High Fertilizer Application Rates Research Articles

Forest residue removal decreases soil quality and affects wood productivity even with high rates of fertilizer application

Forest residues are frequently used as energy sources by Brazilian forest companies. The removal of such residues is known to reduce wood productivity, especially when fertilizer application rate is low. This study aimed to evaluate after two forest rotations the effects of forest residue management on wood productivity when fertilizer is applied at a high rate; and the effect of timber harvest intensity on soil organic matter and microbial activity. We assessed tree growth, soil microbial biomass and activity, and we fractionated soil organic matter (SOM) via its oxidation resistance. These assessments were performed after conducting a field trial comparing harvest residue management over two successive rotations in the same plots. We found no significant effect of treatments on wood productivity when the residues were removed for the first time; however, wood productivity reduced by 15% during the second rotation with residue removal even with high rates of fertilizer application. Further, 40% reduction in microbial biomass and soil respiration was noted with forest residue removal. At the reestablishment time, the SOM in the top soil (0–0.05 m layer) was 25% lower at the site where the forest residues were removed, and this difference increased to 50% at 300 days after the reestablishment. This reduction was found mainly in the SOM labile fraction.

Effects of different fertilization regimes on nitrogen and phosphorus losses by surface runoff and bacterial community in a vegetable soil

Vegetables are major economic crops in China. Their cultivation usually involves high fertilizer application rates leading to significant losses of N and P to the wider environment, resulting in water contamination and low nutrient use efficiency. Hence, it is a matter of urgency to understand the mechanisms and factors that affect N and P losses in vegetable production systems in order to develop optimum fertilization regimes. Different fertilization regimes were applied in a long-term chili (Capsicum spp. L.) production soil to study the effects on nitrogen (N) and phosphorus (P) runoff losses, microbial biomass, microbial community, and crop yields. Three fertilization regimes were implemented: control (no fertilizer; CK), farmer’s fertilization practice (FFP), and site-specific nutrient management (SSNM). A fixed collection device was used to quantify the total volume of water output after each precipitation event. All water samples were analyzed for total nitrogen, ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3−-N), total phosphorus (TP), and available phosphorus (AP). Soil samples were collected for analysis of the physicochemical properties and for DNA extraction after chili harvest. High-throughput sequencing was used to further investigate the relationship between the microbial community and nutrient losses. The SSNM fertilizer regime resulted in a 23.3% yield increase and enhanced agronomic N use efficiency from 11.87 to 15.67% compared with the FFP treatment. Soil available nutrients (i.e., AN and AP) and ATP content increased significantly after SSNM implementation. Under the SSNM regime, N losses decreased by 25.8% compared with FFP but did not lead to significantly different P losses. High-throughput sequencing results showed that each treatment formed a unique microbial community structure. VPA results revealed that the microbial community structure was mainly (50.56%) affected by the interactions between N and P. Mantel results indicated that the soil properties that significantly affected soil microbial community structure followed the order: AP, AK, and salinity. Our study has demonstrated that SSNM not only generates lower N losses but also provides higher contents of soil available nutrients and plant yield, which were mainly attributed to the multiple top dressings and meeting of the plants’ demand with adequate nutrient supplies. The combined data showed that the microbial community differentiation between the different fertilizer regimes was mainly linked to the interactions between N and P in the soil.

Different Response Patterns of Soil Respiration to a Nitrogen Addition Gradient in Four Types of Land-Use on an Alluvial Island in China

It has been well documented that nitrogen (N) additions significantly affect soil respiration (R s) and its components [that is, autotrophic (R a) and heterotrophic respiration (R h)] in terrestrial ecosystems. These N-induced effects largely result from changes in plant growth, soil properties (for example, pH), and/ or microbial community. However, how R s and its components respond to N addition gradients from low to high fertilizer application rates and what the differences are in diverse land-use types remain unclear. In our study, a field experiment was conducted to examine response patterns of R s to a N addition gradient at four levels (0, 15, 30, and 45 g N m−2 y−1) in four types of land-use (paddy rice–wheat and maize–wheat croplands, an abandoned field grassland, and a Metasequoia plantation) from December 2012 to September 2014 in eastern China. Our results showed that N addition significantly stimulated R s in all four land-use types and R h in croplands (paddy rice–wheat and maize–wheat). R s increased linearly with N addition rates in croplands and the plantation, whereas in grassland, it exhibited a parabolic response to N addition rates with the highest values at the moderate N level in spite of the homogeneous matrix for all four land-use types. This suggested higher response thresholds of R s to the N addition gradient in croplands and the plantation. During the wheat-growing season in the two croplands, R h also displayed linear increases with rising N addition rates. Interestingly, N addition significantly decreased the apparent temperature sensitivity of R s and increased basal R s. The different response patterns of R s to the N addition gradient in diverse land-use types with a similar soil matrix indicate that vegetation type is very important in regulating terrestrial C cycle feedback to climate change under N deposition.

Estimating the gross budget of applied nitrogen and phosphorus in tea plantations

Abstract To increase crop yield, high fertilizer application rates have generally been used. The residual fertilizers potentially become a source of diffused pollution, and degrade soil and water quality. Such nonpoint source pollution is a major threat to reservoir eutrophication. The best management practices (BMPs) are usually used to prevent eutrophication; however, the environmental distribution of the applied fertilizers has not been understood properly. This could lead to a biased assessment of the rational quantity of nitrogen and phosphorous applied and the selection of BMPs. A field investigation of 32 plantations and 4 forests in the Feitsui Reservoir watershed, Taiwan, was conducted. Storm runoff water and soils were sampled, and a mass balance was used to demonstrate the gross nutrient budget. The results showed that when applying fertilizers of 2700 kg ha−1 in tea plantations only 18.3% of applied nitrogen and 5.5% of applied phosphorus were utilized by tea plants. Less than 5% of applied phosphorus was released in storm runoff, and more than 90% remained in the field. Approximately 30% of the nitrogen was lost through storm runoff, and 52% was stored in the soil mass. Therefore, reducing fertilizer application was recommended as the principal BMP, and collecting and treating storm runoff was suggested for controlling nitrogen pollution. The current management of soil erosion is an efficient measure for controlling phosphorus pollution.

Mulching and Fertilization Effects on Weed Dynamics under Conservation Agriculture-Based Maize Cropping in Zimbabwe

A two-year study was conducted to assess how mulch influences weed dynamics following imposition of different fertilization treatments under three crop establishment options: (i) conventional; (ii) ripping; and (iii) basin, in a two-year maize-legume rotation. Eight treatments were imposed within each crop establishment option and received maize stover mulch applied at 0% or 30% cover before planting maize (Zea mays) or cowpea (Vigna unguiculata) as test crops. Maize received nitrogen (N) at 35, 90, or 120 kg·ha−1 and phosphorus (P) at 14 or 26 kg·ha−1 applied alone or in combination with 4 or 7 t cattle manure·ha−1, while cowpea received 8 or 17 N·kg·ha−1 and similar P rates to maize. Results indicated that both weed biomass and diversity were influenced more by fertilization than method of crop establishment. On treatments under high fertilizer application rates, or previously planted to cowpea weed biomass ranged between 220 and 400 g·m−2 under mulch and 370–510 g·m−2 (no mulch). Here species richness ranged between 7–16 and was dominated by dicotyledons. This was in contrast to biomass ranges of 75–200 g·m−2 in the low fertilized and control plots, where only one or two grass types dominated. Overall, weed densities were 6% to 51% higher under conventional tillage compared to the two conservation agriculture (CA) options, although the data indicated that mulch significantly (p < 0.05) depressed weed density by up to 70%. We concluded that mulching could be a potential mechanism for reducing weeding labor costs for smallholders and the general environmental and health concerns associated with the use of herbicides in CA systems.

Sensitivity of stoichiometric ratios in the Mississippi River to hydrologic variability

AbstractThe ratio of key elements such as nitrogen, phosphorus, and silica determines nutrient limitations that are important to regulating primary productivity and species composition in aquatic ecosystems. The flux of these nutrients in streams, as dissolved constituents or as particulate matter, is sensitive to variability in flow conditions. Most previous research on nutrient flux and hydrologic variability has focused on the response of individual elements, especially nitrogen, to changes in flow over time. This study examines how the ratios of total nitrogen to total phosphorus (N:P) and total nitrogen to dissolved silica (N:Si) respond to hydrologic variability in the Mississippi‐Atchafalaya River Basin. A doubling of the discharge by the Mississippi and Atchafalaya Rivers to the Gulf of Mexico is found to increase the N:P by 10% and the N:Si by 4%. Analysis of data from upstream stations indicates that the N:P increases with discharge in subbasins with intensive row crop agriculture and high fertilizer application rates but is less predictable in other subbasins. Conversely, the response of N:Si to discharge does not vary predictably with the land use characteristics of the subbasin. The response of the nutrient ratios to variability in flow may be linked to the different sources and sinks of each nutrient, as well as the difference between the dominant transport pathways of each nutrient. High‐resolution data and models that describe the dissolved and particulate nutrient cycling are needed to assess the relative contribution of different drivers to these observed patterns and to identify the response of nutrient ratios to hydrologic variability under future land use and climate change.

Measurements of N2O emissions from different vegetable fields on the North China Plain

Few studies have measured the N2O emission fluxes from vegetable fields. In order to identify the characteristics and the influencing factors of N2O emissions from different vegetable fields, we measured N2O emissions for a full year from four typical fields, including an open-ground vegetable field that has produced vegetables for over 20 years (OV20), a recently developed open-ground vegetable field that was converted from a maize field three years earlier (OV3), a recently developed greenhouse vegetable field that was converted from a maize field 3 years earlier (GV3) and a typical local maize field (Maize). Four different fertilization treatments were set additionally in the recently developed open-ground vegetable field. These were: no fertilizer or manure (OV3_CK), manure only (OV3_M) and the combination of manure with different rates of chemical fertilizer application (OV3_MF1 and OV3_MF3). The results showed that N2O emission fluxes fluctuated between 0.3 ± 0.1 and 912.4 ± 80.0 mg N2O–N m−2 h−1 with the highest emission peak occurring after fertilization followed by irrigation. Nitrogen application explained 64.6–84.5% of the N2O emission in the vegetable fields. The magnitude of the emission peaks depended on the nitrogen application rate and the duration of the emission peaks was mainly associated with soil temperature when appropriate irrigation was given after fertilization. The N2O emission peaks occurred later and lasted for a longer period when the soil temperature was <24 °C in May. However, emission peaks occurred earlier and lasted for a shorter period when the soil temperature was around 25–33 °C from June to August. The annual N2O emissions from the fertilized vegetable fields were 1.68–2.38 times higher than that from the maize field, which had an emission value of 2.88 ± 0.10 kg N ha−1 a−1. The N2O emission factor (EF) of manure nitrogen was 0.07% over the whole year, but was 0.11% and 0.02% in the spring cucumber season and the autumn cabbage season, respectively. The EF of chemical nitrogen was 1.10–1.78% for the vegetable field over the whole year and it was higher in recently developed vegetable field than in the established field (1.54–1.78% vs. 1.10%). Vegetable fields may contribute greatly to the national greenhouse gas inventories due to the high fertilizer application rates, frequent irrigation and an increased number of tillage–planting cycles.

A phosphorus index for use in intensive irrigated areas

AbstractIn irrigated semi‐arid areas, nutrient pollution from agriculture from irrigation return flows is one of the most important surface water quality problems and can lead to eutrophication. In this study, a new phosphorus index called IPreg has been adapted as a management tool for application to irrigated farming systems and then applied within ‘Las Filadas’ drainage basin (Spain) at a plot scale. Two new transport factors related to the irrigation management system were introduced: (i) the seasonal irrigation performance index and (ii) the efficiency of the mean irrigation dose that represents average water losses below the root zone when an average irrigation dose is applied. IPreg includes 10 factors, three of which account for P availability in the soil and seven for P transport processes. The results indicate that 18% of the study area had a high to very high risk of phosphorus loss and 60% at medium risk. Corn and alfalfa had the highest IPreg values under intense irrigation and high fertilizer application rates. IPreg was also higher in phosphorus‐rich soils and in plots treated with organic manure, especially pig slurry.

Ridging, a Mechanized Alternative to Mounding for Yam and Cassava Production

A cassava seedbed preparation field study was established at Fumesua in the forest and Ejura in the forest-savanna transition agroecologies of Ghana in 2004/2005. The experimental design was split plot with three seed bed preparation methods as the main plots and three nitrogen rates as sub plots, with basal application of 45-90 kg ha-1 P205 - K20 on the fertilized plots. A similar study was conducted on yam seedbed preparation in 2003/2004, with a 23 factorial design. Cassava and yams on ridges resulted in highest root and tuber yields, on both Lixisols in the coastal and forest-savanna transition and Acrisols in the forest agro-ecologies. However, yam tuber yield on mounds was not statistically different from yields on ridges. Number of roots per plant was identified as a major contributory factor to the yield increase of cassava on ridges. Seed bed preparation method was, however, not an important determinant of cassava root yield at high rates of fertilizer application of 90-45-90 kg ha-1 N-P205-K20. Planting on mounds resulted in slender, cylindrically shaped cassava roots and yam tubers, while ridging produced oblong shaped roots and tubers. Weeding and fertilizer application were easier on manual ridging than on manual mounds. The study points to ridging as a potential option to mounding for cassava and yam production, with the feasibility of mechanization of ridges to reduce drudgery associated with roots and tuber crop production in the West African sub-region.

Lodging resistance locus prl5 improves physical strength of the lower plant part under different conditions of fertilization in rice ( Oryza sativa L.)

High fertilizer application rates increase grain yield and biomass in rice, but reduces lodging resistance. Lodging resistance locus prl5 enhances pushing resistance through delaying leaf senescence and increasing carbohydrate reaccumulation in stems. This study demonstrates the effects of prl5 under different levels of Nitrogen·Phosphorus·Potassium basal fertilizer application using a chromosome segment substitution line based on the genetic background of Koshihikari, which contains prl5. High fertilizer application rates enhanced pushing resistance of the lower part, but did not consistently affect the pushing resistance of the whole plant. Independent of fertilizer application rates, prl5 enhanced pushing resistances of both the lower part and the whole plants. Plant height, biomass and grain yield were increased by high fertilizer application rates, but stem diameter and the dry weight of basal culms did not show consistent increases as determined over a period of 2 years. In leaves just after heading, chlorophyll (Chl) contents, rather than Rubisco contents, were correlated with fertilizer application rates. At the fully ripe stage, fertilizer application did not affect Chl and Rubisco contents in leaves, while prl5 increased the contents in the second leaf. High fertilizer application rates did not affect the concentration of non-structural carbohydrates (NSCs) in basal culms, but prl5 increased them at the fully ripe stage. These results suggest that fertilizer application reduces lodging resistance by highly elevating the center of gravity, but that prl5 can counteract this effect by enhancing the physical strength of the lower part through delaying leaf senescence and increasing NSC reaccumulation in culms without any effects of different fertilizer application rates.

Winter mulch increases soil CO2 efflux under Phyllostachys praecox stands

Purpose The bamboo species Phyllostachys praecox has been planted in large areas of southern China for the production of edible bamboo shoots. In recent years, high rates of fertilizer application and heavy winter mulch have been employed to achieve an earlier harvest of the shoots and a better economic return. Little is known about the potential impact of these intensive management practices on the receiving environment. Therefore, a field experiment was conducted to quantify the effect of winter mulch on soil CO2 efflux, which contributes to greenhouse gas emissions.

Simulating plant productivity under different organic fertilization practices in a maize/native pasture rotation system in semi-arid NE Brazil

Subsistence agriculture systems in semi-arid regions need to adapt management to rainfall variability within the constraints of low-cost alternatives. Organic fertilization is generally the best possible option to maintain soil fertility as the use of chemical fertilizers is unfeasible due to the high cost and risks of drought and crop failure. However, the effectiveness of organic fertilization will vary according to the quality and rate of organic fertilizer application, rainfall scenarios and decomposition patterns. Simulation models can be used for a quick evaluation of management strategies in many possible scenarios. In this paper a newly developed model (SALSA: Semi-Arid Latin-america Simulation model for Agroecosystems), was used to simulate, along a 3-year period, plant productivity and soil fertility in a maize/native pasture rotation system in semi-arid NE Brazil. The model simulated reasonably well the observed maize productivity in the experimental plots during the 3 years of the study, even under contrasting rainfall conditions and application of organic fertilizers of different qualities (animal manure or Gliricidia sepium prunings). However, model simulations of native pasture biomass productivity did not adequately represent seasonal and fertilizer responses, in part probably due to the seasonal variability of the pasture species composition. The model showed that the effectiveness of organic fertilization depended upon rainfall with largest response in years with intermediate precipitation, and lower responses in wet and dry years. High nitrogen leaching and cloudiness reduced fertilizer use efficiency in wet years even at high rates of fertilizer application (20 t ha −1). Fertilization with G. sepium did not increase aboveground maize productivity compared with animal manure, even though it contained twice the amount of labile fraction. This lack of crop responses to a more labile fertilizer is explained by the large fraction of nitrogen that is leached to deep soil which reduced nitrogen availability in the volume of the soil with the largest amount of crop roots. Management strategies that reduce nitrogen leaching or favor pumping nitrogen from deeper layers (agroforestry) would benefit productivity in this system. The SALSA model proved to have potential as a useful tool to help decisions needed to increase organic fertilization efficiency in NE Brazil even though the base information is scarce compared with modern agriculture.

Management of city aquifers from anthropogenic activities: Example of the Windhoek aquifer, Namibia

As the city of Windhoek is growing rapidly, it has become increasingly obvious that dangers to the underlying groundwater aquifer have become imminent, and need addressing immediately. Water infiltration and the transportation of contaminants from anthropogenic activities through soils into the bedrock and hence the aquifer involve soil maturity, chemical and microbial processes and the climate of a particular area. The thin immature soil horizon (circa 5–20 cm) over the Windhoek schist implies that most areas of the city are built directly on bedrock, making the aquifer vulnerable. Anthropogenic activities from the use of pesticides for weed control, oil spills, toxic chemical spills, dumping of undesired substances by residents and high fertilizer application rates for lawns can lead to the contamination of groundwater. The result of our study show that the soil composition in Windhoek lacks mature clay minerals and is enriched in micas, quartz and albite. Some areas in the northern and southern industrial areas show contamination in heavy metals Pb, Zn, Cu and Ni. To the west of the city, close to the textile factory, soils are contaminated with ammonium compounds. The hydrochemistry of these pesticides and fertilizers can cause severe pollution to the groundwater if the practice is not carefully monitored. In addition, the rapid expansion of uncontrolled settlements without proper sanitation and reticulation has made the problems much more difficult. The geology of the city of Windhoek consists of the Kuiseb Schist, locally known as the “Windhoek Schist” and amphibolites. The Kuiseb schist possesses pervasive cleavage that renders the underlying lithology to be permeable to percolating water and fluids from the surface into the aquifer. The fissility and fracture density of the schist imply that leakage of surface waters, phenols, septic tank spills and industrial contaminants may reach the aquifer in unusually high rainfall years. Organic fuels and oils are much more adverse, as they are able to reside in soils for long periods of time. The weathering of soils in humid climes produces silicic acid, which has an effect in sealing the conduits due to soil generation from rocks; an element lacking in Windhoek due to the arid climate. Thus the close monitoring of all sewage pipes, filling stations, dump sites including cemeteries preferably on a GIS based model is the best possible way to save the aquifer from future pollution.

Mitigation of greenhouse gas emissions from soil under silage production by use of organic manures or slow‐release fertilizer

Abstract. Grassland is a major source of nitrous oxide (N2O) and methane (CH4) emissions in the UK, resulting from high rates of fertilizer application. We studied the effects of substituting mineral fertilizer by organic manures and a slow‐release fertilizer in silage grass production on greenhouse gas emissions and soil mineral N content in a three‐year field experiment. The organic manures investigated were sewage sludge pellets and composted sewage sludge (dry materials), and digested sewage sludge and cattle slurry (liquid materials). The organic manures produced N2O and carbon dioxide (CO2) consistently from time of application up to harvest. However, they mitigated N2O emissions by around 90% when aggregate emissions of 15.7 kg N ha−1 from NPK fertilizer were caused by a flux of up to 4.9 kg N ha−1 d−1 during the first 4 days after heavy rainfall subsequent to the NPK fertilizer application. CH4 was emitted only for 2 or 3 days after application of the liquid manures. CH4 and CO2 fluxes were not significantly mitigated. Composting and dried pellets were useful methods of conserving nutrients in organic wastes, enabling slow and sustained release of nitrogen. NPK slow‐release fertilizer also maintained grass yields and was the most effective substitute for the conventional NPK fertilizer for mitigation of N2O fluxes.

Nitrous oxide emissions from grass swards during the eighth year of elevated atmospheric pCO2 (Swiss FACE)

AbstractEmissions of N2O were measured during the growth season over a year from grass swards under ambient (360 μL L−1) and elevated (600 μL L−1) CO2 partial pressures at the Free Air Carbon dioxide Enrichment (FACE) experiment, Eschikon, Switzerland. Measurements were made following high (56 g N m−2 yr−1) and low (14 g N m−2 yr−1) rates of fertilizer application, split over 5 re‐growth periods, to Lolium perenne, Trifolium repens and mixed Lolium/Trifolium swards. Elevated pCO2 increased annual emissions of N2O from the high fertilized Lolium and mixed Lolium/Trifolium swards resulting in increases in GWP (N2O emissions) of 179 and 111 g CO2 equivalents m−2, respectively, compared with the GWP of ambient pCO2 swards, but had no significant effect on annual emissions from Trifolium monoculture swards. The greater emissions from the high fertilized elevated pCO2Lolium swards were attributed to greater below‐ground C allocation under elevated pCO2 providing the energy for denitrification in the presence of excess mineral N. An annual emission of 959 mg N2O‐N m−2 yr−1 (1.7% of fertilizer N applied) was measured from the high fertilized Lolium sward under elevated pCO2. The magnitude of emissions varied throughout the year with 84% of the total emission from the elevated pCO2Lolium swards measured during the first two re‐growths (April–June 2001). This was associated with higher rainfall and soil water contents at this time of year. Trends in emissions varied between the first two re‐growths (April–June 2001) and the third, fourth and fifth re‐growths (late June–October 2000), with available soil NO3− and rainfall explaining 70%, and soil water content explaining 72% of the variability in N2O in these periods, respectively. Caution is therefore required when extrapolating from short‐term measurements to predict long‐term responses to global climate change. Our findings are of global significance as increases in atmospheric concentrations of CO2 may, depending on sward composition and fertilizer management, increase greenhouse gas emissions of N2O, thereby exacerbating the forcing effect of elevated CO2 on global climate. Our results suggest that when applying high rates of N fertilizer to grassland systems, Trifolium repens swards, or a greater component of Trifolium in mixed swards, may minimize the negative effect of continued increasing atmospheric CO2 concentrations on global warming.

Effect of soil salinity on population structure of fluorescent pseudomonads in spinach rhizosphere

Use of PGPR (plant growth-promoting rhizobacteria) for stimulating plant growth and for the biological control of soil-borne diseases is necessary mainly in fields with intensive cropping. The intensive cultivation systems in horticulture have generally led to soil salinity due tp the high rates of fertilizer application. Therefore, the high concentration of inorganic salts accumulated in the plant rhizosphere is likely to be a factor of salinity stress affecting both roots and root-associated rhizobacteria. In a previous report (Matsuguchi and Sakai 1995), we observed that high salinity of soil had induced a significant decrease in the populations of fluorescent pseudomonads in spinach roots. Furthermore, the adverse effect of high salinity of soil was more pronounced on Pseudomonas fluorescens strains than on Pseudomonas putida strains, resulting in an alteration of the composition of fluorescent pseudomonads in the roots where vP. putida} predominated. The objective of the present study was to determine the effect of soil salinity on the population structure, at the strain level, of fluorescent pseudomonad species colonizing spinach roots.

Humate-Based Biostimulants Do Not Consistently Increase Growth of Container-Grown Turkish Hazelnut

Abstract Humate-based products have been aggressively marketed to nursery producers as biostimulants which increase plant growth. Reports of their effect on container-grown trees in organic substrate are few. We tested four distinct types of biostimulants on top and root growth of Turkish hazelnut (Corylus colurna L.), grown in containers with pine-bark substrate. Treatments included: 1) an untreated control; 2) humate, applied as a dry topdress; 3) humate, formulated as a wettable powder and applied as a substrate drench; 4) humate, applied as a pre-plant root soak; 5) humate, to which various purported root growth-promoting additives had been added, also applied as a root soak. All treatments were tested within low, medium, and high fertilizer application regimes. No treatment increased top growth compared to untreated trees, and the root-soak treatments had the lowest top growth. At high and low fertilizer application rates, root length was similar for all treatments except for root-soak treatments, which had lower root lengths. At the medium fertilizer rate, root length was greatest for trees treated with granular humate applied as a dry topdressing and lowest for trees treated with root soaks.

Impact of Alternative Farm Management Practices on Nitrogen Pollution of Groundwater: Evaluation and Application of CENTURY Model

AbstractAn important environmental issue for Canadian agriculture is groundwater‐N pollution. Addressing this issue requires understanding the impact of farm management practices on nitrate leaching, but empirical studies are limited by resource and time constraints. The CENTURY model was adapted to southwestern Ontario agricultural conditions and then used to predict short‐ to medium‐term effects of crop choice and crop rotation pattern, fertilizer management, and tillage practice on N leaching. CENTURY model evaluation suggests that aboveground C production (translated into grain yield) and N leaching predicted by CENTURY provide good representation of results from actual field‐measured data. Results suggest that relative reduction in groundwater‐N leached is markedly greater at higher rates of fertilizer application than at lower (below the maximum economic rate of N fertilization) rates. Although tillage may not dramatically affect N leaching, other farm management practices such as crop type and crop rotation choice, along with the carry‐over effects of these management activities on mineralization of soil organic matter, may have a significant effect on N leaching from the root zone.

Sodium fertilizer application to pasture. 1. Direct and residual effects on pasture production and composition

AbstractResults are given on the effect of sodium (Na) fertilizer applied as NaNO3 in five application sat 0 (Nil), 32 (Low) or 64 (High) kg Na ha ‐1yr‐1 and the residual effect of sodium chloride(NaCl) fertilizer applied in the previous year on the growth rate and the chemical composition of herbage cut at fortnightly intervals over the grazing season.Na fertilizer at Low and High rates increased herbage Na contents by 20 and 40% respectively. Magnesium (Mg) content in herbage was increased at Low Na fertilizer application rate but there was no difference between the Nil and the High Na treatments. Calcium (Ca) content was increased in proportion to Na fertilizer level. Potassium (K) content of Nil Na herbage exceeded that of Low and High, but there was no effect of treatment on total harvested K yields. The contents of phosphorus (P), sulphur (S), true protein (TP) and modified acid detergent fibre (MADF) in herbage were not affected, but the dry matter digestibility (DMD) was increased with increasing Na fertilizer level. Applying Na fertilizer at the Low and High levels gave similar increases in water‐soluble carbohydrates (WSC) and ash contents and decreased crude protein (CP) and non‐protein nitrogen (NPN) contents. Net herbage accumulation(fresh and dry weight) was increased by 15 and 26% at the Low and High Na fertilizer application rates respectively.NaCl fertilizer residues from the previous year increased herbage Na, DM, DMD and WSC contents, reduced K contents and did not affect Ca, P, S, CP, TP and NPN contents. Residues from Na fertilizer decreased MADF and ash contents at the Low and High Na application rates.The main and residual effects of Na fertilizer were generally maximal in early season and diminished as the season progressed, with many of the effects eliminated by late season. Proportionally 0·70 of Na applied was recovered in the first two grazing seasons after application. The effects of Na fertilizer on mineral ratios are also described, together with the implications for animal health.

Reducing Nutrient Application Rates for Water Quality Protection in Intensive Livestock Areas: Policy Implications of Alternative Producer Behavior

High rates of commercial fertilizer and animal manure application on cropland have been identified as an important cause of ground and surface water degradation in many areas of the country. Suggested remedies are often based on the idea that fertilization levels are economically irrational for the individual farmer. The received wisdom is that farmers could simultaneously improve their own economic well being and reduce the degradation of the ground and surface waters by fertilizing only to meet crop nutrient needs. Rather than assuming that farmers act irrationally, this study examines the fertilization problem on a mixed crop-livestock farm from the perspective of a risk-averse farmer coping with two key uncertainties: crop yield response to nitrogen applications and the nitrogen content of manure. The effects on fertilization decisions by such a farmer of various policy prescriptions for reducing surface and ground water pollution are examined. The results underscore the importance of understanding producer behavior for the design of economically sound policy.