Effect of green manure and supplemental fertility amendments on selected soil quality parameters in an organic potato rotation in Eastern Canada

The effects of green manure, crop sequence and off-farm composts on selected soil quality parameters were assessed in a three-year organic potato (Solanum tuberosum L.) rotation in Eastern Canada. Three crop sequences varying in preceding green manure [red clover (RCl) + RCl, and beans/buckwheat or carrots + oats/peas/vetch mixture (OPV)] as main plots and four fertility treatments applied in the potato phase only [control; inorganic fertilizer; municipal solid waste compost (MSW); composted paper mill biosolid (PMB)] as subplots were compared. In 2008 and 2010, changes in selected soil quality parameters (0–15 cm) were assessed prior to planting of potatoes and at potato tuber initiation stage. Potentially mineralizable nitrogen (N) and the acid phosphatase enzyme activity average values across years were greater following RCl (1.51 abs and 622 kg ha^?1) compared with OPV (1.32 abs and 414 kg ha^?1) at potato planting. Soil NO₃–N average value was greater following RCl compared with OPV (63 vs. 52 kg ha^?1) at tuber initiation. For the other measured parameters, OPV and RCl were similar. The soil organic carbon (C) and particulate organic matter-C were greater under PMB and MSW (31.1 and 7.57 kg ha^?1) compared with fertilizer treatment (27.9 and 6.05 kg ha^?1). The microbial biomass C and microbial biomass quotient were greater under MSW (216 kg ha^?1 and 0.73 %) than PMB and fertilizer (147 kg ha^?1 and 0.50 %) across crop rotations. Annual legume green manures and off-farm composts can be used to satisfy potato N requirement and maintains soil quality in organic potato rotations.     

Influence of cultivars and nitrogen rates on the residual effects of potassium applications to preceding cotton on maize

The long-term residual effects of K application rates and cultivars for preceding cotton (Gossypium hirsutum L.) on subsequent maize (Zea mays L.) and the influence of N rates applied to preceding cotton and to maize on the residual K effects were examined on maize under no-tillage in the United States. Two field experiments were conducted on a no-till Loring silt loam at Jackson, TN during 1995–2008 with N rates (90 and 179 kg ha^?1) × K rates (28, 56, and 84 kg ha^?1) and cotton cultivars (determinate and indeterminate) × K rates (56 and 112 kg ha^?1) as the treatments, respectively, in the preceding cotton seasons. Maize was planted under no-tillage on the preceding cotton experiments without any K application during 2009 through 2011. The residual effects of K rates applied to preceding cotton on soil K levels were significantly influenced by the N rates applied to preceding cotton and to maize when the data were combined from 2008 to 2011. Relative to the standard N management practices of 168 kg N ha^?1 for maize and 90 kg N ha^?1 for preceding cotton, the higher N application rate 269 kg N ha^?1 to maize and 179 kg N ha^?1 to preceding cotton reduced the residual effects of K rates on soil K. However, cultivar for preceding cotton did not affect the residual effects of K fertilizer on soil K fertility, leaf K nutrition, plant growth, or grain yield of subsequent maize on a high K field.     

Finger millet response to nitrogen,phosphorus and potassium in Kenya and Uganda

Finger millet (Eleusine coracana (L.) Gaertn) is an important food crop of semi-arid to sub-humid Africa where little is known of its response to applied nutrients. Yield responses to nitrogen (N), phosphorus (P) and potassium (K) together with a diagnostic treatment (S, Mg, Zn, B) were determined from field research conducted in western Kenya and eastern and central Uganda. Grain yield was not affected by applied nutrients in some sites in Kenya, likely due to other prevailing stresses. Grain yield increased with N application for all sites and years in Uganda by a mean of 127% from the no N treatment (0 N) yield of 1.00 Mg ha^?1. Grain yield increases ranged from 0.76 to 1.40 Mg ha^?1 with 30 kg N ha^?1 applied, with little added increase with >60 kg N ha^?1. The mean economically optimal rate for N in Uganda was 72 and 43 kg N ha^?1 with expected net returns to N of 166 and 279 $ ha^?1 when the N cost to grain value was 3 and 9 kg kg^?1, respectively. Yield was increased with P and K application at two of four production areas of Uganda. Yield was increased by >20% with application of Mg–S–Zn–B in addition to N–P–K for all sites in Uganda with foliar concentrations indicating possible S and B deficiency. There is great profit potential in Uganda, and less for Kenya for N, but not for P and K, application to finger millet. Response to S and B needs further exploration.     

Effects of pig and dairy slurry application on N and P leaching from crop rotations with spring cereals and forage leys

Two crop rotations dominated by spring cereals and grass/clover leys on a clay soil were studied over 2 years with respect to nitrogen (N) and phosphorus (P) leaching associated with pig or dairy slurry application in April, June and October. Leaching losses of total N (TN), total P (TP), nitrate-N and dissolved reactive P (DRP) were determined in separately tile-drained field plots (four replicates). Mean annual DRP leaching after October application of dairy slurry (17 kg P ha^?1) to growing grass/clover was 0.37 kg ha^?1. It was significantly higher than after October application of pig slurry (13 kg ha^?1) following spring cereals (0.16 kg ha^?1) and than in the unfertilised control (0.07 kg P ha^?1). The proportion of DRP in TP in drainage water from the grass/clover crop rotation (35 %) was higher than from the spring cereal rotation (25 %) and the control (14 %). The grass/clover rotation proved to be very robust with respect to N leaching, with mean TN leaching of 10.5 kg ha^?1 year^?1 compared with 19.2 kg ha^?1 year^?1 from the cereal crop rotation. Pig slurry application after cereals in October resulted in TN leaching of 25.7 kg ha^?1 compared with 7.0 kg ha^?1 year^?1 after application to grass/clover in October and 19.1 kg ha^?1 year^?1 after application to spring cereals in April. In conclusion, these results show that crop rotations dominated by forage leys need special attention with respect to DRP leaching and that slurry application should be avoided during wet conditions or combined with methods to increase adsorption of P to soil particles.     

Bean yield and economic response to fertilizer in eastern and southern Africa

Bean (Phaseolus vulgaris L.) is important in sub-Saharan Africa for human dietary protein. Low yields are attributed to biotic and abiotic constraints including inadequate nutrient availability. Research was conducted to determine nutrient response functions for bean production areas of Kenya, Mozambique, Rwanda, Tanzania, and Zambia. Mean trial yields ranged from 0.32 to 2.60 and 1.72 to 2.89 Mg ha^?1 for bush and climbing bean, respectively. Response to N was common except in Kenya and Mozambique. The main effect of P and K increased yield in Rwanda only but P and K effects were inconsistent in Zambia. Mean yield increase with a diagnostic treatment containing Mg–S–Zn–B was 0.41 and 0.58 Mg ha^?1 for bush and climbing bean, respectively, in Rwanda and 0.36 Mg ha^?1 in Tanzania with no effects in other countries. In Rwanda, the economically optimal rates (EOR) of N, P and K were > 20 kg ha^?1, but higher with less costly fertilizer. Variations in EOR for growth type varied with nutrient. The EOR of N in Tanzania and Zambia were generally < 10 kg ha^?1, depending on fertilizer costs, but P and K application had profit potential only in Rwanda. Yield, agronomic efficiency and profit to cost ratio, averaged across nutrients, were 36% less, 54% greater and 96% greater, respectively, with nutrients applied at 50% compared with 100% of EOR. Profit potential for the EOR of N is high when expected yield is > 1.5 Mg ha^?1 but responses to P, K and Mg–S–Zn–B vary with bean production area.     

Fertigation combined with catch crop maximize vegetable yield and minimize N and P surplus

Excessive fertilization is a common agricultural practice that often results in high risk of nitrogen (N) and phosphorus (P) losses in vegetable production in China. To reduce these losses, it is crucial to control residual nutrient levels in the rootzone and maintain crop growth. A 3-year field experiment was therefore conducted to investigate the effects of optimal fertigation (OF), OF combined with summer catch crop (OF-SCC; sweet corn with residue incorporation after harvest) or wheat straw application (OF-WSA; soil amended with wheat straw before cucumber seedling transplanting) on soil nutrients, soil residual N and P levels in the rootzone. The conventional management (flood irrigation with excessive fertilization and bare fallow during the summer period) served as control. The results showed that, although OF reduced irrigation amount, N input and P input by 49, 50 and 53%, respectively, it did not affect N and P uptake and fruit yields, and significantly reduced N and P surplus in the rootzone by 60 and 59%, respectively, when compared to the control. The SCC extracted 72–74 kg N ha^?1 year^?1 and 10–13 kg P ha^?1 year^?1 from soils. In addition, SCC and WSA increased soil soluble organic N in the rootzone but had little influence on N and P surplus. Generally, OF was efficient in reducing soil residual N and P, while SCC could temporarily retarded N leaching and improved nutrient recycling in the rootzone. Our results infer that OF combined with SCC is an efficient method for reducing soil N and P losses.     

Soil mineral nitrogen availability predicted by herbage yield and disease resistance in red clover (<Emphasis Type="Italic">Trifolium pratense</Emphasis>) cropping

Nitrogen (N) is the most limiting nutrient in crop production. Legumes such as red clover can provide N through biofixation, but securing nitrogen in soil for subsequent crop production must also be considered. Variety selection and management in red clover cropping can influence soil mineral nitrogen (SMN) availability. A field trial to investigate this was conducted with six varieties, under one and two cut management, over 2 years. Dry matter (DM) and N yield, Sclerotinia resistance and SMN availability were assessed. Low DM and N yields (1.6–2.4 t DM ha^?1 and 54–83 kg N ha^?1) in the first year of cultivation allowed ~?40 kg N ha^?1 to become available, but high DM and N yields (10.2–14.6 t DM ha^?1 and 405–544 kg N ha^?1) allowed ~?20 kg N ha^?1 to become available. Wetter weather in 2015 caused significantly more SMN losses than 2016 (20 kg N ha^?1 in 2015 and 5 kg N ha^?1 in 2016). The varieties Amos, Maro and Milvus lost significantly more SMN in the winter period, which may have been caused by more severe infection of Sclerotinia (these varieties were 50–80% more severely infected other varieties). Varietal effect was non-significant for winter losses in 2016, where no significant varietal differences in Sclerotinia infection were observed. 1 cut made ~?41 kg N ha^?1 available in the growing season of 2015, whilst 2 cut made significantly less (37 kg N ha^?1). Cutting was non-significant in 2016 but 1 cut was less susceptible to losses in the winter period. Cutting in 2015 did not significantly affect herbage DM and N yields in the first or second cut of 2016.     

Nitrogen balance in dryland agroecosystem in response to tillage,crop rotation,and cultural practice

Accounting of N inputs and outputs and N retention in the soil provides N balance that measures agroecosystem performance and environmental sustainability. Because of the complexity of measurements of some N inputs and outputs, studies on N balance in long-term experiments are scanty. We examined the effect of 8 years of tillage, crop rotation, and cultural practice on N balance based on N inputs and outputs and soil N sequestration rate under dryland cropping systems in the northern Great Plains, USA. Tillage systems were no-tillage (NT) and conventional tillage (CT) and crop rotations were continuous spring wheat (Triticum aestivum L.) (CW), spring wheat–pea (Pisum sativum L.) (W–P), spring wheat–barley (Hordeum vulgaris L.) hay–pea (W–B–P), and spring wheat–barley hay–corn (Zea mays L.)–pea (W–B–C–P). Cultural practices were traditional (conventional seed rates and plant spacing, conventional planting date, broadcast N fertilization, and reduced stubble height) and improved (variable seed rates and plant spacing, delayed planting, banded N fertilization, and increased stubble height). Total N input due to N fertilization, pea N fixation, atmospheric N deposition, crop seed N, and nonsymbiotic N fixation was greater with W–B–C–P than CW, regardless of tillage and cultural practices. Total N output due to aboveground biomass N removal and N losses due to denitrification, volatilization, plant senescence, N leaching, gaseous N (NO_x) emissions, and surface runoff were not different among treatments. Nitrogen sequestration rate at 0–20 cm from 2004 to 2011 varied from 29 kg N ha^?1 year^?1 in CT with W–P to 89 kg N ha^?1 year^?1 in NT with W–P. Nitrogen balance varied from ? 39 kg N ha^?1 year^?1 in NT with CW and the improved practice to 41 kg N ha^?1 year^?1 in CT with W–P and the traditional practice. Because of legume N fixation and increased soil N sequestration rate, diversified crop rotations reduced external N inputs and increased aboveground biomass N removal, N flow, and N balance compared with monocropping, especially in the CT system. As a result, diversified legume–nonlegume crop rotation not only reduced the cost of N fertilization by reducing N fertilization rate, but also can be productive by increasing N uptake and N surplus and environmentally sustainable by reducing N losses compared with nonlegume monocropping, regardless of cultural practices in dryland agroecosystems.     

Nitrogen use efficiency in different rice-based rotations in southern China

Experiments in fields and micro-plots were conducted to investigate the optimal cropping system and nitrogen (N) fertilizer application rate and timing. The treatments consisted of Chinese milk vetch–rice (CMV–R) rotation with five N fertilizer application rates (0, 120, 180, 240, 300 kg N ha^?1) during the rice-growing season, and fallow–rice (F–R) and wheat–rice (W–R) rotations with only one N application rate (240 kg N ha^?1) each. Rice yield increased with increasing N fertilizer application rate under CMV–R rotation, and achieved highest yield under CMV–R180. There is a decreasing trend when N application rate exceeded 180 kg N ha^?1. Rice yield was always higher under CMV–R240 compared to W–R240 and F–R240. During the 2012 rice season, the fertilizer N-use efficiency, residual N fertilizer in soil and N fertilizer recovery efficiency of CMV–R180 reached largest under CMV–R rotation with different N treatments. Furthermore, the fertilizer N-use and recovery efficiencies of CMV–R240 and F–R240 were far higher than those of W–R240. In 2013, fertilizer N-use efficiency was the highest (>?50%) at the heading stage, which was nearly twice as much as the efficiencies during the basal and tillering stages. The N fertilizer loss rate during the basal stage was significantly higher than that at the tillering and heading stages, which was up to 60%. CMV–R rotation with 180 kg N ha^?1 achieved the highest rice yield of 9454 kg ha^?1 and high fertilizer N-use efficiency (40.6%) under a relatively lower N application rate. Therefore, Chinese milk vetch–rice cropping system could be a promising approach for decreasing fertilizer inputs to prevent N pollution problems and increasing rice yield, especially for the intensive rice-based cropping systems in southern China.     

Carbon and nutrient fluxes and balances in Nuba Mountains homegardens,Sudan

Management intensification has raised concerns about the sustainability of homegardens in the Nuba Mountains, Sudan. This study aimed at assessing the sustainability of these agroecosystems following the approach of carbon (C) and nutrient balances. Three traditional (low input) and three intensified (high input) homegardens were selected for monitoring of relevant input and output fluxes of C, nitrogen (N), phosphorus (P) and potassium (K). The fluxes comprised those related to management activities (soil amendments, irrigation, and biomass removal) as well as estimates of biological N₂ fixation, C fixation by photosynthesis, wet and dry deposition, gaseous emission, and leaching. Annual balances for C and nutrients amounted to ?21 kg C ha^?1, ?70 kg N ha^?1, 9 kg P ha^?1 and ?117 kg K ha^?1 in high input homegardens and to ?1,722 kg C ha^?1, ?167 kg N ha^?1, ?9 kg P ha^?1 and ?74 kg K ha^?1 in low input homegardens. Photosynthesis C was the main C input flux with averaged of 7,047 and 5,610 kg C ha^?1 a^?1 in high and low input systems, respectively. Biological N₂ fixation (17 kg N ha^?1 a^?1) was relevant only in low input systems. In both systems, the annual input of 77 kg K ha^?1 through dust was highly significant and annual gaseous C losses of about 5,900 kg C ha^?1 were the main C loss. In both garden types, the removal of biomass accounted for more than half of total nutrient exports of which one-third resulted from weeding and removal of plant residues and two-third from harvest. The observed negative nutrient balances may lead to a long-term decline of crop yields. Among other measures the reuse of C and nutrients in biomass removals during the cleaning of homegardens may allow to partially close C and nutrient cycles.     

Nitrous oxide emissions and herbage accumulation in smooth bromegrass pastures with nitrogen fertilizer and ruminant urine application

Agricultural soils contribute significantly to nitrous oxide (N₂O) emissions, but little data is available on N₂O emissions from smooth bromegrass (Bromus inermis Leyss.) pastures. This study evaluated soil N₂O emissions and herbage accumulation from smooth bromegrass pasture in eastern Nebraska, USA. Nitrous oxide emissions were measured biweekly from March to October in 2011 and 2012 using vented static chambers on smooth bromegrass plots treated with a factorial combination of five urea nitrogen (N) fertilizer rates (0, 45, 90, 135, and 180 kg ha^?1) and two ruminant urine treatments (distilled water and urine). Urine input strongly affected daily and cumulative N₂O emissions, but responses to N fertilizer rate depended on growing season rainfall. In 2011, when rainfall was normal, cumulative N₂O emissions increased exponentially with N fertilizer rate. In 2012, drought reduced daily and cumulative N₂O emission responses to N fertilizer rate. Herbage accumulation ranged from 4.46 Mg ha^?1 in unfertilized pasture with distilled water to 16.01 Mg ha^?1 in pasture with 180 kg N ha^?1 and urine in 2011. In 2012, plots treated with urine had 2.2 times more herbage accumulation than plots treated with distilled water but showed no response to N fertilizer rate. Total applied N lost as N₂O ranged from 0–0.6 to 0.5–1.7 % across N fertilizer rates in distilled water and urine treatments, respectively, and thus, support the Intergovernmental Panel on Climate Change default direct emission factors of 1.0 % for N fertilizer additions and 2.0 % for urine excreted by cattle on pasture.     

Growth and yield response of glasshouse- and field-grown sweetpotato to nitrogen supply

Nitrogen (N) is an essential element for producing optimum crop yields, but negative responses to high N supply are commonly reported in sweetpotato (Ipomoea batatas) production. This study assessed contrasting responses of sweetpotato yield as a result of N application rates of 0, 30, 60, 90, 130, 160 and 230 kg ha^?1 in a glasshouse trial, and rates of 0, 50, 100, 150, 200 and 250 kg ha^?1, equivalent to 160, 210, 260, 310, 360 and 410 kg ha^?1 when soil N supply is included. The glasshouse-grown sweetpotato produced a maximum number and dry-biomass of storage roots, aboveground biomass and leaf area at 130 kg N ha^?1, while leaf N concentration peaked at 90 kg N ha^?1. Further increasing N application to 230 kg ha^?1 did not result in significant change in any of these attributes. In field-grown sweetpotato, leaf and storage root N concentrations increased with increasing N supply. Although N supply had no effect on the number of storage roots, total yield peaked at 260 kg ha^?1. Further increase of N supply reduced the total yield by up to 14% of the maximum yield. With increasing N supply, the glasshouse-grown sweetpotato yield linearly increased with leaf area; the arrangement of the trial permitting light interception to exceed the pot surface area. The yield reduction in field-grown plants was attributed to excess growth of aboveground parts, beyond that needed for efficient light capture. Respirational demand of the aboveground growth occurred at the expense of storage root yields.     

Spatial and temporal nitrogen applications for winter wheat in a loamy soil in south-eastern China

Split application of nitrogen (N), applied by broadcasting, is both time consuming and inconvenient; yet it is widely practised for wheat. Simplified N fertilization is necessary for wheat in south-eastern China. One-time band application was compared with split application using three doses of N (150, 195, and 240 kg ha^?1) in 2014/2015 and 2015/2016. Grain yield and N-use efficiency of winter wheat were determined over two consecutive seasons. A corresponding micro-plot trial using ¹⁵N-labelled urea was conducted only in 2015/2016 to measure the fate of urea-¹⁵N. The two methods showed no difference in grain yield, except at 240 kg ha^?1 of N in 2014/2015. The average grain N concentration (18.2 g kg^?1) was slightly lower in band application than that in broadcast application (19.2 g kg^?1), but there was no significant difference (P > 0.05). In 2014/2015, N apparent recovery efficiency ranged from 33.1 to 49.9%; N agronomic efficiency, from 8.9 to 38.9 kg kg^?1; and N partial factor productivity, from 23.6 to 38.4 kg kg^?1. In 2015/2016, the corresponding values were 29.4–38.6%, 13.5–38.6, and 24.3–33.9 kg kg^?1. In the micro-plot trial, compared to split application, fertilizer N recovery in winter wheat in one-time band application was lower by 26.5% and increased the unaccounted-N loss by 21.7%. Thus, considering environmental impacts, one-time band application of N at sowing is not a suitable alternative to broadcast application in split doses for winter wheat in the loamy soils of south-eastern China.     

Differential retention of carbon, nitrogen and phosphorus in grassland soil profiles with long-term manure application

Liquid hog manure (LHM) is a valuable source of nutrients for farm production. Long-term experimental plots that had received LHM applications of 0, 50, and 100 m³ ha^?1 annually for 20 years were analyzed for total soil C, N and P storage. Applications increased total soil N and P by 1,200 kg N ha^?1 and 850 kg P ha^?1 at 100 m^?3 LHM year^?1, compared to the control treatment. However, C storage did not increase with LHM rates and was lower in the 50 m³ ha^?1 LHM treatment (86 Mg C ha^?1) than in the 0 or 100 m³ ha^?1 treatments (100 Mg C ha^?1). In addition to the limited quantities and high decomposability of the C supplied by LHM, it is hypothesized that LHM stimulated the mineralization of both native soil C and fresh root-derived material. This priming effect was particularly apparent in deeper soil horizons where the decomposability of native C may be limited by the supply of fresh C. This study indicates that while LHM can be a significant source of crop nutrients, it has limited capacity for maintaining or increasing soil C.     

Nutrient transfers by leaching in a no-tillage system through soil treated with repeated pig slurry applications

Repeated pig slurry applications cause accumulation and leaching of soil nutrients and, subsequently, groundwater contamination. The purpose of this study was to evaluate ammonium (NH₄ ⁺–N), nitrate (NO₃ ^?–N), phosphorus (P) and potassium (K) leaching in a sandy soil with a 5-year history of repeated pig slurry applications. The study was carried out in the experimental field of the Universidade Federal de Santa Maria (UFSM) (Federal University of Santa Maria), Santa Maria, Rio Grande do Sul, in the South of Brazil, from 2002 to 2007, in no-tillage system in a Typic Hapludalf soil. Slurry was applied at doses of 0, 20, 40 and 80 m³ ha^?1, which over the 5 years amounted to the addition of 594, 1,188 and 2,376 kg N ha^?1; 508, 1,016 and 2,032 kg P ha^?1 and 216, 432 and 864 kg K ha^?1, respectively. Leachate solutions were collected throughout the period, prepared and then subjected to analysis of NH₄ ⁺–N, NO₃ ^?–N, P and K available in the solution. Repeated applications of pig slurry in a no-tillage system in sandy soil led to the transfer of elements through the leachate solution according to the sequence: nitrate > potassium > ammonium > phosphorus. The transfers of these elements were positively related to the increased volume of leachate solution over the years in addition to the nutrient amounts added by the pig slurry applied over the 60-month period.     

Particulate and active soil nitrogen fractions are reduced by sheep grazing in dryland cropping systems

Sheep (Ovis aries L.) grazing, a cost-effective method of weed control compared to herbicide application and tillage, may influence N cycling by consuming crop residue and weeds and returning N through feces and urine to the soil. The objective of this experiment was to evaluate the effect of sheep grazing compared to tillage and herbicide application for weed control on soil particulate and active soil N fractions in dryland cropping systems. Our hypothesis was that sheep grazing used for weed control would increase particulate and active soil N fractions compared to tillage and herbicide application. Soil samples collected at the 0–30 cm depth from a Blackmore silt loam were analyzed for particulate organic N (PON), microbial biomass N (MBN), and potential N mineralization (PNM) under dryland cropping systems from 2009 to 2011 in southwestern Montana, USA. Treatments were three weed management practices [sheep grazing (grazing), herbicide application (chemical), and tillage (mechanical)] as the main plot and two cropping sequences [continuous spring wheat (Triticum aestivum L.; CSW) and spring wheat–pea (Pisum sativum L.)/barley (Hordeum vulgare L.) mixture hay–fallow; W–P/B–F] as the split-plot factor arranged in randomized complete block with three replications. The PON and MBN at 0–30 cm were greater in the chemical or mechanical than the grazing treatment with CSW. The PNM at 15–30 cm was greater in the chemical or mechanical than the grazing treatment in 2009 and 2011 and at 5–15 cm was greater with W–P/B–F than CSW in 2010. From 2009 to 2011, PON at 0–30 cm and PNM at 15–30 cm reduced from 2 to 580 kg N ha^?1 year^?1 in the grazing and chemical treatments, but the rate varied from ?400 to 2 kg N ha^?1 year^?1 in the mechanical treatment. Lower amount of labile than nonlabile organic matter returned to the soil through feces and urine probably reduced soil active and coarse organic matter N fractions with sheep grazing compared to herbicide application and tillage for weed control. Reduction in the rate of decline in N fractions from 2009 to 2011 compared to the herbicide application treatment, however, suggests that sheep grazing may stabilize N fractions in the long-term if the intensity of grazing is reduced. Animal grazing may reduce soil N fractions in annual cropping systems in contrast to known increased fractions in perennial cropping systems.     

Seeding ratios and phosphate fertilizer on ecosystem carbon exchange of common vetch and oat

With tighter environmental regulations and increasing energy costs over time, approaches to minimize losses from commercially available nitrogen (N) fertilizers have become more critical in recent times. An organically enhanced N fertilizer (OENF), manufactured from organic additives extracted from sterilized biosolids plus ammonium sulfate, was evaluated as an alternative N source relative to commercially available N sources, namely, ammonium sulfate and urea. The formulation was tested on corn in 2012 and 2013 at Jackson and Ames, Tennessee, under no-till and plow lands, respectively. Chemically OENF contains 14.9% N, 4.3% P₂O₅, 18.1% S, 0.6% Fe, and 3.3% OC. The N fertilizer sources were applied at N rates of 0, 85, 128, and 170 kg ha^?1. The P, K, and Zn nutrients were adequately supplied. The OENF and ammonium sulfate produced plant biomass significantly greater than that of urea at N rates of ≥85 kg ha^?1. Despite the fact that less P was supplied to the OENF treatments (36% less P), grain yields from the OENF were similar to those from both ammonium sulfate and urea at N rate of ≤128 kg N ha^?1, but significantly greater than those from urea at 170 kg N ha^?1. The fertilizer type used did not have any significant effects on disease and physical damage to the corn ears at any application rate tested. The OENF could be an alternative N source for crop production and may provide all or some of the P needs for corn production. Therefore, with additional environment benefits of encouraging recycling of municipal and domestic waste and as sources of N, P, S, Fe and organic matter, the use of OENF should be incorporated in various corn production systems.     

Mitigation potential of greenhouse gases under different scenarios of optimal synthetic nitrogen application rate for grain crops in China

Proper management of synthetic nitrogen (N) fertilizer can reduce direct N₂O emission from soil and indirect CO₂ emission from production and transportation of synthetic N. In the late 1990s, the average application rates of synthetic N were 212, 207 and 207 kg ha^?1, respectively, for rice, wheat, and maize in China’s croplands. But research suggests that the optimal synthetic N application rates for the main grain crops in China should be in the range of 110–150 kg ha^?1. Excessive application of synthetic N has undoubtedly resulted in massive emission of greenhouse gases. Therefore, optimizing N application rates for grain crops in China has a great potential for mitigating the emission of greenhouse gases. Nevertheless, this mitigation potential (MP) has not yet been well quantified. This study aimed at estimating the MP of N₂O and CO₂ emissions associated with synthetic N production and transportation in China based on the provincial level statistical data. Our research indicates that the total consumption of synthetic N on grain crops in China can be reduced by 5.0–8.4 Tg yr^?1 (28–47 % of the total consumption) if the synthetic N application rate is controlled at 110–150 kg ha^?1. The estimated total MP of greenhouse gases, including direct N₂O emission from croplands and indirect CO₂ emission from production and transportation of synthetic N, ranges from 41.7 to 70.1 Tg CO₂_eq. yr^?1. It was concluded that reducing synthetic N application rate for grain crops in China to a reasonable level of 110–150 kg ha^?1 can greatly reduce the emission of greenhouse gases, especially in the major grain-crop production provinces such as Shandong, Henan, Jiangsu, Hebei, Anhui and Liaoning.     

Topdressing nitrogen recommendation in wheat after applying organic manures: the use of field diagnostic tools

Nitrogen is the largest input used by farmers, but they often apply excessive quantities of N fertilizer, causing nitrogen losses. In recent years, the management of large quantities of manure and slurry compounds has become a challenge. The aim of this study was to assess the usefulness of the proxy tools Yara N-tester? and RapidScan CS-45 for diagnosing the N nutritional status of wheat crops when farmyard manures were applied. Our second objective was to start designing a N fertilization strategy based on these measurements. To achieve these objectives, two field trials were established with three factors: growing season, three kinds of initial fertilizers [dairy slurry (40 t ha^?1), sheep manure (40 t ha^?1) and conventional (no organic fertilizer on basal dressing and 40 kg N ha^?1 at tillering)] and five N mineral fertilization dose applied at stem elongation. The proxy tools for diagnosing the N nutritional status were used at stem elongation before applying the mineral N. Proxy tool readings as indicators of the nitrogen nutritional status of the field were as good as soil mineral nitrogen (N_min) or Nitrogen Nutrition Index (NNI). When the readings were approximately 65% (as compared to an overfertilized control), the optimal N rate applied at stem elongation was slightly higher (10–20 kg N ha^?1) than the readings at 88%. The first N topdressing at the beginning of tillering could be avoided when manure was applied before sowing, unfolding new possibilities for a later application that might improve the protein content with lower likely fertilization costs.     

Nitrogen and phosphorus benefits from faba bean (Vicia faba L.) residues to subsequent wheat crop in the humid highlands of Ethiopia

Faba bean–wheat rotation is one of the traditional cropping systems in most parts of the temperate, Mediterranean and tropical highland areas. However, the net contribution of legumes to soil nutrient balance is determined by the extent to which crop residue is removed from the field. Therefore, we assessed two possible faba bean residue management scenarios and their role in the faba bean–wheat rotation system in a two-phase field experiment. We further tested to what extent high N₂-fixing and P efficient faba bean varieties could benefit subsequently grown wheat. In the first phase, three improved faba bean varieties (Degaga, Moti, Obse) were grown at four levels of P fertilization (0, 10, 20 and 30 kg P ha^?1) along with local faba bean and reference wheat but without any fertilization. N₂-fixation, soil N balance and P uptake were determined for the faba beans. The N balance was determined via two possible residue management scenarios: scenario-I assumed that all the aboveground biomass is exported from the fields; scenario-II assumed that all the above ground biomass except grains and empty pods is incorporated to the soil. In the second phase, the N and P benefits of faba beans to rotational wheat were assessed. Scenario-I gave a negative net N balance (kg N ha^?1) in the range of ?86.5 ± 5.8 (Degaga) to ?9.4 ± 8.7 (Moti) with significant differences between varieties. Scenario-II showed that all balances were significantly (P < 0.01) improved and the varieties were positively contributing N to the system in the range of 50.6 ± 13.4 (Degaga) to 168.3 ± 13.7 (Moti) kg N ha^?1, which is equivalent to 110–365 kg N ha^?1 in the form of urea (46 % N). In the second crop phase, biomass and grain yield of wheat grown after the faba beans improved significantly (P < 0.05) by 112 and 82 %, respectively compared to the yield of wheat after wheat. Phosphorus application to the preceding faba bean varieties significantly improved total biomass and grain yield of the succeeding wheat (R² = 0.97). The incorporated legume root, nodule and straw clearly played a role in improving wheat yield through N addition via BNF and straw P. The study demonstrates the prospects and importance of improved faba bean germplasm and management as a key component for sustainable wheat based cropping systems in the humid tropical highlands.