Long-term tillage,straw and N rate effects on some chemical properties in two contrasting soil types in Western Canada

Long-term use of soil, crop residue and fertilizer management practices may affect some soil properties, but the magnitude of change depends on soil type and climatic conditions. Two field experiments with barley, wheat, or canola in a rotation on Gray Luvisol (Typic Cryoboralf) loam at Breton and Black Chernozem (Albic Argicryoll) loam at Ellerslie, Alberta, Canada, were conducted to determine the effects of 19 or 27 years (from 1980 to 1998 or 2006 growing seasons) of tillage (zero tillage [ZT] and conventional tillage [CT]), straw management (straw removed [S_Rem] and straw retained [S_Ret]) and N fertilizer rate (0, 50 and 100 kg N ha^?1 in S_Ret, and 0 kg N ha^?1 in S_Rem plots) on pH, extractable P, ammonium-N and nitrate–N in the 0–7.5, 7.5–15, 15–30 and 30–40 cm or 0–15, 15–30, 30–60, 60–90 and 90–120 cm soil layers. The effects of tillage, crop residue management and N fertilization on these chemical properties were usually similar for both contrasting soil types. There was no effect of tillage and residue management on soil pH, but application of N fertilizer reduced pH significantly (by up to 0.5 units) in the top 15 cm soil layers. Extractable P in the 0–15 cm soil layer was higher or tended to be higher under ZT than CT, or with S_Ret than S_Rem in many cases, but it decreased significantly with N application (by 18.5 kg P ha^?1 in Gray Luvisol soil and 20.5 kg P ha^?1 in Black Chernozem soil in 2007). Residual nitrate–N (though quite low in the Gray Luvisol soil in 1998) increased with application of N (by 17.8 kg N ha^?1 in the 0–120 cm layer in Gray Luvisol soil and 23.8 kg N ha^?1 in 0–90 cm layer in Black Chernozem soil in 2007) and also indicated some downward movement in the soil profile up to 90 cm depth. There was generally no effect of any treatment on ammonium-N in soil. In conclusion, elimination of tillage and retention of straw increased but N fertilization decreased extractable P in the surface soil. Application of N fertilizer reduced pH in the surface soil, and showed accumulation and downward leaching of nitrate–N in the soil profile.     

Land management between crops affects soil inorganic nitrogen balance in a tropical rice system

Sustainable production of lowland rice (Oryza sativa L.) requires minimising undesirable soil nitrogen (N) losses via nitrate (NO₃ ^?) leaching and denitrification. However, information is limited on the N transformations that occur between rice crops (fallow and land preparation), which control indigenous N availability for the subsequent crop. In order to redress this knowledge gap, changes in NO₃ ^? isotopic composition (δ¹⁵N and δ¹⁸O) in soil and water were measured from harvest through fallow, land preparation, and crop establishment in a 7 year old field trial in the Philippines. During the period between rice crops, plots were maintained either, continuously flooded, dry, or alternately wet and dry from rainfall. Plots were split with addition or removal of residue from the previous rice crop. No N fertilizer was applied during the experimental period. Nitrogen accumulated during the fallow (20 kg NH₄ ⁺–N ha^?1 in flooded treatments and 10 kg NO₃ ^?–N ha^?1 in treatments with drying), but did not influence N availability for the subsequent crop. Nitrate isotope fractionation patterns indicated that denitrification drove this homogenisation: during land preparation ~50 % of inorganic N in the soil (top 10 cm) was denitrified, and by 2 weeks after transplanting this increased to >80 % of inorganic N, regardless of fallow management. The 17 days between fallow and crop establishment controlled not only N attenuation (3–7 kg NO₃ ^?–N ha^?1 denitrified), but also N inputs (3–14 kg NO₃ ^?–N ha^?1 from nitrification), meaning denitrification was dependent on soil nitrification rates. While crop residue incorporation delayed the timing of N attenuation, it ultimately did not impact indigenous N supply. By measuring NO₃ ^? isotopic composition over depth and time, this study provides unique in situ measurements of the pivotal role of land preparation in determining paddy soil indigenous N supply.     

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.     

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.     

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.     

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.     

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.     

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.     

Biological nitrogen fixation by soybean and fate of applied <Superscript>15</Superscript>N-fertilizer in succeeding wheat under conventional tillage and conservation agriculture practices

Four field experiments were conducted to investigate biological N₂ fixation (BNF) by irrigated soybean under conservation agriculture (CA) as compared with conventional tillage when crop residue (CR) is retained on the soil surface, and the fate of ¹⁵N-labelled fertilizer in succeeding wheat in the semi-arid subtropical soil. Comparable amounts of BNF by soybean were obtained using ¹⁵N isotope dilution and ¹⁵N natural abundance methods, suggesting that the latter, a less costly method could be employed to estimate BNF. Soybean could fix 61–125 kg N ha^?1 (52–85% of total N uptake), depending upon tillage and CR management. Significant increases in BNF by soybean were recorded when CR was retained on the soil surface of CA plots presumably due to better activity of rhizobia because of the relatively cooler rhizosphere environment. Recovery of applied fertilizer N in the soil–plant system at harvest of the wheat crop showed that 36–47% of it was utilized by the crop, 37–49% was left in the soil profile and 5–27% was lost (unrecovered fertilizer N). The recovery of fertilizer N in the soil profile revealed that the majority of it was present in the first 15 cm (54–61%), although downward movement of fertilizer N was also evident up to 120 cm soil depth. These results illustrate enormous benefits of CA practices with CR retained on soil surface on BNF in soybean, and similar patterns in N uptake and translocation from vegetative parts to grain and utilization of applied fertilizer N by wheat in both tillage systems.     

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.     

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.     

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.     

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.     

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.     

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 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.     

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.     

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.     

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.     

Soil aggregates response to tillage and residue management in a double paddy rice soil of the Southern China

Soil aggregate stability is a key indicator of soil quality and environmental sustainability of agroecosystems. The protection of organic material within aggregates against microbial decomposition is regarded as an important process in soil organic carbon stabilization but detailed knowledge about this process is still lacking. The objective of our study was to examine the multiple year effects of plow tillage with residue removed (PT0), plow tillage with residue incorporation (PT), rotary tillage with residue retention (RT), and no-till with residue retention (NT) on soil water stable aggregates (WSA) under a double rice (Oryza sativa L.) cropping system in the Southern China. Results showed that the NT system increased the proportion of >2 mm aggregate fraction, and reduced the proportion of <0.053 mm aggregates at 0–5 cm depth in 2011. Compared with PT0 and PT, significantly higher large macroaggregate (>2 mm) associated-C contributions to TOC were observed in the surface layer (0–10 cm depth) under RT and NT. A significant positive correlation between TOC and macroaggregate (>2 and 2–0.25 mm) associated-C was observed at 0–20 cm soil depth in the paddy rice ecosystem. Therefore, conversion to NT, could enhance the formation of stable macroaggregate, macroaggregates associated-C, and total C contents in paddy soil of Southern China.