Nitrogen (N) requirements for switchgrass (Panicum virgatum L.) forage production in the Mid-south are largely unknown. This study determined switchgrass forage yield, quality, N removal, and soil fertility response in a two-forage harvest (pre-anthesis) system after split applications of 0, 84, 168, 252, and 336 kg N ha -1 yr -1 from 2014 to 2016. Controls were represented by no fertilizer and a 0 N rate with supplemental P, K, Mg, and S. For all experimental years, yield did not benefit from supplemental P, K, Mg, and S, suggesting N was the limiting nutrient. Yield also did not differ between the 252 and the 336 kg N ha -1 yr -1 rates (9.2 and 9.4 Mg ha -1 , respectively), indicating no further growth beyond the 252 kg N ha -1 threshold in a two-cut forage system. At greater N fertility rates (336 kg N ha -1 ), the majority of the soil nutrient concentrations were reduced compared with the 252 kg N ha -1 rate, owing to greater nutrient removal in harvested plant tissue. Tissue N removal was greatest for the highest N application, albeit not different from the 252 kg N ha -1 rate; N use efficiency had an inverse relationship with N removal, peaking during the lowest N application (84 kg N ha -1 ). Forage quality varied, but, in general, digestibility improved under greater N fertility. Quantifying trends in forage yield and quality based on N fertility are useful for predicting break-even prices per fertilizer response.Abbreviations: ADF, acid detergent fiber; CP, crude protein; NDF, neutral detergent fiber; NUE, nutrient use efficiency; TDN, total digestible nutrients.This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.

Core Ideas Recommended P and K rates are largely unknown for native grasslands. Switchgrass requires low levels of P and K in a two‐cut forage system. There are limited forage quality gains from P and K fertilizers. Nitrogen is a more limiting nutrient in switchgrass forage systems on marginal soils. Finite nutrients, including P and K, are required in large quantities for many warm‐season forages. However, native perennial grasses such as switchgrass (Panicum virgatum L.) have less of an affinity for fertilizers, although recommended P and K rates are largely unknown. Objectives were to test switchgrass forage yield response to P and K rates representative of warm‐season forages and identify compositional impacts for developing switchgrass forage fertilizer recommendations. Switchgrass cv. Alamo was subjected to two harvests per year after applications of 0, 28, 56, 112, and 224 kg P ha−1, and split applications of 0, 134, 269, 404, and 538 kg K ha−1 yr−1, from 2014 to 2016. Two sets of controls were used, a “nutrient control” (0 P and K with supplemental rates of N and S) and a “control” (no fertilizer). Harvest timing (first or second cuts) did not influence (P ≥ 0.05) P or K removal or forage yields. For all study years, the control (no supplemental fertilizer) resulted in substantially lower (P ≤ 0.05) yields than the nutrient control, meaning yield did benefit (44 and 49% increases) from supplemental nutrient applications. Therefore, minimal P and K inputs are required for a yield response, as there were very few detectable yield increases beyond the lowest tested application rates (134 kg K ha−1 and 28 kg P ha−1). Results indicate P and K are required in low amounts and that N is a more limiting nutrient in switchgrass forage systems on marginal soils of the southeast.

Agronomic management practices that maximize monoculture switchgrass (Panicum virgatum L.) yield are generally well understood; however, little is known about corresponding effects of differing switchgrass management practices on near-surface soil properties and processes. The objective of the study was to evaluate the effects of cultivar ("Alamo" and "Cave-in-Rock"), harvest frequency (1-and 2-cuts per year), fertilizer source (poultry litter and commercial fertilizer), and irrigation management (irrigated and non-irrigated) on near-surface soil properties and surface infiltration in a Leadvale silt loam (fine-silty, siliceous, semiactive, thermic, Typic Fragiudult) after four years (2008 through 2011) of consistent management in west-central Arkansas. Irrigating switchgrass increased (P < 0.01) soil bulk density in treatment combinations where poultry litter was applied (1.40 g•cm −3) compared to non-irrigated treatment combinations (1.33 g•cm −3). Root density was greater (P = 0.031) in irrigated (2.62 kg•cm −3) than in non-irrigated (1.65 kg•cm −3) treatments when averaged over all other treatment factors. The total infiltration rate under unsaturated conditions was greater (P = 0.01) in the 1-cut (33 mm•min −1) than 2-cut (23 mm•min −1) harvest treatment combinations when averaged over all other treatment factors, while the total infiltration rate under saturated conditions did not differ among treatment combinations (P > 0.05) and averaged 0.79 mm•min −1. Results from this study indicate that management decisions to maximize switchgrass biomass production affect soil properties over relatively short periods of time, and further research is needed to develop local best management practices to maximize yield while maintaining or improving soil quality. A. Jacobs et al.

American sycamore (Platanus occidentalis L.) was planted on bottomland and terrace sites in the Ohio River Valley region of western Kentucky to test the effects of various cultural treatments on yields over short rotation periods. Without fertilization, the bottomland site was more productive, but yields from the fertilized plots on the two sites were comparable. Fertilization significantly increased yields of all biomass components; the NP treatment did not increase yields over the N treatment. Yields of bolewood and bark were significantly increased by closer spacings. Average annual production, exclusive of leaves, for the most productive treatment combination (6 x 3 ft. spacing and N fertilization after five years on the terrace) was approximately 6 tons/acre/year on a green-weight basis. Without fertilization, the 1 x 3 ft. spacing was most productive, yielding nearly 4 tons/acre/year after either the three- or four-year rotation period on the bottom site.