Context: Warm-season legume cover crops in subtropical environments provide many agroecosystem services but have not been widely adopted because their use usually entails replacing cash crops. Planting short-term legume cover crops following maize (Zea mays L.) to replenish soil nitrogen (N) pools for cool-season cash crops, such as wheat (Triticum aestivum L.), is an innovative approach for integrating legumes into subtropical cereal cropping systems that has not been widely investigated. Objectives: A maize-legume cover crop-wheat cropping sequence under conservation tillage management was investigated with the following objectives: 1. Evaluate the performance of short-term cowpea [Vigna unguiculata (L.) Walp)] and sunn hemp (Crotalaria juncea L.) cover crops in terms of N accumulation, 2. Track soil N availability and wheat N recovery following cover crops, and 3. Assess wheat productivity in response to cover crops terminated and left on the soil surface. Methods: A five site-year study was conducted in Citra and Jay, Florida, USA beginning in 2016. The experiment was arranged as a split-plot in which cover crop (cowpea, sunn hemp, and weed-free fallow) was the main plot factor, while N rate (0, 34, 67, and 101 kg N ha-1) to wheat was the split plot factor. Corn was planted under strip-tillage, while cover crops and wheat were planted into residues using a no-till grain drill. Results: Cover crops accumulated 58-126 kg N ha-1 in eight to 11 weeks, with cowpea and sunn hemp deriving up to 67 and 90% of N from biological N fixation, respectively. Plant Root Simulator probes and Normalized Difference Vegetation Index data provided evidence for higher N uptake by wheat following cover crops compared to weed-free fallow during early stages of wheat growth. However, N availability following cover crops was either short-lived or insufficient as wheat stover production, grain yields, and grain N recovery were not affected by cover crops in most cases. On the few occasions when positive cover crop effects were detected, results were both marginal and inconsistent. Conclusions: Maintaining cowpea and sunn hemp residues on the soil surface may be beneficial from a soil conservation perspective, but this strategy does not result in consistent improvements in the productivity of cool-season cereals. Additional research that elucidates the environmental pathways by which legume cover crop-derived N is lost from soil is warranted to facilitate the development of management practices that increase the likelihood and size of N benefits from short-term legumes.

Water use is the greatest challenge facing the turfgrass industry. Breeding for drought responses is complicated by variable environmental factors, and it can be difficult to determine if selections are based on drought avoidance or drought tolerance mechanisms. The use of polyethylene glycol (PEG) offers potential for development of an efficient screening method for drought tolerance. A preliminary study was conducted to assess different rates of PEG 6000 equilibrated with known osmotic potentials of sucrose to evaluate the turfgrass quality, leaf wilting/firing, and rooting of FAES1305 zoysiagrass. A second study was subsequently conducted using 23% PEG 6000 to screen genotypes of zoysiagrass for their drought responses. Sucrose was unsuitable due to rapid induction of drought stress symptoms. Over the course of a 10‐day period, the PEG solutions produced observable changes in turfgrass quality and leaf wilting/firing of FAES1305 zoysiagrass compared to its growth without PEG, thus indicating the potential for use of PEG as a screen for drought tolerance in zoysiagrass. Among nine zoysiagrasses evaluated in the second study, SS‐500 (Empire ® ), Zeon, and FZ1252 consistently showed earlier and greater signs of drought stress compared to FAES1319 (Brazos ® ) and Palisades. The use of PEG 6000 at the concentrations studied is useful to screen multiple genotypes of zoysiagrass for drought responses.

Periodic drought and shortage of potable water have led many municipalities in Florida to set limitations and restrictions on irrigation frequency for home lawns. These restrictions do not take into account turfgrass health and response and may be inappropriate across different species and cultivars; hence, there is a need to identify genotypes that could sustain quality and performance under reduced irrigation. A study was conducted at the University of Florida Plant Science Research and Education Unit in Citra, FL, to assess turfgrass response of 10 bermudagrass ( Cynodon spp.), nine zoysiagrass ( Zoysia spp.), and five seashore paspalum ( Paspalum vaginatum Swartz) cultivars to different irrigation regimes, consisting of non-irrigated control (Rainfed), soil moisture sensor (SENSOR)-based (up to 152 mm mo −1 ) , 8X per month (8XMO up to 152 mm mo −1 ), 4X per month (4XMO up to 76 mm mo −1 ), 2X per month (2XMO up to 38 mm mo −1 ), and 1X per month (1XMO up to 19 mm mo −1 ). Plots were evaluated for turfgrass quality and percent green cover using digital image analysis every 3 days over a 22-month period. Bermudagrass was able to sustain acceptable turfgrass quality during one of the growing seasons when irrigated 4XMO, showing substantial water savings compared to the other two species. SENSOR irrigation significantly reduced water consumption for all the three species and produced turfgrass quality similar to 8XMO irrigation. Results indicate that selecting the right cultivar for the area could help sustain turfgrass aesthetic and functionality.

Soil water repellency inhibits seed germination and emergence, whereas soil surfactants improve the wettability of water-repellent or hydrophobic soils. An improvement in seed germination and emergence can occur when a soil surfactant is applied directly to the seed and/or to the water repellent soil at sowing. Therefore, a coating process was developed to utilize seed as a soil surfactant carrier. Greenhouse experiments were conducted to evaluate establishment of perennial ryegrass (Lolium perenne L.) seed coated with a soil surfactant (SCS = surfactant- coated seed), as compared to uncoated seed (CHK). Both SCS and CHK were sown in two hydrophilic substrates (100% sand [WSAND], 90:10% v/v sand:peat [WSP], and in two severely hydrophobic sands (100% hydrophobic stearic acid-treated sand [HSS], and hydrophobic 90:10% v/v sand:peat [HSP]). Due to the weight of the coating, SCS was sown at half the amount as compared to CHK; however, final turfgrass establishment in all rootzones with SCS was similar or better than CHK. In WSAND, WSP, and HSP, the volumetric water content was consistently higher in rootzones of SCS treatments versus CHK. SCS represents an opportunity to improve stand establishment and rootzone soil-water dynamics in challenging environmental conditions such as limited precipitation. Species used in this study: Perennial ryegrass, Lolium perenne L.

Methods to evaluate soil water repellency (SWR) require extensive studies on field soils and are subject to the heterogeneity of SWR throughout the soil profile as well as plant/soil interactions. The objectives of this study were to develop a synthetic method to create hydrophobic sand, and to determine if that hydrophobic sand would affect the establishment of bermudagrass ( Cynodon dactylon L. Pers. × C. transvaalensis Burtt-Davy, cv. Tifeagle) sprigs. Two techniques were developed to render sand hydrophobic: soap:sand method (hydrophobic sand; HSS) and sand:peat method (hydrophobic sand and read sedge peat; HSP). Both HSS and HSP remained severely hydrophobic at 0 cm depth for only 7 d, and at the 1- to 6-cm depth for 77 continuous days, as determined by water drop penetration time. Bermudagrass establishment, root growth, or shoot growth in two greenhouse experiments with four root zone substrates–HSS, HSP, WSAND (wettable sand), and WSP (wettable sand and reed sedge peat)—were not consistent. In conclusion, both HSS and HSP were shown to be safe and effective methods to synthetically produce hydrophobic sand for potential use in laboratory research, but further evaluation is needed to determine the feasibility of using HSS and HSP for turfgrass growth evaluations.

There is a gap in our understanding of grain sorghum [Sorghum bicolor (L.) Moench] crop production and soil resource (water and N) use in response to different crown root angles (CRA) in any pedoclimatic conditions. CRA is used as a proxy for different root system architectures in field conditions. Therefore, we selected grain sorghum genotypes previously classified to exhibit 'shallow' (measured angle 40.5) and 'steep' (measured angle 59.3) CRA from a diverse panel of 130 recombinant inbred lines to evaluate aboveground responses to CRA under different agronomic practices. These lines were planted as architectural monocultures and compared with a rooting architecture diversity treatment ('shallow', 'intermediate' (measured angle 47.4), 'steep') at four N rates (0, 20, 100, and 200 kg N ha(-1)) for two years in Experiment I. Similarly, the monocultures 'shallow' and 'steep' were compared to two rooting architecture di-versity treatments ('mix2 ' and 'mix10 ') under two water regimes (irrigated vs. rainfed) for two years in Exper-iment II. Yield, other aboveground plant traits, soil water and N dynamics were evaluated. In Experiment I, increasing N application rate positively influenced all the aboveground traits measured, while rooting archi-tecture had minimal or no impact on crop N uptake and other parameters. There were no yield benefits or penalties associated with different CRA. The results of Experiment II indicated that, while root system archi-tecture did influence a variety of soil response variables, including water drainage and NO3-N leaching below the rootzone, the trends across CRA treatments and years made the results largely inconclusive. Few studies have been conducted on this topic, some showing positive outcomes, but results of these studies showed limited benefit of diverse and contrasting CRA to sorghum productivity, N recovery, and water uptake when grown in coarse-textured soil.

Growing urban populations have placed greater demands on municipal water supplies, especially during dry periods. Efforts are underway to develop turfgrasses with better performance using less irrigation. The objective of this research was to assess the effects of irrigation management and St. Augustinegrass [ Stenotaphrum secundatum (Walter) Kuntze] genotype on turf quality (TQ). The field study conducted in Citra, FL, was a split-plot design with the main plot (irrigation) arranged in blocks. Calendar-based irrigation treatments were soil sensor-based, 8X, 4X, 2X, and 1X per month (MO) and none. St. Augustinegrass genotypes included three commercial cultivars and eight experimental entries. Turfgrass quality varied with time, genotype, and irrigation. Sensor-based and 8XMO irrigation produced the highest TQ values, ranging from 5 to 7 for all cultivars, but sensor-based irrigation used less water overall. Turf quality declined with 2XMO and more restrictive irrigation frequencies, with TQ values ranging from 2 to 4. Several recently developed breeding lines performed better across all the irrigation treatments than current commercial cultivars. To satisfy both municipal watering restrictions and turfgrass health requirements, sensor-based irrigation coupled with the use of improved breeding lines and cultivars such as DALSA 1618 or FSA1602 (CitraBlue ® ) offer the potential to maintain quality turfgrass while substantially reducing residential irrigation use.

Salinization is a great threat to wetlands and freshwater ecosystems. Increased salinity can disturb native aquatic vegetation and provide an empty niche for invasion of non-native species. To understand the fate of aquatic flora under increased salinity levels, 14 dominant wetland species with different growth forms (submersed, amphibious, floating-leaved, emergent and woody/tree) were exposed to increased salinity conditions. The objective was to assess the salt tolerance threshold for each species and model their performance in response to a salinity gradient ranging from 0.2 to 20 parts per thousand (ppt). Plant growth and survival rate were analyzed using a nonlinear regression model to project sublethal salinity concentrations that would reduce biomass and visual quality of each species by 50% (LC50). Results showed that a few non-native species (alligatorweed: Alternanthera philoxeroides (Mart.) Griseb., torpedograss: Panicum repens L., and Brazilian peppertree: Schinus terebinthifolius Raddi) survived 20 ppt salinity, whereas all other native and non-native species perished at salinity below 10 ppt. Increased salinity can suppress salt-sensitive native plants and increase the opportunity of invasion for salt-tolerant non-native species. This suggests that alligatorweed, torpedograss and Brazilian peppertree pose a more significant threat to the ecosystem if salinity levels continue to increase in freshwater ecosystems and exacerbate the encroachment of non-native species into native plant communities.

Increasing urban growth has placed a strain on limited potable water resources. Therefore, improved drought tolerance in turfgrass is important to reduce the need for supplemental irrigation to maintain the aesthetic value and functionality of turfgrass areas. Field evaluations are subject to variability in irrigation patterns, wind, soil, and drainage patterns within an experimental area. The objectives were to evaluate the effect of polyethylene glycol (PEG) on root and shoot production in species of Zoysia and determine if PEG is suitable for screening genotypes for drought responses. Two experiments were conducted, each arranged as a randomized complete block design. Experiments used plants grown in conetainers with and without PEG in hydroponic culture. Plants were evaluated for root length density, root surface area, root diameter, leaf mass, leaf wilting, and turfgrass quality. The PEG treatment produced minimal differences. The results indicated that higher PEG concentrations are needed to elucidate drought responses and observe differential drought responses among zoysiagrasses.

While improved crop water-deficit tolerance is considered of primary importance, many phenotyping efforts focusing on quantifying structural root traits make assumptions about architecture representing root function. Therefore, the aim of this study was to quantify whole plant water-use traits among disparate peanut (Arachis hypogaea L.) genotypes and determine their impact on water-deficit tolerance. Mini-rhizotrons were installed to evaluate genotypic root architecture and developmental changes to two irrigation regimes imposed during early development. Following the early-season irrigation regimes, above- and below-ground traits were studied across a range of soil water conditions through measures of: (a) leaf-level gas exchange and (b) soil water depletion quantified using a novel soil water probe inserted into mini-rhizotrons allowing for matched root architecture and soil water depletion measures. While differential water treatments influenced root system architecture development among the genotypes, soil water depletion locations were primarily determined by water availability in the soil profile, not simply by having greater root length at a given soil location. This contradicts the assumption that greater root presence is a consistent indicator of increased root activity. Phenotypic selection of root traits for improving the efficiency of crop water use should consider both structural and functional traits in relation to the intended production environments slated for future cultivar development.

Improper nutrient management strategies often results in soil N and P imbalances, which can lead to unintended environmental consequences. Nutrient budgets can be useful tools to identify nutrient imports and exports and assess the agronomic and environmental performance of different pasture nutrient management options. In this 3-yr study, we used a farm-gate nutrient budgeting approach to determine N and P use efficiency in subtropical perennial pasture systems subjected to different nutrient management strategies. Treatments consisted of repeated application of biosolids and inorganic fertilizer (at an equivalent rate of 160 kg plant available N ha(-1) yr(-1)) either alone or in combination with (20 Mg ha(-1) yr(-1)). Major N and P inputs and outputs were: N and P added via fertilizer and biochar, plant uptake, leaching, and denitrification (N budget only). Nitrogen recovery in forage above-ground biomass accounted for a significant proportion of applied N (similar to 64%) and P (22%). Greater N leaching occurred in inorganic fertilizer (29% of applied N) vs. biosolids treatments (average of 7% of applied N). Negligible P leaching (0.1-0.2% of total P applied) occurred, regardless of the treatment. Biochar did not affect either crop N and P use efficiency or P leaching, but reduced N leaching for treatments receiving inorganic fertilizer. Treatments showed no impact on soil N, but vertical distribution of soil total P changed over 3 yr, suggesting downward movement of P. Despite the high initial soil test P levels, biosolids application at P loads exceeding agronomic recommendations improved agronomic N and P efficiency relative to control treatments with no impact on N or P leaching.

AbstractDrought is the greatest abiotic cause of soybean [Glycine max (L.) Merr.] yield loss in rainfed systems in the United States. Preplant incorporation of powdery biochar to soil cultivated with soybean in these water‐stressed regions presents the potential to increase volumetric soil water content (VSWC) between rainfall events and ameliorate the impact of intermittent water stress. However, VSWC and the above‐ and belowground response of soybean to biochar amendment are not well understood. This 2‐yr field study (2014–2015) evaluated the effectiveness of incorporating powdery (325 μm) biochar to 0.2‐m soil depth to increase soil water storage in a coarse‐textured soil in the southeastern United States. Soybean yield, aboveground biomass accumulation, root morphology, and VSWC in the soil profile to 1‐m depth were assessed under three biochar rates (0, 2.5, and 10 Mg ha–1) and two water treatments (rainfed and irrigated). In 2014, application of 10 Mg biochar ha–1 increased the cumulative soil water storage in the top 1‐m soil depth. Biochar application did not affect soybean yield or root morphology. Biochar only elicited changes in fresh weight of pods during reproductive stages, which indicates biochar's limited benefit to the water status of this shoot component. Irrigation increased yield by 28% compared with the rainfed treatment. Our study provides evidence that field application of biochar to soybean may be a sustainable practice to sequester recalcitrant C in the soil when biochar is available to producers, but its benefits on protecting soybean yield from water stress might depend on other factors such as soil texture, rainfall amount, and frequency.

Salinity is a major abiotic stress that adversely affects plant growth and development. Canola (Brassica napus L.) is an important oilseed crop in the world, and its yield decreases drastically with increasing salinity. To date, little is known about the molecular mechanisms underlying its salt stress response and tolerance. This study combines physiological assays with comparative proteomics to understand how B. napus plants respond to salt stress. The changes in relative water content, electrical conductance, stomata conductance, intercellular CO2 concentration, transpiration rate, photosynthesis rate, water usage efficiency, respiration rate, chlorophyll fluorescence, antioxidant enzyme activities, soluble sugar, proline and betaine in B. napus plants under different NaCl concentrations were analyzed. Proteomic profiles of B. napus plants under 100, 200 and 400 mM NaCl treatment at 7 day and 14 day were acquired using iTRAQ LC-MS/MS based quantitative proteomics. A total of 2316 proteins were identified in B. napus leaves, of which 614 proteins showed differential expression under salt stress. These proteins were mainly involved in 10 processes, of which proteins in stress and defense, metabolism and photosynthesis pathways ranked the top three. Subcellular localization analysis showed that most proteins were located in chloroplast, cytoplasm, mitochondria and nucleus. A total of 138 differentially expressed proteins were predicted to interact with each other. These results have provided a comprehensive view of the physiological and molecular processes taken place in B. napus leaves under salt stress, and revealed the molecular mechanisms underlying salt tolerance of B. napus plants.

The genetic uniformity of monocultures extends belowground to the genetic controls over the architectural configuration of the root system. We hypothesized this may encourage inefficiency in resource acquisition compared with crops with diversity in root system architecture among plants. Here, we report on an evaluation of root systems in grain sorghum [Sorghum bicolor (L.) Moench] populations phenotyped by crown root angle as "shallow" and "steep" rooted, and diverse mixtures (shallow, intermediate, and steep), at four N rates (0, 20, 100, and 200 kg N ha(-1)) in a sandy soil with a plow layer. Differences in the spatial distribution of root mass among architecturally contrasting populations were confirmed by direct measures in the field, which has not been previously reported in sorghum. This confirmation, plus confirmation of differences in root N distribution with soil depth, indicate that soil C and N dynamics would differ among sorghum populations differing in root system architecture. Patterns in root length density (RLD) by N rate indicated N-based limitation on root proliferation at low N levels and a N-induced suppression of proliferation at high N levels. There was no strong evidence that diverse architectural mixtures would result in tangible improvements in resource acquisition, as they generally had intermediate root mass and did not differ in RLD relative to architecturally contrasting monocultures. The similarity of RLD across rooting architectural types was one of several observed indicators of root growth plasticity, which could be a mechanism to alleviate physical constraints of the plants' inherent first-order rooting structure in taking up soil resources.

Although perennial bioenergy crops provide a potential for soil C sequestration, high fertilizer inputs are required to sustain yields. Land application of bioenergy byproducts can be an effective strategy to reduce the use of inorganic fertilizer. This study examined the impacts of elephantgrass [Pennisetum purpureum (L.) Schum.] bioenergy cropping and conventional pasture on soil C and N responses. Treatments included (a) bahiagrass + 50 kg N ha(-1) yr(-1) (BHG), (b) elephantgrass + 50 kg N ha(-1) yr(-1) (E50), (c) elephantgrass + 50 kg N ha(-1) yr(-1) + fermentation residual (E50FR), (d) elephantgrass + 50 kg N ha(-1) yr(-1) + biochar (E50BC), and (e) elephantgrass + 250 kg N ha(-1) yr(-1) (E250). Soil C and N responses occurred mainly at the 0- to 10-cm depth. Biochar resulted in the largest increase in soil C stocks at the 0- to 10-cm depth (5.8 Mg C ha(-1) in 2012 vs. 40 Mg C ha(-1) in 2016), but no differences were observed among the other treatments. Conversely, greater soil N stocks at the 0- to 10-cm depth were associated with the BHG (0.8 and 0.34 Mg N ha(-1) for other treatments). Biochar favored N and C accumulation in the mineral-associated (<53 m) fraction, possibly from the accumulation of fine biochar fragments. In contrast, fermentation residual promoted C accumulation in unprotected light fraction. These results are supported by the delta C-13 signature and C/N ratios of the fractions. Results underscore the value of recycling biochar in bioenergy cropping systems as a means of improving C in coarse-textured soils.

Despite the numerous benefits of biosolids, concerns over nutrient losses restrict the extent to which biosolids can be beneficially reused. We evaluated the effectiveness of biochar in controlling the lability of nutrients in agricultural land. This study was designed to investigate the potential impacts of co-applying biochar with biosolids or inorganic fertilizer on N and P leaching losses. A companion paper focuses on greenhouse gas responses. Nutrients were surface applied as biosolids (aerobically digested Class B) and inorganic fertilizer (ammonium nitrate and triple superphosphate) to an established perennial pasture at equivalent annual rates typical of field practices. Biochar was applied at an annual rate of 20 Mg ha-1 . Leachate N and P were monitored using passive-capillary drainage lysimeters. Results demonstrated significant temporal variability in leachate N and P, with larger pulses generally occurring during periods of high water table levels or after intensive rainfall. Inorganic fertilizer generally resulted in greater leachate N and P losses than biosolids. No differences in leachate N and P losses between biosolids and control were observed. Approximately 1% of applied N was lost via leaching from biosolids treatments vs. 16% for inorganic fertilizer. Regardless of the P source, negligible (0.1-0.2% of applied P), cumulative P leaching occurred during the 3-yr study. Biochar had no effect on P leaching but reduced N leaching from treatments receiving inorganic fertilizer by 60%. Prudent nutrient management is possible even on biosolids-amended Spodosols with high water tables.

Objective: The objective of this study was to evaluate nutritive value and fermentation characteristics of silage made with different plant components of sweet sorghum [Sorghum bicolor (L.) Moench] with or without microbial inoculation. Materials and Methods: The experiments were conducted at Ona, Florida, in 2012 (Exp. 1) and 2013 (Exp. 2). In Exp. 1, treatments were the ensiling of different plant components, whole plant (leaves, stem, and inflorescence; WP), stem (stem only, ST), and bagasse (stem pressed to remove the juice, BAG). In Exp. 2, treatments were distributed in a factorial 3 x 2 arrangement with the same plant component treatments from Exp. 1 with or without microbial inoculant (B500). Results and Discussion: In Exp. 1, BAG had greater (P < 0.04) DM, NDF, and ADF and lesser nonfibrous carbohydrate and TDN concentrations than WP and ST. The WP had greater (P = 0.003) CP and lactic and acetic acids and lower (P = 0.04) pH than BAG. The BAG had greater (P = 0.04) yeast count than WP and ST. In Exp. 2, there were no differences in pH among treatments (P = 0.90); however, WP had greater (P < 0.001) TDN and lactic acid concentrations than BAG, and WP silage treated with inoculant had greater (P < 0.05) CP and nonfibrous carbohydrate concentrations. Implications and Applications: Sweet sorghum BAG had acceptable nutritive value and fermentation characteristics and can be used as forage for ruminants. Microbial inoculants may not improve the fermentation characteristics and nutritive value of sweet sorghum BAG silage.

Land application of biochar reportedly provides many benefits, including reduced risk of nutrient transport, greenhouse gas (GHG) emission mitigation, and increased soil C storage, but additional field validation is needed. We evaluated the effectiveness of biochar in controlling the lability of nutrients in agricultural land. This study was designed to evaluate the impacts of biochar co-applied with various N and P sources on GHG fluxes from a subtropical grassland. Nutrients (inorganic fertilizer and aerobically digested Class B biosolids) were surface applied at a rate of 160 kg plant available N ha-1  yr-1 with or without biochar (applied at 20 Mg ha-1 ). Greenhouse gas (CO2 , CH4 , and N2 O) fluxes were assessed using static chambers and varied significantly, both temporally and with treatments. Greenhouse gas fluxes ranged from 1,247 to 23,160, -0.7 to 42, and -1.4 to 376 mg m-2 d-1 for CO2 , N2 O, and CH4 , respectively. Results of the 3-yr field study demonstrated strong seasonal variability associated with GHG emissions. Nutrient source had no effect on soil CO2 and CH4 emissions, but annual and cumulative (3-yr) N2 O emissions increased with biosolids (8 kg N2 O ha-1  yr-1 ) compared with inorganic fertilizer (5 kg N2 O ha-1  yr-1 ) application. Data suggested that environmental conditions played a more important role on GHG fluxes than nutrient additions. Biochar reduced CO2 emissions modestly (<9%) but had no effects on N2 O and CH4 emissions.

Root morphology and production are important for soil nutrient acquisition and C sequestration, but these traits are poorly understood in the bioenergy crop elephantgrass [Pennisetum purpureum (L.) Schum.]. Our objective was to characterize root traits of elephantgrass receiving different nutrient management practices in comparison with bahiagrass (Paspalum notatum Flugge) pasture grown in the southeastern U.S. Treatments were bahiagrass + 50 kg N ha(-1) (BHG), and elephantgrass receiving either: 50 kg N ha(-1) (E50), 50 kg N ha(-1) + biochar (E50BC), 50 kg N ha(-1) + lignocellulosic fermentation residual (E50FR), or 250 kg N ha(-1) (E250). Roots were sampled annually for 4 yr (2013-2016). Root C and N concentration were measured at termination (2016) of the study. Both crop species exhibited similar root length density (RLD) and root mass density (RMD) across all depths in 2014 and 2015. BHG root diameter was 55% greater than all elephantgrass treatments. By 2016, E50FR increased elephantgrass RLD and RMD in the shallow soil layers (< 0.2 m). Root N content was 15-39% lower for all elephantgrass treatments than BHG in the 0-0.1 m depth, and 22-25% lower for E50 and E50BC in the 0.1- to 0.2-m depth compared with BHG. Additionally, roots C content was 6% higher in the 0-0.1 m compared with the 0.1- to 0.2-m soil depth irrespective of treatment. Application of biochar and lignocellulosic fermentation residual as amendments produced a stimulatory effect on elephantgrass root growth in soil shallow layers, which could affect nutrient and water acquisition.

Agricultural extension services in many peanut (Arachis hypogaea L.)-producing regions recommend that farmers reduce nitrogen (N) fertilization rates, or apply N credits, to crops planted after peanut but do not typically specify how peanut residue management or planting schedules of subsequent crops affect the magnitude of peanut N credits. The objective of this study was to quantify peanut N credits to winter wheat (Triticum aestivum L.) in a conservation tillage cropping system in different subtropical growing environments. A five site-year study was conducted in Florida, USA beginning in 2016. A split-plot experimental design was arranged in which summer crop [peanut, cotton (Gossypium hirsutum L.), and weed-free fallow] was the main plot factor, while N rate (0, 34, 67, and 101 kg N ha(-1)) to winter wheat was the split plot factor. Peanut and cotton were planted under strip-tillage, while winter wheat was drilled into peanut and cotton residues and weed-free fallow plots without tillage. Although peanut residues accumulated 54-93 kg N ha(-1), plant available N at winter wheat planting in the 0-15 cm soil depth range of former peanut plots was only higher than in former cotton or fallow plots for one site-year. A previous peanut crop did not affect winter wheat grain yield, but there were cases of lower grain yield, grain N removal, and agronomic efficiency following cotton relative to peanut depending on site. Nonlinear regression procedures predicted that N rates required to optimize grain yields following peanut would exceed 94 kg N ha(-1), further indicating the absence of detectible peanut N credits in this study. These results suggest that assuming peanut provides N credits to subsequent crops in the southeastern USA is not justified and, if assumed, will reduce the productivity of subsequent crops.