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.