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Potential new sources of phosphorus (P) fertilizer are the recovered P from livestock wastewater through chemical precipitation and the ash from combusting animal manures. Although most of the research on P losses from conservation tillage include high water-soluble P compounds from commercial fertilizer sources, information on the use of non-conventional, low water-soluble, recycled P sources is scarce. Particularly for sandy soils of the United States (US) Southeastern Coastal Plain region, research driven information on P loss into the environment is needed to determine recommendations for a direct use of new recycled P sources as crop P fertilizers. The objective of this study is to investigate the potential P runoff from sandy soils under conservation tillage, fertilized with recovered P from liquid swine manure and turkey litter ash in comparison with commercial P fertilizer triple superphosphate (TSP). The field study included two typical sandy soils of the US Southeastern Coastal Plain region, the Noboco and Norfolk. Simulated rain corresponding to the annual 30-min rainfall in the study site (Florence County, South Carolina) was applied to plots treated with recovered P from liquid swine manure, turkey litter ash, and TSP, including a control with no P added. The runoff was monitored and sampled every 5 min during the test and composite soil samples were collected from the top (0-15 cm) and subsurface (15-30 cm) soil layers in each plot. Laboratory analyses were conducted to quantify both total P (TP) and soluble reactive P (SRP) in runoff samples, and the soil test P in the soil layers. Two-way analyses of variances show significant treatment effects on both TP and SRP runoff. The quantities of SRP runoff from plots treated with the recovered P from swine manure and turkey litter ash represent respectively 1% and 7-8% of SRP runoff from plots treated with TSP. Hence, the use of the recovered P materials as crop P fertilizers through surface broadcast application present less environmental risks compared to commercial TSP.

HighlightsA decision support system using the USDA-ARS Irrigation Scheduling and Supervisory Control and Data Acquisition (ISSCADA) system was evaluated for spatially managing corn irrigation in the U.S. Eastern Coastal Plain.The ISSCADA system was compared to traditional scheduling methods based on measured soil water potentials.The ISSCADA system with feedback on allowable soil water depletion shows potential as a tool for growers for managing variable-rate irrigation systems.Abstract. Variable-rate irrigation (VRI) systems are capable of applying different water depths both in the direction of travel and along the length of the irrigation system. VRI systems maybe useful for improving crop water management and efficiency. Although VRI technology is available and has high grower interest, it has had limited adoption. To address this, researchers have developed a decision support system that uses remote sensing of plant, soil, and microclimate to schedule VRI irrigations. In this research, we evaluated the use of the USDA-ARS Irrigation Scheduling and Supervisory Control and Data Acquisition (ISSCADA) system for spatially managing corn irrigation in the U.S. Eastern Coastal Plain. The ISSCADA system consists of center pivot mounted infrared thermometers (IRT) to measure crop canopy temperatures and in situ soil water sensors. An integrated crop water stress index (iCWSI) was calculated from the canopy temperatures. The ISSCADA system analyzes the iCWSI and soil water measurements to provide an irrigation recommendation. The ISSCADA system was evaluated using (1) iCWSI values and (2) a hybrid ISSCADA system that incorporated both iCWSI values and soil water depletion criteria. These ISSCADA treatments were compared to traditional irrigation management using measured soil water potentials. The ISSCADA system was evaluated for four years. In 2016 and 2017, corn yields and water use efficiency were not significantly different between the irrigation treatments due to adequate rainfall during the growing season. In 2018 and 2019, mid-season drought conditions and sporadic rainfall patterns required frequent irrigations. In both years, the irrigation treatment corn yields were not significantly different from each other but were greater than the rainfed yields. In 2018, the irrigation treatments produced corn yields of 10.7, 10.4, and 10.1 Mg ha-1 for the hybrid, ISSCADA, and SWP treatments, respectively. Over the four-year study, the water use efficiencies of the irrigation treatments were not significantly different from each other or the rainfed treatment and ranged from 16.6 to 22.7 kg ha-1 mm-1. In the two years that the hybrid ISSCADA system was used for managing irrigations, it produced higher corn yields and required less irrigation than the standard ISSCADA treatments. Results from this experiment will help to evaluate and refine the ISSCADA system to provide a tool for growers to use in managing spatial irrigation with VRI systems. Keywords: Crop water stress, Decision support system, Variable rate irrigation.

Potential new sources of phosphorus (P) fertilizers are the recovered P from livestock wastewater through chemical precipitation and the ash from combusting animal manures. These P-rich materials have low water solubility. Most of the research on P losses from conservation tillage include commercial fertilizer sources that have a high-water soluble P content but information on the use of non-conventional, low water soluble, recycled P sources is scarce. The objective of this study was to investigate the potential P runoff from conservation tillage fertilized with phosphates recovered from turkey litter ash and liquid swine manure in comparison with commercial P fertilizer triple superphosphate (TSP). Simulated rain corresponding to the annual 30-minute rainfall in the study site (Florence, South Carolina) was applied to plots treated with three P fertilizer sources and one control. The P fertilizer sources included turkey litter ash (a bio-energy byproduct), granulated recovered P from liquid swine manure, and TSP. The runoff was monitored and sampled every 5 minutes during the test. Laboratory analyses were conducted to quantify the P wash-off in runoff samples. Results show that the quantity of P wash-off from the plots treated with turkey litter ash and the recovered P from swine manure were respectively 10 and 15 times lower than the triple super phosphate plots. These results sustain the use of the turkey litter ash and recovered P from swine manure as crop P fertilizer through surface broadcast application.

The soil nitrogen (N) availability and urease activity (UA) in a humid ecosystem with variable rainfall distribution and poor soil fertility are not well understood. A complete appreciation of N cycling in the soil&ndash, water&ndash, plant continuum is needed to better manage N and water in regions that will be strongly affected by climate change. A sorghum (Sorghum bicolor L.) study located in Florence, South Carolina, USA, was conducted using a variable-rate pivot system. We hypothesized that supplemental irrigation (SI) and N would enhance UA and N uptake while minimizing the concentration of N in porewater (TINW). The aim of the study was to assess the impact of SI (0, 50, and 100%) and N fertilization (0, 85, and 170 kg N ha&minus, 1) on: UA, total N (TNS), total inorganic N (TINS), TINW, and N uptake of sorghum. Results support our research hypothesis. The greatest UA was from 0% SI and 170 kg ha&minus, 1 (18.7 &micro, g N g&minus, 1 ha&minus, 1). Porewater N (mg L&minus, 1), when averaged across SI and N showed a significantly lower concentration at lower soil depth (9.9 &plusmn, 0.7) than the upper depth (26.1 &plusmn, 2.4). The 100% SI had the greatest biomass N uptake (NUPB) of 67.9 &plusmn, 31.1 kg ha&minus, 1 and grain N uptake (NUG) of 52.7 &plusmn, 20.5 kg ha&minus, 1. The greatest NUPB (70.9 &plusmn, 30.3 kg ha&minus, 1) and NUG (55.3 &plusmn, 16.5 kg ha&minus, 1) was from the application of 170 kg N ha&minus, 1. Overall, results showed that proper use of water and N enhanced soil N dynamics, and improved biomass productivity and N uptake of sorghum.

Poor rainfall distribution and poor soil fertility in the humid coastal plain region may affect grain crop production. Nitrogen insufficiency and water stress can both reduce crop yield, but little information is available on whether supplemental irrigation (SI) and N fertilization can alleviate both water stress and nutrient deficiency in humid regions. A field sorghum [Sorghum bicolor (L.) Moench] study was conducted under a variable-rate center pivot. The objective of our study was to determine the combined effects of N fertilization (0, 85, and 170 kg N ha–¹) and SI (0, 50, and 100% of the full irrigation rate) on aboveground biomass (AB), nitrogen uptake (NU), and nitrogen-use efficiency (NUE) of two varieties (VAR) of grain sorghum in coastal plain region of the United States. Aboveground biomass and NU varied with SI (p ≤ 0.001) and levels of N (p ≤ 0.001). In irrigated treatments, the rates of 85 and 170 kg N ha–¹ resulted in significantly higher AB, NU, and NUE. Averaged across years, VAR, N and SI, grain sorghum applied with 170 kg N ha–¹ and 100% SI had the greatest AB of 3997 kg ha–¹. Sorghum with 85 and 170 kg N ha–¹ and 100% SI treatment had the greatest NUE of 60.5 and 57.1%, respectively. Our results support our hypothesis that negative impacts of water stress and nutrient deficiency could be mitigated by SI and N fertilization. Effective water use in irrigation and maintaining a sufficient amount of N will improve the AB, NU, and NUE of grain sorghum.

Over the last two decades, signs of precipitation irregularity were frequently reported across the Southeastern United States (US). Even though the region receives a relatively high annual precipitation, the precipitation events are not equally distributed in the time and space. Hence, rainfed agriculture, a common practice in the region is threatened by changes in precipitation frequencies during the crop growing seasons. With this situation, a better understanding of the actual patterns of precipitation irregularity is needed to support the local agriculture. This study uses a spatial regionalization approach to delineate precipitation regions for an area spanning the states of South Carolina, North Carolina, and Georgia. The data used include time-series of seasonal precipitation totals and seasonal numbers of precipitation events >5 mm over the period 1960–2017. A regionalization method which combines principal components and cluster analyses was applied to 208 precipitation stations selected across the study region. Finally, three precipitation regions were delineated based on statistics and similarity criteria. A comparative analysis of these three regions shows significant differences in the seasonal precipitation totals and the seasonal number of precipitation events. In addition, the differences were examined using a probabilistic approach. As a result, tables of probabilities and seasonal precipitation characteristics (precipitation totals and number of events >5 mm) were generated for each region. These tables could provide information about the chances of precipitation deficits or excesses relatively to a crop and henceforth be useful for agricultural water use planning.

The quantity and availability of N from green manures will considerably affect the N management of a succeeding cotton (Gossypium hirsutum L.) crop. This study was conducted to determine the N supplying capacity of crimson clover (Trifolium incarnatum L.), Austrian winter pea [Pisum sativum subsp. arvense (L.) Poir.], and rye (Secale cereale L.) to cotton and their influence on cotton yield and fiber properties. Green manure treatments (and a fallow check) with fertilizer N levels of 0, 56, 112, and 168 kg ha −1 were compared for 3 yr on a Norfolk loamy sand (fine-loamy, siliceous, thermic Typic Kandiudult). Soil moisture at planting was similar among the four green manure treatments. At the 0 N level, the legumes generally had higher soil NO 3 -N than rye or fallow [...]