Increased Fertilizer Use Research Articles

Nutrient enrichment effects on mycorrhizal fungi in an Andean tropical montane Forest.

Nitrogen (N) and phosphorus (P) deposition are increasing worldwide largely due to increased fertilizer use and fossil fuel combustion. Most work with N and P deposition in natural ecosystems has focused on temperate, highly industrialized, regions. Tropical regions are becoming more developed, releasing large amounts of these nutrients into the atmosphere. Nutrient enrichment in nutrient-poor systems such as tropical montane forest can represent a relatively large shift in nutrient availability, especially for sensitive microorganisms such as arbuscular mycorrhizal fungi (AMF). These symbiotic fungi are particularly critical, given their key role in ecosystem processes affecting plant community structure and function.To better understand the consequences of nutrient deposition in plant communities, a long-term nutrient addition experiment was set up in a tropical montane forest in the Andes of southern Ecuador. In this study, we investigated the impacts of 7years of elevated N and P on AMF root colonization potential (AMF-RCP) through a greenhouse bait plant method in which we quantified root colonization. We also examined the relationship between AMF-RCP and rarefied tree diversity.After 7years of nutrient addition, AMF-RCP was negatively correlated with soil P, positively correlated with soil N, and positively correlated with rarefied tree diversity. Our results show that AMF in this tropical montane forest are directly affected by soil N and P concentrations, but may also be indirectly impacted by shifts in rarefied tree diversity. Our research also highlights the need to fully understand the benefits and drawbacks of using different sampling methods (e.g., AMF-RCP versus direct root sampling) to robustly examine AMF-plant interactions in the future.

Effects of N application reduction and fertilizing distance on saving fertilizer and improving yield in maize/soybean intercropping system

To study the effect of N supplied levels and fertilization distances on saving fertilizer and improving yield in maize/soybean intercropping system, a field experiment was carried out with three N supplying levels ( RN1: 210 kg N·hm-2, RN2: 270 kg N·hm-2 and CN: 330 kg N·hm-2) and four fertilizing distances (D1: 0 cm, D2: 15 cm, D3: 30 cm and D4: 45 cm, indicating the distance between fertilizing site and maize in narrow row). Compared with CN, the results showed that dry matter accumulation and translocation, and their contribution to grain of post-anthesis maize under RN2 were increased by 1.4%, 23.0% and 16.0%, respectively. Meanwhile, kernel number per ear and grain yield per plant of maize were increased by 1.6% and 4.9%. For soybean, dry matter accumulation and translocation, and their contribution to grain at pre-anthesis under RN2 were increased by 2.1%, 37.9% and 26.9%, respectively. Both of soybean grain number and yield per plant were increased by 7.3%. For the maize-soybean intercropping system, N uptake and use efficiency of RN2 were 5.0% and 44.4% higher than those of CN. The soil N content of maize was raised by 4.1% under RN2, but decreased by 0.8% for soybean. The saving fertilizer and improving yield effect of D2 were the best among all the fertilizing distances. Under RN2, contribution rate of dry matter accumulation to grain after anthesis and kernel number per ear of maize in D2 were 57.2% and 9.4% higher than those of D1. Compared with D4, the contribution rate of dry matter accumulation to grain before anthesis and grain number per plant of soybean in D2 were increased by 335.2% and 2.4%, respectively. For the maize/soybean intercropping system, N uptake and use efficiency of D2 were 15.1% and 112.4% greater than those of D1, and 21.4% and 66.3% higher than those of D4. The total soil N content of maize in D2 was 6.6% higher than that of D1, and the index for soybean was 16.0% higher than that of D4. Appropriate N application reduction and fertilizing distance would be beneficial to transfer dry matter to grain, improve grain number per plant, 100-grain mass and yield, promote N uptake and increase fertilizer use efficiency in the intercropping system, which could achieve the purpose of saving fertilizer and improving yield.

Fertilizers, hybrids, and the sustainable intensification of maize systems in the rainfed mid-hills of Nepal

Abstract In the rainfed mid-hill region of Nepal, most fields receive 2–3 t ha−1 of organic compost application every year. Despite efficient recovery and use of organics in the mixed crop-animal systems that predominant in the mid-hills, depleted soil fertility is widely understood to be a significant constraint to crop productivity, with most farmers achieving maize grain yields below 2 t ha−1. Increased use of fertilizer may arrest and even reverse long-term soil quality degradation, but few farmers in the mid-hills use them at present and existing recommendations are insufficiently responsive to site, varietal, and management factors that influence the productivity and profitability of increased fertilizer use. Moreover, policy makers and development practitioners often hold the perception that returns to fertilizer use in the mid-hills are too low to merit investment. In this study, on-farm experiments were conducted at 16 sites in the Palpa district, Nepal to assess the responsiveness of a maize hybrid (DKC 9081) and an ‘improved’ open-pollinated maize variety (‘OPV’, Manakamana-3) to four nitrogen (N) rates, i.e., 0, 60, 120 and 180 kg ha−1, with each N rate response evaluated at 30:30 and 60:60 kg ha−1 rates of phosphorus (P2O5) and potassium (K2O), respectively. With sound agronomy and high rates of fertilizer (180:60:60 kg N:P2O5:K2O ha−1), grain yields observed in the field experiments exceeded 8 t ha−1 with hybrids and 6 t ha−1 with OPV. Yield levels were lower for OPV than hybrid at every level of applied N, but both genotypes responded linearly to N with partial factor productivity for N (PFPN) ranging from 14 to 19 for OPV versus 26–30 for hybrid, with improved N efficiencies obtained when P and K rates were significantly higher. Averaged across phosphorus (P) and potassium (K) levels, a $ 1 incremental investment in fertilizer increased the gross margin (GM) by $ 1.70 ha−1 in OPV and by $ 1.83 ha−1 in the hybrid. For the full response of N, requires higher rate of P2O5:K2O and vice-versa and full response to P2O5:K2O does not occur if N is absent. These results suggest that, i) degraded soils in the mid-hills of Nepal respond favorably to macronutrient fertilizers – even at high rates, ii) balanced fertilization is necessary to optimize returns on investments in N but must be weighed against additional costs, iii) OPVs benefit from investments in fertilizer, albeit at a PFPN that is 36–47% lower than for hybrids, and, consequently iv) hybrids are an effective mechanism for achieving a higher return on fertilizer investments, even when modest rates are applied. To extend these findings across years and sites in the mid-hills, crop growth simulations using the CERES-maize model (DSSAT) were conducted for 11 districts with historical weather and representative soils data. Average simulated (hybrid) maize yields with high fertilizer rate (180:60:60 kg N:P2O5:K2O ha−1) ranged from 3.9 t ha−1 to 7.5 t ha−1 across districts, indicating a high disparity in attainable yield potential. By using these values to estimate district-specific attainable yield targets, recommended N fertilizer rates vary between 65 and 208 kg N ha−1, highlighting the importance of developing domain-specific recommendations. Simulations also suggest the potential utility of using weather forecasts in tandem with site and planting date information to adjust fertilizer recommendations on a seasonal basis.

Waking the Sleeping Giant: Agricultural intensification, extensification or stagnation in Mali's Guinea Savannah

The World Bank argued that West Africa's Guinea Savannah zone forms part of “Africa's Sleeping Giant,” where increases in agricultural production could be an engine of economic growth, through expansion of cultivated land in sparsely populated areas. The district of Bougouni, in southern Mali, falls within this zone. We used multiple data sources including a panel survey, remote sensing-based land cover classification, population data, and farmer focus group discussions, to investigate whether the area is following a commonly-described pathway of agricultural intensification due to increasing land scarcity. We then used our understanding of historical change to explore plausible future pathways. Bougouni forms part of the expansion zone of the CMDT, which since the mid-1980s has provided support for intensive agricultural systems of cotton-maize rotations with animal traction and use of mineral fertilizer. In the period of the panel survey (1994–2012), cropped land at household level was correlated with household size: households with less than one full team of draft oxen cultivated 0.50ha/family member, while households with two or more teams cultivated 0.82ha/family member (R2>0.8). At the village level, cropped land increases varied with the amount of remaining available land and the importance of off-farm income. We see some intensification in maize and cotton, and corresponding improvements in food self-sufficiency. However, despite increasing fertilizer use, average maize and cotton yields remain around 1600 and 900kg/ha respectively, well below national averages. Other crops are still grown in outfields relying on long fallows with limited nutrient inputs. Thus rather than either intensification or extensification the agricultural situation may be best described as stagnation. This may be due to limited incentives to invest in agriculture when compared to opportunities such as gold mining or small businesses, which (in 2012) contribute at least 25% of household income to ten out of 29 households. In future, cropland expansion will likely continue, which could lead to increased conflict between farmers and transhumant herders, and could lead to increased inequality at village level. Factors mitigating the tendency to land expansion include opportunities for off-farm income and migration, or market opportunities and capacity to produce high-value crops such as mango, cashew, or vegetables. This could preserve some remaining savannah area for grazing use and conservation purposes. Understanding household livelihood systems as part of a network of complex social and ecological factors allows the identification and exploration of multiple viable pathways towards desirable futures.

Determinants of Chemical Fertilizer Use in Nepal: Insights Based on Price Responsiveness and Income Effects

Although overall chemical fertilizer use has grown steadily in Nepal in the past two decades, much of that growth has occurred in the Terai agroecological belt while use has stagnated in the Hills and the Mountains regions. Differences in chemical fertilizer use intensity between the Terai and the latter regions are typically pronounced among medium-to-large-size farmers. Using three rounds of the Nepal Living Standards Survey as well as secondary data, we examine the determinants of inorganic fertilizer (urea and DAP) use, as well as the marginal income returns from fertilizer use at the farm-household level. Similarities in soil and climate between farm locale and Agriculture Research Station locale seem to increase demand for fertilizer - even after controlling for distance to those stations. Most important, demand for chemical fertilizer is affected by the real fertilizer price (particularly since the 2003 NLSS survey), but the price response is relatively weaker in the Hills and Mountains, suggesting that returns to fertilizer may be generally low in those regions, and that reducing fertilizer price through subsidies on fertilizer or transportation may not substantially increase fertilizer use. This is confirmed by assessment of the returns to chemical fertilizer use estimated through generalized propensity score matching and ordinary propensity score matching. The findings cast doubt on the effectiveness of fertilizer subsidies as an instrument for stimulating chemical fertilizer use in Nepal, particularly among medium-to-large-scale farmers in the Hills, and point toward alternative measures like increased research and development into technologies that raise overall returns to chemical fertilizer.

Effect of Split Fertilization on Subsurface Water Quality in Wild Blueberry Fields

Abstract. The majority of wild blueberry ( Ait.) fields are situated in acidic soils, having poor water holding capacities, weed patches, gentle to severe topography, and substantial proportion of bare spots, which emphasize the need for variable rate split (VRS) fertilization. Two commercial wild blueberry sites were selected in Nova Scotia, Canada to evaluate the impact of VRS fertilization on subsurface water contamination. The sites were divided into three sections [VRS section, uniform rate split (URS) section, and uniform rate (UR) section]. Prescription maps were generated with ArcGIS 10.1 software based on slope variation for VRS fertilization. Fertilization was performed based on the prescription maps using variable rate (VR) spreader. Fifty-four lysimeters were installed in VRS, URS, and UR treatment sections to collect subsurface water samples. Subsurface water samples were collected after every heavy rainfall event (>15 mm), and were analyzed for nitrate nitrogen (NO 3 - -N) and ammonium nitrogen (NH 4 + -N) concentrations. Leaf samples were collected from each fertilizer treatment and analyzed for macro and micro nutrients. Results suggested that the VRS treatment significantly decreased (p 3 - -N and NH 4 + -N concentrations in subsurface water samples when compared to URS and UR treatments. Overall for the Cooper site, mean NO 3 - -N leaching under the VRS treatment section were 45% and 47% lower as compared to the URS and UR treatment sections, respectively. However, mean values of NH 4 + -N concentration under the VRS treatment section of the North River site were 38% and 45% lower as compared to the URS and UR treatment sections, respectively. Results revealed that the VRS treatment did not have any negative effect on leaf nutrient concentrations. The VRS fertilization saved almost 40% in this study. Results demonstrated that the VRS fertilization in wild blueberry fields can increase fertilizer use efficiency and reduce water contamination via subsurface leaching.

Impact of Weather Index Insurance on Household Demand for Fertilizer in Tigray Region

Agriculture is a risky business. And Ethiopia is one of the few countries in the world that has been ravaged by extreme drought for a number of years and stared its renaissace and development recently. According to Wondifraw Zerihun et al. 2014 on their document regarding African Economic Outlook, in 2012/13 fiscal year, Ethiopia’s economy grew by 9.7%, the tenth year in a row of robust growth. In 2012, Ethiopia was the twelfth fastest growing economy in the world. Average annual real GDP growth rate for the last decade was 10.9%. Agriculture, which accounts for 42.7% of GDP, grew by 7.1, in order to accelerate this economic growth and minimize the weather related agricultural shocks index insurance program is being developed in Ethiopia. Hence the study aimed to investigate the impact of index insurance on farmers demand for fertilizer by using panel data of HARITA project of 2010/11 household survey in Tigray region. The study hypothesized that index insurance provision induces farmers to increase fertilizer demand which is profitable, but risky. To achieve the objectives of the study both descriptive and econometric techniques were used. The study employed random effects model with difference- in- difference estimator to see the impact of index insurance on fertilizer demand. Amount of fertilizer used was the dependent variable. Results of the random effect model showed that weather index insurance has positive significance (at 10% level) impact on fertilizer demand. The sign of the variable indicates that insurance purchaser’s fertilizer demand is more than that of non-purchasers. And purchasing index insurance leads to increase demand for fertilizer by 33 percent. Therefore, the estimated coefficient of the variable was positive sign as expected. Based on the result, the study recommends that weather index insurance program should expand in all the drought prone areas of this region, then they will become confident to adopt or increase fertilizer use, through this productive capacity and living standard, the rural society will improve over time. Finally, this study is left open for further research as index insurance is at its early stage in the study area, so there should be continuous follow up and research on this area.Keywords: difference-in-difference, Fertilizer, HARITA, Random effect, Weather index insurance

Historical trade-offs of livestock’s environmental impacts

Human demand for animal products has risen markedly over the past 50 years with important environmental impacts. Dairy and cattle production have disproportionately contributed to greenhouse gas (GHG) emissions and land use, while crop demands of more intensive systems have increased fertilizer use and competition for available crop calories. At the same time, chicken and pig production has grown more rapidly than for ruminants, indicating a change in the environmental burden per animal calorie (EBC) with time. How EBCs have changed and to what extent resource use efficiency (RUE), the composition of animal production and the trade of feed have played a role in these changes have not been examined to date. We employ a calorie-based perspective, distinguishing animal calorie production between calories produced from feedcrop sources—directly competing with humans for available calories—and those from non-feed sources—plant biomass unavailable for direct human consumption. Combining this information with data on agricultural resource use, we calculate EBCs in terms of land, GHG emissions and nitrogen. We find that EBCs have changed substantially for land (−62%), GHGs (−46%) and nitrogen (+188%). Changes in RUE (e.g., selective breeding, increased grain-feeding) have been the primary contributor to these EBC trends, but shifts in the composition of livestock production were responsible for 12%–41% of the total EBC changes. In addition, the virtual trade of land for feed has more than tripled in the past 25 years with 77% of countries currently relying on virtual land imports to support domestic livestock production. Our findings indicate that important tradeoffs have occurred as a result of livestock intensification, with more efficient land use and emission rates exchanged for greater nitrogen use and increased competition between feed and food. This study provides an integrated evaluation of livestock’s impact on food security and the environment.

Quantitative Assessment of the Human Appropriation of Net Primary Production (HANPP) in the Coastal Areas of Jiangsu, China

Global increases in population and consumption have raised concerns regarding the sustainability of the current and future use of natural resources. The human appropriation of net primary production (HANPP) provides a useful measure for determining human-derived alterations in the amount of biomass that is available in ecosystems each year. HANPP was calculated based on vegetation modelling, agricultural statistics, and remote sensing data on land use and land cover to assess the human impacts on ecosystems in the coastal areas of Jiangsu, China. The results showed that HANPP increased from 332 g·C/m2/year in 2000 to 442 g·C/m2/year in 2010, with an average annual increase of 2.9%. The proportion of appropriated net primary production increased from 50.3% to 71.0% of NPPpot, mainly driven by HANPPharv (harvested NPP) with an increase from 45.2% to 61.3% of NPPpot. Additionally, the spatial variation in average HANPP was striking among counties in the observed period with the lowest and highest values of 21.8% and 63.8% of NPPpot, respectively. Further analysis showed that observed levels of HANPP are high due to a high level of biomass harvest from cropland and the increases in fertilizer use, farmland irrigation rate and population and economic growth explain the trends in HANPP in the coastal areas of Jiangsu.

Factors Affecting the Fertilizer-use Decision of Maize Farmers in Ghana

<p>This work examines the factors that influence whether or not a farmer applies inorganic fertilizer in the Ghanaian context. Current maize yields in Ghana average only one-third of their estimated potential, but this yield gap can be reduced by improving farming practices and growing conditions in Ghana; specifically, yields in Ghana can likely be increased by intensifying the use of inorganic fertilizer, other inputs, and irrigation systems. Recently, Ghana introduced a fertilizer subsidy program to help increase fertilizer-use rates. This paper examines alternate instruments for increasing fertilizer use by determining farm-holder characteristics correlated with inorganic fertilizer use. The results show that the farmer's distance from the closest weekly market, whether the farmer has a pre-harvest contract, and whether the farmer has property rights on the field have a significant effect on fertilizer use.</p>

Yield and Production Gaps in Rainfed Wheat, Barley, and Canola in Alberta.

Improving crop yields are essential to meet the increasing pressure of global food demands. The loss of high quality land, the slowing in annual yield increases of major cereals, increasing fertilizer use, and the effect of this on the environment all indicate that we need to develop new strategies to increase grain yields with less impact on the environment. One strategy that could help address this concern is by narrowing the yield gaps of major crops using improved genetics and management. The objective of this study was to determine wheat (Triticum spp. L.), barley (Hordeum vulgare L.), and canola (Brassica napus L.) yields and production gaps in Alberta. We used 10 years of data (2005–2014) to understand yield variability and input efficiency at a farmers’ specified level of management, and the yield potential under optimal management to suggest appropriate pathways for closing yield gaps. Significant management gaps were observed between attainable and actual yields of rainfed wheat (24%), barley (25%), and canola (30%). In addition, genetic gaps (i.e., gaps due to genetic selection) in wheat, barley, and canola were 18, 12, and 5%, respectively. Genetic selection with optimal crop management could increase yields of wheat, barley, and canola significantly, with estimated yield gains of 3.42, 1.92, and 1.65 million tons, respectively, each year under rainfed conditions in Alberta. This paper identifies yield gaps and offers suggestions to improve efficiency in crop production.

Evaluation of phosphate-solubilizing bacteria on the growth and grain yield of rice (Oryza sativa L.) cropped in northern Iran.

This study aimed to evaluate the efficiency of four phosphate-solubilizing bacteria (PSB) on the growth and yield of rice under different soil conditions. Bacterial strains were Rahnella aquatillis (KM977991), Enterobacter sp. (KM977992), Pseudomonas fluorescens and Pseudomonas putida. These studies were conducted on different rice cultivars ('Shiroodi', 'Tarom' and 'Tarom Hashemi') in both pot and field experiments. Measurements started from transplanting and continued throughout the growing season in field experiments. Single PSB inoculations in field trials increased grain yield, biological yield, total number of stemshill(-1) , number of panicleshill(-1) and plant height by 8·50-26·9%, 12·4-30·9%, 20·3-38·7%, 22·1-36·1% and 0·85-3·35% in experiment 1, by 7·74-14·7%, 4·22-12·6%, 6·67-16·7%, 4·0-15·4% and 3·15-4·20% in experiment 2 and by 23·4-37%, 16·1-36·4%, 30·2-39·1%, 28·8-34% and 2·11-4·55% in experiment 3, respectively, compared to the control. Our results indicate that the application of triple super phosphate together with PSB inoculations resulted in reducing the use of chemical fertilizers (about 67%) and increasing fertilizer use efficiency. This study clearly indicates that these PSBs can be used as biofertilizers in ecological rice agricultural systems. To the best of our knowledge, this is first report on the association of Rahnellaaquatilis with rice and also the application of a mathematical model to evaluate the effect of PSBs on rice growth.

Effect of Biochar on Nutrient Leaching in a Young Apple Orchard.

Nutrient leaching from agricultural soils is a worldwide problem that has been implicated in deleterious impacts on the environment. Application of biochar to soil has been proposed as a means to reduce nutrient leaching and improve fertilizer use efficiency. The potential for biochar to reduce nutrient leaching and increase fertilizer use efficiency was tested by applying 47 Mg ha hardwood biochar before replanting a commercial apple () orchard, in the Huon Valley, Tasmania. Passive wick flux meters were installed at the base of the A1 horizon at a depth of 25 cm to monitor leachate volume and the concentration of nutrients leached below the A1 soil horizon over a 38 mo period. Biochar application significantly increased the concentration of phosphorous in the leachate, while having no significant effect on nitrate or potassium concentration. The volume of leachate collected in the flux meters was significantly higher in the biochar treatment, which resulted in significantly higher amounts of potassium and phosphorous being leaching from the biochar treatment than the control. Biochar application had no significant effect on either the concentration or the flux of nitrate leached from the A1 horizon. Nonetheless, nutrient application was well in excess of tree requirements, such that between 53 to 78% of the applied nitrogen, 5 to 11% of the applied phosphate, and 69 to 112% of the applied potassium were leached below the A1 horizon.

A potential tipping point in tropical agriculture: Avoiding rapid increases in nitrous oxide fluxes from agricultural intensification in Kenya

There are national and regional efforts aimed at increasing fertilizer use in sub-Saharan Africa, where nitrogen (N) inputs must be increased by an order of magnitude or more to reach recommended rates. Fertilizer inputs increase N availability and cycling rates and subsequently emissions of nitrous oxide (N2O), a powerful greenhouse gas and the primary catalyst of stratospheric ozone depletion. We established experimental maize (Zea mays L.) plots in western Kenya to quantify the relationship between N inputs and N2O emissions. Mean N2O emissions were marginally, but not significantly, better described by an exponential model relating emissions to N input rate in 2011; in 2012, an exponential relationship provided the best fit compared to linear and other nonlinear models. Most N2O fluxes occurred during the 30 days following the second fertilizer application. Estimates of fertilizer N lost as N2O annually were well below the 1% Intergovernmental Panel on Climate Change default emission factor, ranging from 0.07% to 0.11% in 2011 and from 0.01% to 0.09% in 2012. In both years, the largest impact on annual N2O emissions occurred when inputs increased from 100 to 150 kg N ha−1: fluxes increased from 203 to 294 g N2O-N ha−1 yr−1 in 2011 and from 168 to 254 kg N ha−1 in 2012. Our results suggest that exponential emission responses are present in tropical systems and that agricultural intensification in western Kenya may be managed for increasing crop yields without immediate large increases in N2O emissions if application rates remain at or below 100 kg N ha−1.

The combined effects of fertilizer reduction on high risk areas and increased fertilization on low risk areas, investigated using the SWAT model for a Danish catchment

Some agricultural areas lose considerably more than the average amounts of nutrients to waterways (high risk areas, HRAs) and others considerably less than the average (low risk areas, LRAs). These areas are of great interest when river catchment managers seek to both reduce nutrient loads to lakes and marine areas and to allow intensive agriculture. If HRAs were farmed with decreased inputs of fertilizers the environmental benefit would be larger here than from any other areas, and if LRAs were farmed with increased fertilizer use it could be done here causing less environmental damage than at any other areas. If both these changes were applied within the same catchment they might counter balance each other and give the possibility of intensified farming without causing environmental deterioration. We used the semi-distributed SWAT model to identify both HRAs and LRAs in an intensely farmed lowland catchment in Denmark. These areas are classified as the 10% of the agricultural area leaching, respectively, the most and the least nitrogen. Two scenarios were run for HRAs (reduced fertilizer input by 20%) and LRAs (increased fertilizer input by 20%) separately and two were run where both HRAs and LRAs were included. The scenario results showed that the HRA scenario yielded a decrease (3.3%) in nitrate river load at the catchment scale and that the LRA scenario yielded only a small increase (0.9%). The combined scenarios showed an overall decrease in river nitrate load (2.2%).

Nitrous oxide (N2O) emissions in response to increasing fertilizer addition in maize (Zea mays L.) agriculture in western Kenya

National and regional efforts are underway to increase fertilizer use in sub-Saharan Africa, where attaining food security is a perennial challenge and mean fertilizer use in many countries is <10 % of nationally recommended rates. Increases in nitrogen (N) inputs will likely cause increased emissions of the greenhouse gas nitrous oxide (N2O). We established experimental plots with different rates of N applied to maize (Zea mays) in a field with a history of nutrient additions in western Kenya and measured N2O fluxes. Fertilizer was applied by hand at 0, 50, 75, 100, and 200 kg N ha−1 in a split application on March 22 and April 20, 2010. Gas sampling was conducted daily during the week following applications, and was otherwise collected weekly or biweekly until June 29, 2010. Cumulative fluxes were highest from the 200 kg N ha−1 treatment, with emissions of 810 g N2O–N ha−1; fluxes from other treatments ranged from 620 to 710 g N2O–N ha−1, but with no significant differences among treatments. Emissions of N2O during the 99-day measurement period represented <0.1 % of added fertilizer N for all treatments. Though limited to a single year, these results provide further evidence that African agricultural systems may have N2O emission factors substantially lower than the global mean.

Limestone and phosphogypsum effects on soil fertility, soybean leaf nutrition and yield

Quantifying soil and plant response to surface applied limestone and phosphogypsum (PG) will help promote no-tillage soybean production. Our objective was to determine effects of annual surface application of phosphogypsum and limestone on soil profile chemistry, fertilizer use efficiency, soybean leaf nutrient concentrations, seed yield, and yield components under a no-tillage system (NTS). The study was conducted in the Brazilian Cerrado under field conditions during three growing seasons on an acidic clay loam soil. Four soil remediation treatments [(limestone, lime + phosphogypsum, phosphogypsum and control (no soil correction)] with four fertilizer levels (0, 50, 100 and 150% of recommended P and K fertilizer for soybean) were arranged in a randomized design using a 4 × 4 factorial design. Treatments involving lime application improved soil chemical characteristics of the soil, resulted in significant increases in plant nutrient concentrations, and increased soybean grain yield. In contrast, application of phosphogypsum did not improve plant development conditions and resulted in no significant changes in soil properties or soybean grain yield. Using increased fertilizer application rates for 3 years also produced significant increases in soybean grain yield. Our results imply that, for acidic soils liming NTS is the best practice to increase fertilizer use efficiency. Key words: Calcium carbonate, Glycine max, no-tillage system (NTS), mineral nutrition, soil acidity.

The effect of municipal wastewater irrigation on yield and biomass of canola (Brassica napus L.) and soil chemical properties

The aim of this study was to test if wastewater irrigation can increase fertilizer use efficiency and improve soil fertility without affecting the quality of soils and plants. The present study was carried out in order to investigate the impact of irrigation municipal wastewater on macro nutrient content of soil, biomass and yield of two varieties of canola (Brassica napus L.viz., SLM046 and Ocapi). The studies were done using Entisols sampled to a depth of 0-30 cm from agricultural fields in Boruojerd province (33°54' N, 48°40' W;1620 m above sea level) in Iran. In this experiment, we have used the experimental lysimeters was designed based on the randomized complete block with three municipal wastewater ratio of 100, 50 and 0% (diluted with irrigation water) and four replicates. The results of this experiment showed municipal wastewater irrigation affected significantly soil chemical properties especially in rhizosphere soil and biomass and yield. Application of municipal waste water increased soil salinity, organic matter, exchangeable Na, K, Ca, Mg, plant available phosphorus and decreased soil pH. It can be concluded that municipal wastewater can be used confidently in the short term in agricultural land both as fertilizer source and to increase fertilizer use efficiency for economical aspect.

How does population density influence agricultural intensification and productivity? Evidence from Ethiopia

This study uses household-level panel data on smallholder farmers in Ethiopia to estimate how rural population density (RPD) affects agricultural intensification and productivity. Our results suggest that higher RPD is associated with smaller farm sizes, and has a positive effect on input demand, represented by increased fertilizer use per hectare. Overall, increased input use does not lead to a corresponding increase in staple crop yields, and thus farm income declines as population density increases. This suggests a situation where farmers in areas of high RPD may be stuck in place, unable to sustainably intensify in the face of rising RPD and declining farm sizes.

Moving in the Right Direction? Maize Productivity and Fertilizer Use and Use Intensity in Ghana

The fertilizer subsidy, reintroduced in Ghana in 2008, seems to have led to increased fertilizer use and use intensity among farmers, but there is limited empirical evidence as to whether this increased fertilizer use has reached the optimal intensity level and has contributed to increased productivity. Using cross-sectional data on 630 maize farmers and 645 maize plots in Ghana, this paper provides empirical evidence on the responsiveness of maize yield to fertilizer use and use intensity and the economics of fertilizer use with or without subsidy. Similar to previous studies in Ghana and Africa south of the Sahara, the results show that there is a statistically significant maize yield response (that is, 1 kilogram of nitrogen leads to a yield increase of 22 kilograms per hectare). Despite subsidized prices, the actual application rate for fertilizer adopters (at 44 kilograms of nitrogen per hectare on average) is far below the optimal level (at 225 kilograms of nitrogen per hectare, where the fertilizer price intersects the value of marginal physical product derived from the yield response model). This result suggests limits to fertilizer subsidy as a strategy to increase fertilizer application, productivity, and income among maize farmers in Ghana. Results suggest that fertilizer prices seem not to be the binding constraint in greater fertilizer application and productivity increases in maize. Other factors, including accessibility to modern seed varieties, mechanization, and hired labor, appear to be major obstacles to greater fertilizer application and productivity increases, and these factors would need to be improved to help increase intensity of fertilizer use in both the northern and southern parts of Ghana. Aside from fertilizer, other factors found to positively contribute to higher yield included modern seed variety use, animal manure, herbicide, and the total number of family labor hours spent working in the maize plot. Plots planted with modern varieties have about a 570-kilogram higher yield per hectare than those planted with traditional varieties, while plots fertilized with animal manure have about a 400-kilogram higher yield and plots with herbicide have about a 170-kilogram higher yield than plots without. Significantly higher yields are obtained when fertilizer application is complemented by these inputs. There is no evidence that certified seeds have a significantly higher yield than recycled or uncertified seeds.