This work examines N use by switchgrass (Panicum virgatum L.). A study was conducted on two well-established 'Cave-in-Rock' switchgrass stands in Blacksburg (37°11′ N, 80°25′ W) and Orange (38°13′ N, 78°07′ W) Virginia, USA. Plots were fertilized in 2001 (year 1) with 0, 90, 180, or 270 kg N per hectare. No additional N was applied in 2002 (year 2) and 2003 (year 3), and biomass was harvested in July and November for years 2 and 3 (but only in November of year 1). Root and soil samples were collected in May, July, September, and November each year and analyzed for N. Nitrogen fertilization did not increase yields in 2001 (year 1), but it did provide residual benefits in 2002 (year 2) and 2003 (year 3).Root-N levels at 15 cm depth increased with fertilization, fluctuated seasonally between roots and shoots, and root-N was reduced over the course of the study. With two harvests per year, about 100 kg N hectare per year were removed in biomass, even in plots with no N added-suggesting N already present in the soils (at 15 cm depth) contributed to yields; but the soil mineral-N pools were reduced by the end of year 3. Nitrogen-use efficiency, apparent N recovery, and partial factor productivity were reduced with higher N applications. The data support the notion that biomass production can be achieved with minimal N inputs, but stands must be managed to maintain that N reserve over the long term. There is also a need to quantify the N pool to depths greater than 15 cm in other agro-ecoregions.

Located within the Sahel region, Senegal faces several agricultural production challenges. Limited rainfall, poor soil fertility, and insuffi cient agronomic inputs all contribute to low pearl millet [Pennisetum glaucum (L.) R. Br.] yields. Th is study was initiated to assess the potential for increasing millet yields through intercropping (living cover) and mulching (desiccated cover) practices. During the 2013 and 2014 growing seasons, pearl millet was intercropped with cowpea [Vigna unguiculata (L.) Walp.], mungbean [Vigna radiata (L.) Wilczek], or grown under mulch (neem [Azadirachta indica] leaves applied at 2 t ha-1). Field trials were conducted at two sites within Senegal's central milletpeanut (Arachis hypogaea L.) basin, in Bambey (14°41¢38² N, 16°28¢12² W) and Th iés (14°45¢45² N, 16°53¢14² W). Soil moisture and plant N (based on the normalized diff erence vegetation index [NDVI]) were measured in addition to yield. When intercropped with a legume, millet grain yields increased up to 55% compared to millet alone. Th e combined grain yields under intercropping (millet + legume) were always higher than yields of millet alone, up to 67% in Bambey. Mulching increased soil moisture up to 14%, with yield increases of up to 70% over millet with no mulch. Plant N increased in both intercropped and mulched millet, with NDVI increases up to 21% with mulch and 16% when grown with a legume (prior to fl owering). Th ese yield increases were achieved using resources that are available and aff ordable to small-scale producers in the region (seeds and mulch), and did not require the addition of fertilizer inputs.

Ensuring food and nutritional security in light of high climate variability and a rapidly growing population remains a challenge. Mungbean (Vigna radiata (L.) Wilczek) is a short duration, drought-tolerant, and ureide-exporting legume crop capable of symbiotic atmospheric nitrogen fixation. Estimates of biological N 2 fixation by mungbean in different soil textures have not been extensively studied. We conducted this study to evaluate plant growth and N 2 fixation of five mungbean genotypes (Berken, 8735, IC 8972-1, STB#122, 223) inoculated with Bradyrhizobium spp. and grown on loamy sand and silt loam soils under glasshouse conditions. Mungbean dry matter yield, δ 15 N values, shoot content, amounts of N-fixed, and soil N uptake were all higher on the silt loam soil compared to the loamy sand soil, demonstrating the effects of soil properties on plant growth and N 2 fixation potential. Among genotypes, IC 8972-1 produced the highest biomass (7.85 g plant −1), shoot N content (200 mg plant −1), and soil N uptake (155 mg plant −1) than other genotypes. The significant interaction between soil texture and genotypes for root dry matter and %Ndfa indicates the major role of legume root-nodule bacteria in symbiotic N 2 fixation. This study demonstrated that N 2 fixation in mungbean is affected by both genotypes and soil properties, illustrating the need to consider soil properties in order to maximize N contribution from mungbean to agricultural production systems.

Tall fescue [Schedonorus phoenix (Scop.) Holub] is a widely used and important cool‐season forage grass in the eastern United States. Reduced forage production during hot, dry, mid‐ to late‐summer periods and animal toxicities associated with the presence of a fungal‐endophtye limit the utility of tall fescue for some producers. We investigated interseeding teff [Eragrostis tef (Zucc.) Trotter], a warm‐season annual grass, into established fescue stands as a means to improve summer forage production and potentially reduce fescue toxicities. Teff established rapidly regardless of seeding method (broadcast or no‐till) or seed‐coating treatment (with or without a commercial polymer coating), but its abundance varied from year to year. Teff contribution to the swards was twice as great in the warmer season of 2010 (40%) than in the cooler seasons of 2008 and 2009. Significant contributions from teff were associated with greater dry matter yields, lower protein, and higher fiber contents relative to the non‐interseeded control plots. Reduced forage quality may be related to rapid reproductive development of teff when other species were vegetative and the high fiber content of warm‐season species. Overseeding teff may benefit producers by reducing relative fescue content and increasing dry matter production of fescue‐dominated swards during hot summer periods.

Pearl millet [Pennisetum glaucum (L.) R. Br.] yields in Senegal are constrained by rainfall variability, persistent drought, and low soil fertility. Mungbean [Vigna radiata (L.) Wilczek], a short-duration and relatively drought-tolerant legume crop, is capable of improving soil fertility and productivity of associated crops. Our study evaluated the effects of pearl millet and mungbean intercropping on crop yields in the semi-arid regions of Senegal. Field experiments were conducted during the 2017 and 2018 growing seasons at Bambey and Nioro sites located within Senegal's west-central and Saloum agricultural regions, respectively. Experimental treatments: monocropped millet (T 1), monocropped mungbean (T 2 , 100%), and 23% (T 3), 43% (T 4), 47% (T 5), 62% (T 6), 125% (T 7), and 164% (T 8) of mungbean intercropped with millet were laid out in a randomized complete block design and replicated four times. In addition to yield, canopy cover and normalized difference vegetation index (NDVI) were measured and yield advantage was assessed with the land equivalent ratio (LER). Combined millet and mungbean seed yields were up to 60 and 85% higher under intercropping systems compared to millet monocropping at Bambey and Nioro, respectively. Similarly, LER was always greater than unity (> 1) under millet-mungbean intercropping compared to millet monocropping. Mean canopy cover estimates and NDVI values increased by up to 60 and 30% in millet-mungbean intercropping over millet grown alone, respectively. These combined yield gains obtained without fertilizer applications suggested that optimizing mungbean density (62-125%) in pearl millet-based systems can increase the combined yields in a low-input and/or high-risk environment in Senegal.