Smallholders’ Soil Fertility Management in the Central Highlands of Ethiopia: Implications for Nutrient Stocks, Balances and Sustainability of Agroecosystems

Low agricultural productivity caused by soil degradation is a serious problem in the Ethiopian Highlands. Here, we report how differences in soil fertility management between farming systems, based either on enset (Ensete ventricosum) or on teff (Eragrostis tef) as the major crops, affect the extent of nutrient stocks, balances and ecosystem sustainability. We collected information on farmers’ resources and nutrient management practices from stratified randomly selected households in two watersheds in the Central Highlands of Ethiopia. In addition, we collected soil samples from each land use and calculated nutrient stocks, partial and full nutrient balances (N, P and K) for one cropping season. Our results show that farmers in the two farming systems manage their soils differently and that nutrient inputs were positively related to farmers’ wealth status. The watershed with the enset-based system had higher soil N and K stocks than the watershed with the teff-based system, while P stocks were not different. Management related N?and K fluxes were more negative in the teff-based system (?28 kg N ha^?1 yr^?1 and ?34 kg K ha^?1 yr^?1) than in the enset-based system (?6 kg N ha^?1 yr^?1 and ?14 kg K ha^?1 yr^?1) while P fluxes were almost neutral or slightly positive. Within the enset-based system, a strong redistribution of N, P and K took place from the meadows and cereals (negative balance) to enset (positive balances). Although in the teff-based system, N, P and K were redistributed from meadows, small cereals and pulses to maize, the latter still showed a negative nutrient balance. In contrast to nutrient balances at land use level, nutrient balances at the watershed scale masked contrasting areas within the system where nutrient oversupply and deficiencies occurred.     

Nutrient flows and balances in urban and peri-urban agroecosystems of Kano, Nigeria

Nutrient balances are useful indicators to assess the sustainability of farming systems. This study study investigates inflow and outflow of major nutrients in urban and periurban production systems in Kano, Nigeria. To this end, 16 households representing three different urban and peri-urban (UPA) farming systems were studied using the MONQI toolbox (formerly known as NUTMON) to calculate nutrient flows and economic performances. The farm nitrogen (N) balance was positive at 56.6, 67.4 and 56.4 kg farm^?1 year^?1 for commercial garden and crop-livestock (cGCL), commercial gardening and semi-commercial livestock (cGscL) and commercial livestock subsistence field cropping (cLsC) farm types, respectively. The same trend was observed for phosphorus (P) and potassium (K) in all farm types except an annual negative K balance of 16 kg farm^?1 in cGCL. Across the different activities within the farms, land uses had positive N (359, 387 and 563 kg N ha^?1 year^?1) and P (74, 219 and 411 kg P ha^?1 year^?1) balances for all farm types, but again a negative K balance in cGCL with an average loss of 533 kg K ha^?1 year^?1. Partial nutrient balances in livestock production indicated a positive balance for all nutrients across the farms types but were slightly negative for P in cLsC. Commercial livestock keeping (cLsC) was economically more profitable than the other farm types with an average annual gross margin (GM) and net cash flow (NCF) of $9,033 and $935. Cropping activities within cGCL and cGscL had GMs of $1,059 and $194 and NCFs of $757 and $206, respectively, but livestock activities in both farm types incurred financial losses. Potassium inputs were limited under vegetable and crop production of cGCL, threatening long-term K nutrient availability in this system. Overall, the results indicated large annual surpluses of N and P in urban and peri-urban vegetable and crop production systems which pose a potential threat when lost to the environment. Appropriate policies should aim at promoting sustainable production through efficient nutrient management in the Kano UPA sector.     

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.     

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.     

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.     

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.     

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.     

Nitrous oxide emissions as influenced by legume cover crops and nitrogen fertilization

In this study, we measured nitrous oxide (N₂O) fluxes from plots of fall-planted hairy vetch (HV, Vicia villosa) and spring-planted broadleaf vetch (BLV, Vicia narbonensis) grown as nitrogen (N) sources for following summer forage crabgrass (Digitaria sanguinalis). Comparisons also included 60 kg ha^?1 inorganic N fertilizer for crabgrass at planting (60-N) and a control without N fertilizer. Each treatment had six replicated plots across the slope. Fluxes were measured with closed chamber systems during the period between spring growth of cover crops and first-cut of crabgrass in mid-July. HV had strong stand and aboveground biomass had 185?±?50 kg N ha^?1 (mean?±?standard error, n?=?6) at termination. However, BLV did not establish well and aboveground biomass had only 35?±?15 kg N ha^?1. Ratio vegetation index of crabgrass measured as proxy of biomass growth was highest in HV treatment. However, total aboveground biomass of crabgrass was statistically similar to 60-N plots. Fluxes of N₂O were low prior to termination of cover crops but were as high as 8.2 kg N₂O ha^?1 day^?1 from HV plots after termination. The fluxes were enhanced by large rainfall events recorded after biomass incorporation. Rainfall enhanced N₂O fluxes were also observed in other treatments, but their magnitudes were much smaller. The high N₂O fluxes from HV plots contributed to emissions of 30.3?±?12.4 kg N₂O ha^?1 within 30 days of biomass incorporation. Emissions were only 2.0?±?0.7, 3.4?±?1.3 and 1.0?±?0.4 kg N₂O ha^?1 from BLV, 60-N and control plots, respectively.     

Soil nutrient content and nutrient balances in newly-built solar greenhouses in northern China

Soil nutrient content and nutrient balances in newly-built solar greenhouses in the southern part of China??s Loess Plateau were investigated over two consecutive years. Farmers applied manure and inorganic fertilizers at average annual rates of 1,907?kg?N ha^?1, 1,601?kg?P₂O₅?ha^?1 and 1,742?kg?K₂O?ha^?1. Manure accounted for 65?% of the total N input, 57?% of the total P input and 55?% of the total K input. The average annual nutrient surpluses were 1,374?kg?N?ha^?1, 1,468?kg?P₂O₅?ha^?1 and 881?kg?K₂O?ha^?1. Soil organic matter, total N, available P, available K and electrical conductivity (EC) increased significantly across time in the topsoil (0?C20?cm depth), but not in the subsoil (20?C100?cm depth). The nitrate?CN concentrations (mg?N?kg^?1) of the 0?C100?cm depth increased by 163?C336?% over 2?years. The average accumulation of nitrate?CN (kg?N?ha^?1) of the 0?C100?cm depth increased by 241?% and leveled out at 511?kg?N?ha^?1; and it was 1,015?kg?N?ha^?1 in the 0?C200?cm depth. In conclusion, over-fertilization led to large nutrient surpluses in the soil of newly-built greenhouses.     

Nutrients fixation by algae and limiting factors of algal growth in flooded rice fields under semi-arid Mediterranean conditions: case study in Thessaloniki plain in Greece

The aim of this study is to assess the fixation of the major nutrients C, N, P, Ca, Mg, K, Na by algal biomass produced in the rice fields of Thessaloniki plain in Greece under semi-arid Mediterranean conditions and to evaluate the limiting factors for their growth. Measurements were performed in experimental rice-field following the regional conventional practices (C–H treatment): (a) direct sowing, (b) continuous flooding with few intermissions, (c) use of nitrogen fertilizers at 176 kg N ha^?1, and (d) application of herbicides (active ingredients benzofenap and clomazone). Herbicides were not applied in a small part of the field isolated by bunds (C–NH treatment) in order to assess possible limiting effects of herbicides on algae growth. Climatic data, measurements of rice crop characteristics and water quality of the ponded water in the C–H part of the experimental field were also obtained in order to assess the limiting effects of light, temperature and nutrients based on a modelling approach. Green algae were found to be dominant in the specific system. Considering the two treatments, the results showed that herbicides did not affect algae growth probably due to the short period of exposure followed by the continuous flooding. Nutrients fixation by algae for C–H followed the order C (52.1 %) > Ca (5.6 %) > K (3.5 %) > N (2.4 %) > Mg (0.3 %) ≈ Na (0.3 %) > P (0.24 %) with a final dry biomass production at 1,118 kg ha^?1. Based on the measurements and model simulations the most limiting factors under the regional conventional practices of rice cultivation were the temperature at the initial and final stage of rice growing season, the light when the leaf area index of rice was >2 and phosphorus concentration in the ponded water. The mean algae growth rate during the flooding period was estimated at 8.2 kg ha^?1 day^?1, while the maximum rate was estimated at 15.9 kg ha^?1 day^?1 at the initial growth stages of rice before the beginning of intense light limitations from rice crop coverage.     

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.     

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.     

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.     

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.     

Nitrogen balance in a stockless organic cropping system with different strategies for internal N cycling via residual biomass

A major future challenge in agriculture is to reduce the use of new reactive nitrogen (N) while maintaining or increasing productivity without causing a negative N balance in cropping systems. We investigated if strategic management of internal biomass N resources (green manure ley, crop residues and cover crops) within an organic crop rotation of six main crops, could maintain the N balance. Two years of measurements in the field experiment in southern Sweden were used to compare three biomass management strategies: anaerobic digestion of ensiled biomass and application of the digestate to the non-legume crops (AD), biomass redistribution as silage to non-legume crops (BR), and leaving the biomass in situ (IS). Neither aboveground crop N content from soil, nor the proportion of N derived from N₂ fixation in legumes were influenced by biomass management treatment. On the other hand, the allocation of N-rich silage and digestate to non-legume crops resulted in higher N₂ fixation in AD and BR (57 and 58 kg ha^?1 year^?1), compared to IS (33 kg ha^?1 year^?1) in the second study year. The N balance ranged between ??9.9 and 24 kg N ha^?1, with more positive budgets in AD and BR than in IS. The storage of biomass for reallocation in spring led to an increasing accumulation of N in the BR and AD systems from one year to another. These strategies also provide an opportunity to supply the crop with the N when most needed, thereby potentially decreasing the risk of N losses during winter.     

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.     

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.     

Nutrient release dynamics from decomposing organic materials and their mulching-effect on pearl millet yields in a low-input Sahelian cropping system

Organic material inputs for increased crop yields are insufficient in the Sahelian West Africa. There is a need for diversifying organic amendment sources for improved nutrient supply in low-input cropping system. The 2-year study aimed to (1) explore the rates of mass losses and nutrient release dynamics from Acacia tumida prunings (AT) and millet straw (MS) under field conditions, (2) assess termite’s contribution to the decomposition of AT and MS, and (3) ascertain the mulching-effect of these organic materials on pearl millet yields. The study was conducted in Niger using field experiment and litterbag methodology and the data modelled using single exponential decay equations. Under field conditions, mulching with AT and MS increased millet grain yield by 35 and 33%, respectively compared to control. The harvest index (HI) in 2014 increased by 21% compared to that obtained in 2013 with the highest HI being recorded for the AT mulched treatment. The results from litterbag experiment indicated a greater dry mass losses from MS decomposition in 2013 whereas relatively higher mass losses were recorded from AT decomposition in 2014. The differences in mass losses among the organic materials could be related to the interaction of soil moisture dynamics and termites’ population which are positively correlated with mass losses. The contribution of termites to the decomposition was estimated to be 36% for MS and 8% for AT. In 2013, at 126 days after litterbags placement, the amounts of N, P, and K released from MS were 16, 1, and 25 kg ha^?1 of initial nutrient applied, respectively compared with the 22, 1, and 23 kg ha^?1 recorded from AT treatment. During the same period in 2014, the total amounts of N, P and K released from MS were 15, 0.6, and 29 kg ha^?1, respectively compared to the 32 kg ha^?1 of N, 1 kg ha^?1 of P, and 29 kg ha^?1 of K released from the AT treatment. The intrinsic organic material quality could explain markedly the variation in nutrient released among the organic material. These results indicate that Acacia tumida prunings have a potential to provide nutrient through mineralization for enhanced crop yield in the Sahel.     

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.     

Quantification of nitrogen inputs from biological nitrogen fixation to whole farm nitrogen budgets of two dairy farms in Atlantic Canada

Legume biological N fixation (BNF) is a large source of uncertainty in farm N budgets. This study sought to quantify the BNF-N input to two whole farm nitrogen budgets and establish a simple and accurate method for incorporating BNF values as inputs in whole farm N budgets. Nitrogen inputs and outputs as well as flows of N between animal and crop production components were determined for a dairy farm in New Brunswick (NB) and Prince Edward Island (PE) over a two year period. The ¹⁵N natural abundance method was used to determine the %N derived from the atmosphere (%Ndfa) through BNF at both sites. Red clover (Trifolium pratense) at the PE site derived 77 % of its N from BNF and alfalfa (Medicago sativa) collected at both the PE and NB farms derived 72 % of its N from BNF. Total BNF-N present in legume biomass from mixed forage fields measured with the ¹⁵N natural abundance method ranged from 39 to 116 kg N ha^?1 year^?1. A legume dry matter conversion model adjusted with %Ndfa and %N of red clover and alfalfa samples from both farm sites was selected to estimate BNF-N inputs from mixed forage fields on the farms. Averaged across the entire cropland area at each farm site, the BNF-N inputs ranged from 27 to 52 kg N ha^?1 year^?1. The farmgate BNF-N inputs are low in comparison to other studies, possibly due to low legume contents in forage fields. BNF accounted for 18–29 % of farmgate N inputs at the farms. Surpluses of N found at both farm sites ranged from 98 to 135 kg N ha^?1 year^?1, typical to the whole farm N budgets of similar dairy farms.