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.     

Two approaches for net ecosystem carbon budgets and soil carbon sequestration in a rice–wheat rotation system in China

Few studies have comprehensively evaluated the method of estimating the net ecosystem carbon budget (NECB). We compared two approaches for studying the NECB components on the crop seasonal scale as validated by the soil organic carbon (SOC) changes measured over the 5-year period of 2009–2014. The field trial was initiated with four integrated soil–crop system management (ISSM) practices at different nitrogen application rates relative to the local farmer’s practices (FP) rate, namely, N1 (25 % reduction), N2 (10 % reduction), N3 (FP rate) and N4 (25 % increase) with no nitrogen (NN) and FP as the controls. Compared with the FP, the four ISSM scenarios of N1, N2, N3 and N4 significantly increased rice yields by 9.5, 19, 33 and 41 %, while increasing the agronomic nitrogen use efficiency (NUE) by 71, 75, 99 and 79 %, respectively. The SOC sequestration potentials were estimated to be ?0.15 to 0.35 Mg C ha^?1 year^?1 from the net primary production minus heterotrophic respiration approach and ?0.32 to 0.67 Mg C ha^?1 year^?1 from the gross primary production minus ecosystem respiration approach for the 2010–2011 rice–wheat annual cycle. Similarly, the annual topsoil carbon sequestration rate over 2009–2014 was measured to be ?0.22 Mg C ha^?1 year^?1 for the NN plot and 0.13–0.42 Mg C ha^?1 year^?1 for the five fertilized treatments. Both NECB approaches provided a sound basis for accurate assessment of the SOC changes. Compared to the SOC sequestration rate from the FP, the proposed N3 and N4 scenarios increased the SOC sequestration rates while also improving rice yield and NUE.     

Long-term effects of fertilization and manuring on groundnut yield and nutrient balance of Alfisols under rainfed farming in India

Drought stress, uncertain and variable rainfall, low soil quality and nutrient deficiencies are among principal constraints for enhancing and sustaining agronomic productivity in rainfed farming in semiarid tropical regions of India. Therefore, long-term (1985–2004) effects of cropping, fertilization, manuring (groundnut shells, GNS; farmyard manure, FYM) and integrated nutrient management practices were assessed on pod yields, nutrient status and balances for a groundnut (Arachis hypogaea) monocropping system. The five nutrient management treatments were: control (no fertilizer); 100 % recommended dose of fertilizer (RDF) (20:40:40 N, P, K); 50 % RDF + 4 Mg ha^?1 GNS; 50 % RDF + 4 Mg ha^?1 FYM and 100 % organic (5 Mg ha^?1 FYM). All treatments were replicated four times. The experiment was conducted at Anantapur district, Andhra Pradesh on an Alfisol using a Randomized Complete Block design. The gap in pod yields between control and different nutrient treatments widened with increase in duration of cultivation. Use of diverse fertilizer and manurial treatments produced significantly higher yields than control (P < 0.05). Amount and distribution of rainfall during critical growth stages was more important to agronomic yield than total and seasonal rainfall. Thus, the amount of rainfall received during pegging stage (r = 0.47; P < 0.05) and pod formation stage (r = 0.50; P < 0.05) was significantly correlated with the mean pod yields. Whereas, use of diverse fertility management practices improved nutrient status in soil profiles (N, P, K, S, Ca, Mg, Zn, Fe, Mn and B) after 20 years of cropping, yet soil available N, K and B remained below the critical limits. Long-term cultivation also caused deficiency of S, Zn and B, which limited the groundnut productivity. Crop removal of N, P and K during 20 years of cultivation was more in 50 % RDF + 4 Mg ha^?1 GNS at 523, 210 and 598 kg ha^?1, respectively. With the exception of control, there was a positive nutrient balance of NPK in all other treatments. Higher positive balance of N and K were observed in 50 % RDF + 4 Mg ha^?1 GNS (616 and 837 kg ha^?1, respectively), and those of P in 100 % RDF (655 kg ha^?1) treatment. There was also a net depletion of available S, Zn, Cu and Mn, but a buildup of available Ca, Mg and Fe. Application of equal amount of GNS was as effective as or even better than FYM in terms of pod yields and nutrient buildup in the soil.     

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.     

Wheat nutrient response functions for the East Africa highlands

Wheat (Triticum æstivum L.) is an important East Africa highland crop but yields are low. Information is scarce for optimization of fertilizer use. Research was conducted to determine yield response functions for N, P and K, and to diagnose Mg–S–Zn–B deficiencies. The average grain yield increase in Rwanda due to N application was 1.5 Mg ha^?1 with a mean economically optimal rate (EOR) of 68 kg ha^?1 N. In Kenya and Tanzania, yield was increased by 29% with EOR N for two SY but unaffected by N rate for four other SY which on average had 50% of the soil organic C (SOC) as the N-responsive SY. Yield was increased, on average, with application of P and K by 0.47 and 0.23 Mg ha^?1, respectively, at EOR in Rwanda but effects were inconsistent for other SY where soil test K was higher than in Rwanda. Application of Mg–S–Zn–B resulted in 0.46 Mg ha^?1 more yield in Rwanda but did not affect yield at other SY where the average soil test values for these nutrients was 35% higher than in Rwanda. If the financially constrained farmer opts to apply the affordable fertilizer to twice as much land at 50% EOR compared with 100% EOR, the mean yield increase is reduced by 27% but production and PCR are increased by 43 and 72%, respectively. Nutrient effects were relatively consistent and positive in Rwanda, but less and less inconsistent elsewhere with generally less SOC, more K–Mg–S–Zn–B availability, and often lower yields.     

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.     

Corn and soybean’s season-long in-situ nitrogen mineralization in drained and undrained soils

Many factors influence nitrogen (N) mineralization in agricultural soils. Our objective was to quantify cumulative (season-long) net N mineralization in corn (Zea mays L.) and soybean [Glycine max (L.) Merr] in a corn-soybean rotation under different N and soil drainage management (drained and undrained) in poorly-drained soils. In-situ incubations were conducted over two growing seasons using a sequential core-sampling technique to measure net N mineralization. Differential drainage was imposed three-years before this study, in which time, the soil lost 2.2 Mg C ha^?1 year^?1 and 0.14 Mg N ha^?1 year^?1 due to tile-drainage. Overall greater total soil organic carbon (TOC) and total soil nitrogen (TN) in the undrained soil resulted in 2.7 times greater net N mineralization compared to the drained soil in the unfertilized control (0N), but the effect of drainage was inconsistent across years with N fertilization. Across all variables, soils mineralized 2.89% of TN in soybean residue and 0.94% of TN in corn residue. Nitrogen fertilization increased mineralization rate, as high as 9.6 kg N ha^?1 day^?1, compared to <2.2 kg N ha^?1 day^?1 for 0N. Overall, net N mineralization was 3.4 times greater with N fertilizer than the 0N, but fertilization made mineralization more variable. The impact of fertilization on boosting mineralization under differential soil drainage needs further refinement if we are to improve decision-making tools for N application based on soil mineralization predictions.     

Historical role of manure application and its influence on soil nutrients and maize productivity in the semi-arid Ethiopian Rift Valley

Maize yield dynamics generally involve temporal changes, because increasing soil organic matter through manure application influences maize yields over the longer term, while inorganic nutrient application controls shorter term yields. These temporal soil properties and yield changes have been measured with long-term experiments. In sub-Saharan Africa (SSA), long-term experiments (more than 20 years) are rare due mainly to lack of funds. Farmers in the semi-arid northern Ethiopian Rift Valley (NERV) apply manure to maize fields in the long term. The relationships between the manure application levels, nutrient supply, soil nutrient levels, maize grain yields, and above-ground plant nutrient uptake levels were investigated by field measurement, interviews with farmers, laboratory analyses, and 2-years’ yield trials. The farmers applied on average 6.0 Mg ha^?1 yr^?1 of manure over 16.8 years on average. Significant linear or curve-linear correlations were found (1) between the annual nutrient supply and soil nutrient levels and (2) between the soil nutrient levels and maize productivities with minor exceptions. The regression equations determined from the yield trials proved 3.0 and 4.0 Mg ha^?1 of maize yields can be expected when soil available N contents were 3.9 and 5.1 mg kg^?1 in an ordinary rainfall year in NERV. For the farmers who apply 6.0 Mg ha^?1 yr^?1 manure, they are recommended to use 30 kg ha^?1 yr^?1 additional Urea to attain 3.0 Mg ha^?1 maize yields. These types of assessment methods do not require much cost, and yet it can provide long-term scientific information in SSA.     

Nitrogen availability to maize as affected by fertilizer application and soil type in the Tanzanian highlands

Enhancing crop production by maintaining a proper synchrony between soil nitrogen (N) and crop N demand remains a challenge, especially in under-studied tropical soils of Sub-Saharan Africa (SSA). For two consecutive cropping seasons (2013–2015), we monitored the fluctuation of soil inorganic N and its availability to maize in the Tanzanian highlands. Different urea-N rates (0–150 kg N ha^?1; split into two dressings) were applied to two soil types (TZi, sandy Alfisols; and TZm, clayey Andisols). In the early growing season, soil mineralized N was exposed to the leaching risk due to small crop N demand. In the second N application (major N supply accounting for two-thirds of the total N), applied urea was more efficient in increasing soil inorganic N availability at TZm than at TZi. Such effect of soil type could be the main contributor to the higher yield at TZm (up to 4.4 Mg ha^?1) than that at TZi (up to 2.6 Mg ha^?1) under the same N rate. The best-fitted linear-plateau model indicated that the soil inorganic N availability (0–0.3 m) at the tasseling stage largely accounted for the final yield. Further, yields at TZi were still limited by N availability at the tasseling stage due to fast depletion of applied-N, whereas yields plateaued at TZm once N availability was above 67 kg N ha^?1. Our results provided a valuable reference for designing the N management to increase yield, while minimizing the potentially adverse losses of N to the environment, in different agro-ecological zones in SSA.     

Crop yields and soil organic carbon fractions as influenced by straw incorporation in a rice–wheat cropping system in southeastern China

In agro-ecosystems, the relationship between soil fertility and crop yield is mediated by manure application. In this study, an 8-year field experiment was performed with four fertilizer treatments (NPK, NPKM₁, NPKM₂, and NPKM₃), where NPK refers to chemical fertilizer and M₁, M₂, and M₃ refer to manure application rates of 15, 30, and 45 Mg ha^?1 year^?1, respectively. The results showed that the NPKM (NPKM₁, NPKM₂, and NPKM₃) treatments produced greater and more stable yields (4.95–5.45 Mg ha^?1 and 0.59–0.75) than the NPK treatment (4.01 Mg ha^?1 and 0.50). Crop yields under the NPKM treatments showed two trends, with a rate of decrease of 0.48–0.83 Mg ha^?1 year^?1 during the first 4 years and a rate of increase of 0.10–0.25 Mg ha^?1 year^?1 during the last 4 years. The soil organic carbon (SOC) significantly increased under all treatments. The estimated annual SOC decomposition rate was 0.35 Mg ha^?1 year^?1 and the equilibrium SOC level was 6.22 Mg ha^?1. Soil total nitrogen (N), available N, total phosphorus (P) and available P under the NPKM treatments increased by 0.15–0.26, 15–33, 0.17–0.66 and 45–159 g kg^?1, respectively, compared with the NPK treatment. Manure application mainly influenced crop yield by affecting the soil TN, available N, and available P, which accounted for up to 64% of the crop yield variation. Taken together, applying manure can determine or at least improve the effects of soil fertility on crop yield in acidic soils in South China.     

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.     

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.     

Net ecosystem CO2 exchange and carbon cycling in tropical lowland flooded rice ecosystem

The seasonal fluxes of CO₂ and its characteristics with relation to environmental variables were investigated under tropical lowland flooded rice paddies employing the open path eddy covariance technique. The seasonal net ecosystem carbon budget was quantified by empirical modelling approach. The integrated net ecosystem exchange (NEE), gross primary production (GPP) and ecosystem respiration (RE) in the flooded rice field was ?448, 811 and 363 g C m^?2 in wet season. Diurnal variations of mean NEE values during the season varied from +3.99 to ?18.50 μmol CO₂ m^?2 s^?1. The daily average NEE over the cropping season varied from +2.73 to ?7.74 g C m^?2 day^?1. The net ecosystem CO₂ exchange reached its maximum in heading to flowering stage of rice with an average value of ?5.67 g C m^?2 day^?1. On daily basis the flooded rice field acted as a net sink for CO₂ during most of the times in growing season except few days at maturity when it became a net CO₂ source. The rate of CO₂ uptake by rice as observed from negative NEE values increased proportionally with air temperature up to 34 °C. The carbon distribution in different component of soil-plant system namely, soil organic carbon, dissolved organic carbon, methane emission, rhizodeposition, carbon in algal biomass, crop harvest and residues were quantified and carbon balance sheet was prepared for the wet season in tropical rice. Carbon balance sheet for tropical rice revealed 7.12 Mg C ha^?1 was cycled in the system in wet season.     

Crop response to manure and fertilizer in Burkina Faso and Niger

Farmyard manure (FYM) is valuable for soil management, especially for soils with <?10 g kg^?1 organic C in semi-arid West Africa. This study determined short-term FYM effects on yield and on response to N, P and K fertilizer for 20 trials in Niger and 28 trials in Burkina Faso involving six crops. The comparisons were of 0 and 2.5 Mg ha^?1 yr^?1 FYM applied in Niger, and of 0 and 5 Mg ha^?1 FYM applied once in 2 years in Burkina Faso. Fertilizer and FYM application alone had little effect on yield in Niger but there was a synergistic effect of fertilizer P with FYM which included increased mean responses to P of, respectively: 0.22 and 0.43 Mg ha^?1 for sorghum grain and fodder (Sorghum bicolor L.); 0.15 and 0.27 Mg ha^?1 for cowpea grain and fodder; 0.16 Mg ha^?1 grain for pearl millet (Pennisetum glaucum L.) when intercropped with cowpea (Vigna unguiculata L.); and 0.39 Mg ha^?1 for groundnut fodder (Arachis hypogea L.). Application of FYM increased pearl millet response to N but decreased legume response to K fertilizer. In Burkina Faso, there was a mean grain yield increase of 0.29 Mg ha^?1 yr^?1 due to FYM and the effect of applying both FYM and fertilizer was additive except for a synergy of N fertilizer plus manure application for maize (Zea mays L.). Therefore, farmers should apply FYM and fertilizer together in Niger but these can be applied alone or together in Burkina Faso with mostly similar effects.     

Assessment of nutrient returns in a tropical dry forest after clear-cut without burning

Tropical dry forests (TDFs) are being deforested at unprecedented rates. The slash/burn/agriculture/fallow-extensive livestock sequence causes significant nutrient losses and soil degradation. Our aim is to assess nutrient inputs and outputs in a TDF area under an alternative management system, for exclusive wood production. The study involved clear-cutting a preserved caatinga TDF site without burning, quantifying nutrients exported in firewood/timber and nutrients returned to the soil from the litter layer plus the slash debris, left to decompose unburned on the soil surface. Before clear-cut, the litter layer on the forest floor contained 6.1 t ha of dry matter (DM). After clear-cut, the aboveground biomass was 61.9 t DM ha^?1 (consisting of 21.5 t DM ha^?1 of commercial wood and 40.4 t DM ha^?1 of clear-cut debris that did not include the underlying litter layer). The litter layer was composed of fine and coarse litter, with turnovers of 0.86 and 0.31 year^?1, respectively, separately measured in uncut control plots during two rainy seasons (Dec-2007/June-2008 and Dec-2008/June-2009). In a single season, its decomposition returned to the soil 48.4, 1.16 and 12.3 kg ha^?1 of N, P and K. The clear-cut debris was mainly composed of branches, 33.4 t ha^?1, bromeliads, 5.63 t ha^?1 and green leaves, 1.32 t ha^?1. In-situ decomposition rates for branches and bromeliads were 0.24 and 1.47 year^?1, respectively. After two rainy seasons the clear-cut debris released 206, 6.5 and 106 kg ha^?1 of N, P and K respectively. This input plus that of the underlying litter layer exceeded exports in the commercial wood, and replenished a soil nutrient stock (0–30 cm) of approximately the same magnitude.     

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.     

Irrigation method and application timing effect on potato nitrogen fertilizer uptake efficiency

Establishment of proper guidelines for irrigation and nitrogen (N) fertilizer management may lead to higher crop fertilizer N use efficiency (FNUE), increasing water conservation and reducing nutrient losses from agricultural systems. The objective of this study was to determine FNUE of potato for three application timings: at planting, emergence and tuber initiation cultivated under three irrigation methods: seepage, subirrigation and sprinkler. A total of 168 kg ha^?1 of N was equally split into three applications of 56 kg ha^?1 as ammonium nitrate (NH₄NO₃). FNUE from each application timing in all irrigation methods was evaluated substituting the conventional N fertilizer by an isotope labeled-ammonium nitrate (¹⁵NH ₄ ¹⁵ NO₃) with 1.18% enrichment in excess. Irrigation method had no significant effects on tuber yield and FNUE. The average tuber yield was 32.1 Mg ha^?1 and overall FNUE was 41%. Across the N application timing treatments, the lowest FNUE was measured for the at-planting application (18%), followed by the emergence N application (44%) and tuber initiation N application (62%). Unaccounted N fertilizer during the potato season amounted to 98 kg ha^?1 from the total 168 kg ha^?1 of N applied. N applied at emergence and tuber initiation were important to increase FNUE and tuber yield, however, some N was required at planting, even with the high potential of N losses for that application.     

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.     

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.     

Current and residual effects of compost and inorganic fertilizer on wheat and soil chemical properties

Restoring soil fertility in smallholder farming systems is essential to sustain crop production. An experiment was conducted in 2011 and 2012 to study the effect of compost and inorganic fertilizer application on soil chemical properties and wheat yield in northwest Ethiopia. Full factorial combinations of four levels of compost (0, 4, 6, 8 t ha^?1) and three levels of inorganic fertilizers (0–0, 17.3–5, 34.5–10 kg N–P ha^?1) were compared in a randomized complete block design with three replications. In 2012, two sets of trials were conducted: one was the repetition of the 2011 experiment on a new experimental plot and the second was a residual effect study conducted on the experimental plots of 2011. Results showed that in the year of application, applying 6 t compost ha^?1 with 34.5–10 kg N–P ha^?1 gave the highest significant grain yield. In the residual effect trial, 8 t compost ha^?1 with 34.5–10 kg N–P ha^?1 gave 271 % increase over the control. Grain protein content increased 21 and 16 % in the current and residual effect trials, respectively, when 8 t compost ha^?1 was applied; it increased 11 and 14 % in the current and residual effect trials, respectively, when 34.5–10 kg N–P ha^?1 was applied. Under the current and residual effects of 8 t compost ha^?1, SOM increased 108 and 104 %; available P 162 and 173 %; exchangeable Ca 16.7 and 17.4 %; and CEC 15.4 and 17.1 %, respectively. Applying 6 t compost ha^?1 with 34.5–10 kg N–P ha^?1 is economically profitable with 844 % MRR.