Crabgrass (Digitaria spp.) is deemed as a productive and nutritious warm-season annual forage for livestock in the U.S. transition zone. However, there is limited information about nitrogen (N) source and rate effects on productivity and nutritive value of crabgrass in North Carolina. Herbage accumulation (HA), N removal, crude protein (CP), total digestible nutrients (TDN), and tissue nitrate (NO₃⁻) concentrations were evaluated for 2 yr (2020 and 2021) in two physiographic regions (Piedmont and Coastal Plain). Treatments were five rates of chemical N fertilizer (up to 480 kg N ha⁻¹), five rates of plant-available N from broiler poultry litter (up to 472 and 399 kg N ha⁻¹ in 2020 and 2021, respectively), and one control (zero N). Overall crabgrass responses were not different between N sources. At Coastal Plain, HA increased from 4,990 kg dry matter (DM) ha⁻¹ and plateaued at 7,136 kg DM ha⁻¹ at an agronomic optimum N rate (AONR) of 198 (SE = 49) kg N ha⁻¹. At Piedmont, HA responses were erratic, estimation of an AONR was not possible, and HA values were approximately half or less to those at Coastal Plain. Removal of N was linearly associated with HA. Increasing N rate had a marginal positive effect on CP (ranged from 126 to 154 g kg⁻¹) and no effect on TDN (averaged 626 g kg⁻¹). Tissue NO₃⁻ values were below the toxic threshold for feeding livestock. Poultry litter is an effective N source for crabgrass. Nitrogen rate effects were more apparent on crabgrass’ productivity; nutritive value was generally high regardless of N rate and source.

中文翻译：

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家禽垫料和氮肥对马唐生产力和营养价值的影响

马唐 ( Digitaria spp.) 被认为是美国过渡区牲畜的高产且营养丰富的暖季年度草料。然而，关于北卡罗来纳州马唐生产力和营养价值的氮 (N) 来源和速率影响的信息有限。在两个地貌区域（皮埃蒙特和平原和沿海平原）评估了 2 年（2020 年和 2021 年）的牧草积累 (HA)、氮去除、粗蛋白 (CP)、总可消化营养素 (TDN) 和组织硝酸盐 (NO ₃ ^- ) 浓度). 处理包括五种比例的化学氮肥（高达 480 kg N ha ^-1），五种来自肉鸡垫料的植物可利用氮（高达 472 和 399 kg N ha ^-1分别在 2020 年和 2021 年）和一个对照（零 N）。马唐的整体反应在 N 来源之间没有差异。^{在沿海平原，在 198 (SE = 49) kg N ha -1}的农学最佳施氮量 (AONR) 下，HA 从 4,990 kg 干物质 (DM) ha ^-1增加到 7,136 kg DM ha ^-1。在皮埃蒙特，HA 反应不稳定，无法估计 AONR，并且 HA 值大约是沿海平原的一半或更少。N 的去除与 HA 呈线性相关。增加 N 速率对 CP 有边际积极影响（范围从 126 到 154 g kg ^-1），对 TDN 没有影响（平均 626 g kg ^-1）。组织 NO ₃ ^-值低于饲养牲畜的毒性阈值。家禽垫料是马唐的有效氮源。施氮量对马唐生产力的影响更为明显；无论施氮量和来源如何，营养价值普遍较高。