Organic growers use a wide range of organic fertilizers and materials to supply nutrients and meet plant demand of N. These products range from commercially processed animal and plant byproducts to composts and poultry litters. To better synchronize N release with plant demand, we investigated the rate and pool of potentially mineralizable N from 22 commercial, organic fertilizers; 15 poultry litters; and 11 composts. Fertilizers and organic materials were mixed with soil and inorganic N was measured over 99 days under optimal conditions (50% estimated water holding capacity and 30°C). Net N mineralized from the organic fertilizer or material was determined and fit to first‐order kinetics to determine the rate of mineralization (k) and the pool of mineralizable nitrogen (N0). Net N mineralized ranged from 25–93%, 10–55%, and 1–5% of the organic N applied for the fertilizers, poultry litters, and composts that mineralized, respectively. The pool of mineralizable N was accurately predicted from the initial total N of the materials, but no characteristics predicted the rate constant, k. Using a grouped approach based on product type and the percentage of N mineralized to determine k, we were able to predict net mineralized for fertilizers (R2 = 0.84) and poultry litters (R2 = 0.62).

Industrial hemp (Cannabis sativa) cultivars used for flower, fiber, or seed production are usually considered short-day plants and flower in response to photoperiod. However, some cultivars of hemp are day-neutral, where flower induction may be independent of daylength. Day-neutral cultivars of hemp were planted before recommended dates and studied in field experiments conducted in Watkinsville, GA, in Spring 2020 and 2021. Day-neutral cultivars (Pipeline and Maverick) and photoperiod-sensitive cultivars (Von and Whitehouse Cherry) were planted on 9 and 25 Apr and 11 and 28 May to determine the impact of planting date on hemp flower yield and quality. Planting date did not impact yield of the photoperiod-sensitive cultivars, but yields of day-neutral cultivars decreased as planting date progressed. Average yields of photoperiod-sensitive plants were greater than the day-neutral cultivars in both study years. Cannabinoid concentrations in flowers were affected by cultivar and study year but were not impacted by planting date. Cannabidiol was the most prevalent cannabinoid in flower tissue with concentrations ranging from 6.5% to 10.5%. Flower biomass yields suggest that the spring hemp planting season may be extended using day-neutral cultivars in the southeastern United States.

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Prediction of N mineralization is dependent on accurate rate correction factors and the ratio of the change of the rate coefficient of mineralization for every increase in temperature of 10°C (Q10) based on temperatures observed in the region. Few studies have investigated N mineralization in soils receiving repeated applications of manures at low temperatures. This study determined that manure additions may lead to larger Q10 values at low temperatures and growing degree‐days may aid in predicting N release from these soils. There are currently no tools available to help predict N mineralization for the silty soils found in southern Idaho receiving repeated manure applications. This experiment aimed to determine the effect of temperature on N mineralization from control and manured soils, develop N mineralization rate correction factors for temperature [ratio of the change in the rate coefficient of mineralization for every 10°C increase (Q10) and temperature factors], and create a simple model for predicting N mineralization as a function of growing degree‐days. Manured and control soils underwent a 49‐d laboratory incubation at five temperatures (–14, 4, 10, 23, and 30°C); soil inorganic N concentration was determined at 0, 1, 3, 5, 7, 13, 20, 28, 35, 42, and 49 d. Net N mineralization was fitted to a zero‐order model, where the rate coefficient (k) values for the manured soil ranged from 0.017 to 1.28 mg kg–1 soil d–1 over the five temperature treatments, whereas k in the control measured 0.028 to 0.53 mg kg–1 soil d–1. The calculated Q10 values from –14 to 30°C were 2.7 and 2.0 for the manured and control soils respectively. At low temperatures (–14 to 4°C), the Q10 for manured soil was 5.1 compared with 1.5 for the control. This suggests that manure additions may lower the temperature threshold for N mineralization under near frozen soil conditions. Manure treatment effects on the temperature factor were not observed, suggesting that manure application history may not need to be considered when developing temperature factor coefficients for N mineralization models.

Laboratory incubations of four broiler litter (BL) samples at 30°C were performed to investigate the effect of water content on the decay of uric acid nitrogen (UAN) and xanthine nitrogen (XN). UAN and XN concentrations increased in all samples during a period of 1 to 8 d before declining for the remaining 30 d. The increases may be the result of guanine and adenine catabolism. The slopes of linear equations fit to the natural log of the observations from 16 sampling points over 38 d were compared using the GLM procedure in SAS and results indicate that both UAN and XN decay significantly ( = 0.05) more rapidly with increasing water content (θ). A second study showed significant effects in one of three samples on the decay rate of UAN with additions of flue-gas desulfurization (FGD) gypsum or alum at a water content of 750 g kg BL. The decay rate of XN was not significantly affected. Finally, a simple two-point sampling study on the effect of water potential for the estimation of first order rate equation constants showed a positive relationship between the rate of UAN and XN decay over 28 d as a function of water potential (ψ): UAN = 0.0054 × ψ + 0.1010 ( = 0.9987) and XN = 0.0066 × ψ + 0.1101 ( = 0.9285). This is the first study of UAN and XN decay in BL and the findings add to our understanding of mineralizable N from BL.

Core Ideas Dew deposition is often overlooked in humid regions but may play an important role in nutrient cycling for surface‐applied fertilizers and broiler litter. Dew accumulated during the measurement period accounted for 6% of the precipitation measured with heaviest dew recorded in the spring and winter months. Under laboratory conditions, simulated dew led to increased ammonia loss for surface‐applied broiler litter. Incorporation of dew as a significant weather variable may better aid in predicting NH3 loss using simulation models. Dew deposition is often overlooked in humid regions, such as the southeastern USA, but may play an important role in nutrient cycling for surface‐applied fertilizers and broiler litter. The objectives of this study were to measure dew in a pasture and to evaluate the effect of simulated dew on NH3 volatilization in a laboratory study. A microlysimeter method was used to measure dew in a tall fescue (Festuca arundinacea Schreb.) and bermudagrass (Cynodon dactylon L.) pasture over 206 d. In the 206 d measured, 119 d received dew with an average dew fall of 0.19 mm and greater events observed in the cooler spring and fall months. Dew accumulated during the measurement period accounted for 6% of the precipitation measured. Under lab conditions, the effect of simulated, daily dew (0.2 mm) on NH3 volatilization from surface‐applied broiler litter to air‐dry soil was evaluated under diurnal fluctuations of temperature (6–27°C) and relative humidity (26–91%) for 15 d. Dew application significantly increased NH3 volatilization losses (31% of the applied NH4–N and 5% of the applied total nitrogen [TN]) when compared with NH3 losses in the absence of dew (15% of the applied NH4–N and 2.4% of the applied TN). These results suggest that dew may affect NH3 losses from surface‐applied broiler litter under dry field conditions.

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The pH value of poultry litter is affected by nitrification, mineralization, and the addition of acidifying chemicals, all acting on the poultry litter pH buffering capacity (pHBC). Increased understanding of poultry litter pHBC will aid in modeling NH volatilization from surface-applied poultry litter as well as estimating rates of alum applications. Our objectives were to (i) determine the pHBC of a wide range of poultry litters; (ii) assess the accuracy of near-infrared reflectance spectroscopy (NIRS) for determining poultry litter pHBC; and (iii) demonstrate the use of poultry litter pHBC to increase the accuracy of alum additions. Litter pHBC was determined by titration and calculated from linear and sigmoidal curves. For the 37 litters measured, linear pHBC ranged from 187 to 537 mmol (pH unit) kg dry litter. The linear and sigmoidal curves provided accurate predictions of pHBC, with most > 0.90. Results from NIRS analysis showed that the linear pHBC expressed on an "as is" water content basis had a NIRS coefficient of calibration (developed using a modified partial least squares procedure) of 0.90 for the 37 poultry litters measured. Using the litter pHBC, an empirical model was derived to determine the amount of alum needed to create a target pH. The model performed well in the range of pH 6.5 to 7.5 (RMSE = 0.07) but underpredicted the amount of alum needed to reach pH <6. The lack of model performance at pH <6 was probably due to Al reacting with organic matter in the poultry litter, which prevented its hydrolysis.