were maintained weed-free or weedy all season. Treatments did not influence grain yield at Hutchinson because of a lack of season-long weed emergence. At Hays the CPWC began at crop emergence and ended 28 days later. At Manhattan the CPWC began 27 days after emergence and continued through grain harvest. The CPWC in grain sorghum depends on rainfall and competitive ability of the weed species. The start of the CPWC began when weeds emerged, thus a POST application should be targeted 14 to 21 days after emergence of grain sorghum. Emergence and development of large crabgrass, barnyardgrass, shattercane, and giant, green, and yellow foxtails were studied near Manhattan, KS after seeding on April 11, 2017. Barnyardgrass had the longest duration of emergence, beginning at 180 GDD after seeding and continuing through July. Large crabgrass had the shortest duration of emergence from 325 to 630 GDD after seeding. In general, all grasses began to emerge in late April and most species completed 90% emergence by early June. Grain sorghum is typically planted at this time, so grass weed control prior to planting is critical. Palmer amaranth is a troublesome weed in double-crop grain sorghum production fields in Kansas. The presence of herbicide-resistant populations limits options for weed management. Field experiments were conducted to evaluate 14 different herbicide programs for the management of atrazine-resistant Palmer amaranth in double-crop grain sorghum at Manhattan and Hutchinson, KS in 2016 and 2017. Programs included eight PRE only and six PRE followed by POST treatments. Programs that had very long chain fatty acid-inhibiting herbicides provided greater control of atrazine-resistant Palmer amaranth by three weeks after planting sorghum. Programs of PRE followed by POST provided greater control of both atrazine-resistant and -susceptible Palmer amaranth by eight WAP compared to PRE alone. These results illustrate the value of residual herbicides, as well as an effective postemergence application, in double-crop grain sorghum. Early season grass and Palmer amaranth control with the use of residual herbicides such as very long chain fatty acid-inhibitors provide a competitive advantage to grain sorghum. Utilizing weed emergence patterns to time effective POST applications, in unison with residual herbicides, will provide season-long weed control in Kansas grain sorghum fields.

Grain sorghum [Sorghum bicolor (L.) Moench] varieties fail to reach maturity in North Dakota’s short and cool growing season. The study objective was to evaluate seeding date and white grain sorghum genotypes. A randomized complete block design study was conducted at Carrington, Oakes, and Prosper, ND, in 2018 and 2019. Genotypes included two commercial hybrids and four open-pollinated genotypes. Reaching heading and anthesis, hybrids required more heat units (GDDs), compared with the open-pollinated genotypes. Highest grain yield was obtained from the first and second seeding dates. Earlier-maturing open-pollinated genotypes maintained yield across seeding dates, whereas yield was reduced at later dates for the longer maturity hybrids. Hybrids produced the highest number of kernels per panicle at the first seeding date with fewer seeds at each successive seeding date. Although the open-pollinated genotypes out-yielded the hybrids at later seeding dates, the risk of lodging is too great to recommend their commercialization.

Grain sorghum is a drought tolerant crop used in the Mid-south region in rotation with corn, cotton, soybeans, and corn. In 2015 and 2016, research was conducted to determine the influence of insecticide treatment, planting date, planting population, hybrid, and environmental temperatures on sugarcane aphid, Melanaphis sacchari (Zehntner), populations and yield in grain sorghum, Sorghum bicolor (L.) Moench. In general, cooler temperatures had a negative effect on sugarcane aphid control with sulfoxaflor and flupyradifurone. Additionally, there was a negative relationship between grain sorghum plant population and sugarcane aphid densities per plant. These data suggest management of sugarcane aphid with insecticide seed treatments and foliar sprays is critical for maximizing grain sorghum yields. Additionally, growers should wait for warmer temperatures to ensure optimum control.

Master of Science / Department of Agronomy / Curtis R. Thompson / Curtis R. Thompson / Postemergent herbicide options for grain sorghum are limited and increasingly challenged by the development of herbicide resistant weeds. The herbicide pyrasulfotole & bromoxynil (P&B) was evaluated for potential use in grain sorghum and for control of a suspected HPPD-resistant Palmer amaranth population. Field experiments were conducted near Manhattan and Rossville, KS, to evaluate grain sorghum response to P&B with and without 2,4-D applied to growth stages from 1-leaf through the flag leaf stage and tankmixed with 2,4-D ester, amine, or dicamba applied to 3- and 6-leaf sorghum. The addition of 2,4-D ester did not reduce sorghum injury from P&B alone. Increasing the rate of P&B increased injury. Treatments applied to 1- and 4-leaf sorghum were injured the most. All P&B treated sorghum, regardless of timing, yielded 8 to 20% less than the untreated check. Pyrasulfotole & bromoxynil applied alone or with dicamba injured sorghum less than 2,4-D applied at 3- or 6-leaf. Increasing the rate from 140 to 280 g ha[superscript]-1 2,4-D amine or ester increased injury by 6 to 11%. Yields were lowest when P&B was applied with 2,4-D amine at 140 g ha[superscript]-1 and 2,4-D amine or ester at 280 g ha[superscript]-1 compared to all other treatments. Increasing the rate of growth regulator herbicides decreased yields by 8% and did not reduce crop injury from P&B alone. Greenhouse and field experiments were conducted to evaluate the response of two suspected P&B-resistant (R1 & R2) and one susceptible (S) Palmer amaranth population to P&B, atrazine, and tembotrione. Herbicides were applied when plants were 7 to 19 cm tall. The S population was controlled with less than field use rates. A resistance index (RI) of 4.8 to 11.0 was determined for R1 and R2 in greenhouse and field experiments. Tembotrione controlled 100% of S in all experiments, while providing 63 to 86% injury to R1 and R2 populations. Atrazine did not control the resistant populations. Pyrasofotole & bromoxynil will be an valuable tool for weed control in sorghum, however, Palmer amaranth populations exist that will not be controlled.

Master of Science / Department of Agronomy / Johanna Dille / Nitrogen (N) fertilizer intended for the crop may benefit highly competitive weeds to the detriment of the crop. A field experiment was conducted in 2009 to determine the influence of increasing N fertilizer rates and increasing Palmer amaranth densities on weed biomass and grain sorghum biomass and yield. Three rates were 0, 67, and 134 kg N ha-1 and natural populations of Palmer amaranth were thinned to densities of 0, 0.5, 1, 2, 4, and 8 plants m-1 of row. Palmer amaranth biomass increased as weed density and N rates increased. Weed-free grain sorghum yields were similar across all three N rates, and parameter estimates of yield across Palmer amaranth densities were not different between N rates. Based on the parameter estimates from the rectangular hyperbola model, initial slope (I) as density approached zero was 16%. Maximum expected yield loss (A) at high Palmer amaranth densities was 68%. Palmer amaranth showed a high response to N and the higher N rate increased the ability of the weed to reduce grain sorghum yield. A greenhouse experiment was conducted to determine the influence of six N rates on growth of six selected plant species, including grain sorghum, soybean, yellow foxtail, velvetleaf, Palmer amaranth and shattercane. Covariance analysis was performed with N rate as a covariate. Biomass of all species increased as N rate increased in both runs of the study. Soybean responded the least to N rate of all species in regards to biomass, height and leaf area production. In the first run, the biomass of three grass species (grain sorghum, yellow foxtail, shattercane) had similar estimates of slope and intercept of biomass across N rates. In the second run, the biomass slopes of grain sorghum and shattercane differed from soybean and were the only slopes that differed between species. Palmer amaranth had the highest rate of response as N increased but slopes of height were similar for Palmer amaranth, grain sorghum and shattercane. Soybean leaf area slopes were different from grain sorghum, yellow foxtail, and velvetleaf, but all other slopes were not different among species. Addition of N to grain sorghum increased weed growth and resulted in more yield loss as a result of weed density. The greenhouse study demonstrated that grain sorghum and Palmer amaranth increased in response similarly to the addition of N. Alternative N fertilizer management could play a role in minimizing Palmer amaranth impacts in grain sorghum production.

Master of Science / Department of Agronomy / David B. Mengel / Grain Sorghum (Sorghum bicolor) is one of the most drought and stress tolerant crops grown in Kansas. For this reason, much of the sorghum is grown in high risk environments where other crops are more likely to fail or be unprofitable. Efficient sorghum cropping systems should not only produce high yields and use inputs such as nitrogen efficiently, but they should also remove as much risk as possible for a successful crop, and give farmers more flexibility in making input decisions. The price of nitrogen (N) fertilizer has increased substantially in recent years. Current retail prices for commonly used N fertilizers range from $0.88 to $1.50 per kilogram of N in Kansas. Thus, a farmer could easily invest $50-$100 per hectare in N, depending on the rate of N needed and the source used. Practices which allow farmers to assess crop potential as late as possible after planting before applying costly inputs like fertilizer, can increase the potential for a profitable return on those inputs in risky environments. Currently, most sorghum growers routinely apply all the N fertilizer prior to planting, sometimes as much as 6 months prior. The current Kansas State University (KSU) nitrogen recommendation is yield goal based and performs well when the grower is able to predict yield six months or more in advance of harvest. However, yield is quite variable and difficult to predict. Because long range weather and yield predictions are not very reliable, could deferring making N application decisions until later in the season when yield can be more accurately predicted reduce risk? Can the use of active sensors provide a better estimate of yield potential and nitrogen needs sometime after planting? If they can, how late can the decision be made and how best should the fertilizer N be applied? Several studies were conducted throughout Kansas to look at the effect of N rate, N application timing (pre-plant, side dress, or combinations of the two) and method of application on sorghum yield and N use efficiency. The studies were also designed to examine the potential of using optical sensors to predict optimum N rate for post-planting applications as a means of avoiding the use of soil tests to estimate soil N contributions. The objectives of this research were: a. to validate the KSU N fertilizer recommendations for grain sorghum grown in rotation with crops such as soybeans and wheat, b. to determine the effect of both preplant and midseason N applications on the growth and yield potential of grain sorghum, and to determine the optimal timing and method for midseason N applications on grain sorghum, and, c. to assess the potential of optical sensing of the growing crop to refine N recommendations using in-season applications during the growing season. This thesis will summarize the results from the various experiments we completed to achieve these objectives. The KSU N fertilizer recommendations for grain sorghum may need some revisions. This research suggests that including coefficients relating to N use efficiency may be necessary to get more accurate N recommendations. Both pre-plant and midseason N applications increased the yield of grain sorghum whenever a response to N was observed. There was no negative effect of applying all the nitrogen midseason at 30-40 days after planting when compared to pre-plant applications. Injecting nitrogen fertilizer below the soil surface had higher yields than other methods of midseason N applications such as surface banding or surface broadcasting, especially when a significant rainfall event did not occur within a few days of application. The optical sensors used in this study were very effective at making N recommendations 30-40 days after planting. These sensors will provide for more accurate N recommendations compared to the current soil test and yield goal method.

Master of Science / Department of Agronomy / P. V. Vara Prasad / Grain sorghum (Sorghum bicolor L. Moench) is the fourth most important cereal crop grown throughout the semi-arid regions of the world. It is a staple food crop in Africa and Asia, while it is an important feed crop in the United States (US). More recently it is increasingly becoming important as a potential bioenergy feedstock crop around the world. The state of Kansas is the largest producer of grain sorghum in the US and contributes 40% of the total production. Drought is one of the major environmental factors limiting sorghum production in the semi-arid regions of the US, Asia and Africa. It is estimated that global crop losses due to drought stress exceed $10 billion annually. In crop production, drought stress can be classified into pre- or post-flowering. Even though the world collections of sorghum contain over 35,000 accessions, the genetic base currently used in breeding programs is very small (about 3%). Thus, it is important to identify diverse breeding lines for crop improvement. The diversity (association) panel consisting of 300 sorghum lines from all over the world was assembled for trait evaluation and association mapping. In this research these lines were grouped into the five major races (Figure 1) and 10 intermediate races of sorghum. The objectives of the research are to: (i) quantify the performance of the diversity panel under field conditions in Kansas, (ii) identify critical physiological traits affected by drought at both pre- and post-flowering stages of sorghum development, (iii) identify the most sensitive stage to drought stress during the reproductive phase of sorghum development and, (iv) test the feasibility of using a chlorophyll fluorescence assay (CVA) as a tool for identifying stay-green lines in grain sorghum during early stages of crop development. Field experiments were conducted in 2006 and 2007 in two locations in Kansas (Manhattan and Hays) under rain fed and irrigated conditions for the association panel. Objectives (iii) and (iv) were achieved with controlled environment experiments conducted in the greenhouse at the agronomy department, Kansas State University in 2006 and 2007. Results showed that there was large genetic variability among and within different races in the diversity panel for growth, physiological traits and yield components. Some genotypes showed yield stability across the different environments that were investigated. Drought significantly decreased seed number and harvest index across genotypes and races. In grain sorghum the period prior to flowering (panicle initiation) was the most sensitive stage to drought stress, in terms of its effect on seed-set, during reproductive development. A cell viability assay showed that there were significant differences in the loss of cell viability between leaf sample of stay green and non-stay green genotypes when leaf samples are collected in the morning and subjected to high respiratory demand. Therefore the chlorophyll fluorescence assay has potential as a tool for stay green trait screening at early stages of growth in grain sorghum.

Master of Science / Agronomy / Robert Aiken / Xiaomao Lin / Productivity of water-limited cropping systems can be reduced by untimely distribution of water as well as cold and heat stress. The research objective was to develop relationships among weather parameters, water use, and grain productivity to produce production functions to forecast grain yields of grain sorghum and winter wheat in water-limited cropping systems. Algorithms, defined by the Kansas Water Budget (KSWB) model, solve the soil water budget with a daily time step and were implemented using the Matlab computer language. The relationship of grain yield to crop water use, reported in several crop sequence studies conducted in Bushland, TX; Colby, KS and Tribune, KS were compared against KSWB model results using contemporary weather data. The predictive accuracy of the KSWB model was also evaluated in relation to experimental results. Field studies showed that winter wheat had stable grain yields over a wide range of crop water use, while sorghum had a wider range of yields over a smaller distribution of crop water use. The relationship of winter wheat yield to crop water use, simulated by KSWB, was comparable to relationships developed for four of five experimental results, except for one study conducted in Bushland that indicated less crop water productivity. In contrast, for grain sorghum, experimental yield response to an increment of water use was less than that calculated by KSWB for three of five cases; for one study at Colby and Tribune, simulated and experimental yield response to water use were similar. Simulated yield thresholds were consistent with observed yield thresholds for both wheat and sorghum in all but one case, that of wheat in the Bushland study previously mentioned. Factors in addition to crop water use, such as weeds, pests, or disease, may have contributed to these differences. The KSWB model provides a useful analytic framework for distinguishing water supply constraints to grain productivity.

Neonicotinoid seed treatments are widely used and highly effective against early season insect pests of all row crops throughout the Mid-South region of the United States. An analysis was performed to determine the value of neonicotinoid seed treatments across multiple trials in soybean, Glycine max L.; corn, Zea mays L.; cotton, Gossypium hirsutum L.; and sorghum, Sorghum bicolor L. production systems across the mid-southern region. Neonicotinoid seed treatments provided significant yield and economic increases when utilized the majority of the time. A second experiment was performed to determine the value of various insecticide classes when utilized in an overall systems approach when managing cotton insect pest in the Delta and Hills region of Mississippi. When all classes of insecticides were used in rotation, significant yield and economic benefits were observed in the Delta Region compared to treatment scenarios where some insecticide classes were omitted.

Grain sorghum provides energy-rich seeds for waterfowl. I conducted experiments in 22 sorghum fields in Arkansas, Mississippi, and Louisiana during falls 2006 – 2007 to evaluate abundance of ratoon grain (i.e., second crop after harvest), waste grain, and natural seeds. I also conducted surveys of wintering waterfowl in flooded croplands and moist-soil wetlands to evaluate if ducks and geese differentially used habitats. Fertilized plots in 2007 produced >4 times more ratoon grain (x = 219.57 ± 39.65 [SE] kg/ha) than other treatments. Fertilized plots in southern regions of my study area produced ~5 times more ratoon grain (x = 262.93 ± 50.28 kg/ha) than others. Mallards and other ducks used moist-soil wetlands (x >65 ducks/ha) more than other habitats. I did not observe geese using flooded sorghum. I recommend not manipulating sorghum stubble after harvest, fertilizing, and flooding it after ratoon grain has matured, and integrating moist-soil wetlands into agricultural lands.