Model results are analysed for risk management options for sorghum production with a range of N fertilizer rates on three soils of a toposequence in three climatic zones in Burkina Faso. The three levels of analysis are: (a) quantifying the probability distribution of physical and economic yield for a range of fertilizer levels and soil types; (b) quantifying the possible variance reduction by soil heterogeneity or by a combination of soils and N rates; (c) developing a procedure for selecting ‘meaningful diversity’ of soil and N fertilizer combinations.
Tag: nitrogen fertilizers
Conversion of degraded forests to oil palm plantations in the Peruvian Amazonia: Shifts in soil and ecosystem-level greenhouse gas fluxes
The expansion of oil palm (OP) plantations and associated forest clearance can significantly impact greenhouse gas (GHG) fluxes. This study examined carbon stocks and soil GHG emissions (N₂O, CO₂, CH₄) in a degraded forest and a neighboring 17-year-old OP plantation in Peruvian Amazonia, where three nitrogen (N) fertilizer treatments were applied: 0 kg (OPN0), 84 kg (OPN1), and 168 kg (OPN2) per hectare per year. Carbon stocks were measured across different pools, and GHG fluxes and environmental parameters were monitored monthly over 11 months and (bi)daily during fertilizer application, with measurements taken near and far from trees/palms. Ecosystem-scale CO₂ equivalent losses were calculated by balancing carbon stock losses against N₂O emission changes. Findings showed that: (1) N₂O emissions (kg N ha⁻¹ y⁻¹) were highest in the degraded forest (6.7 ± 1.2), where litterfall N inputs were substantial (213 kg N ha⁻¹ y⁻¹). Emissions in OP plantations were significantly lower: OPN0 (0.6 ± 0.2), OPN1 (1.4 ± 0.2), OPN2 (2.3 ± 0.3). (2) Soil respiration (Mg C ha⁻¹ y⁻¹) was 1.4 times higher in the forest (9.1 ± 0.6) compared to OP plantation treatments (OPN0: 7.3 ± 1, OPN1: 5.5 ± 0.5, OPN2: 6.5 ± 0.3). (3) The forest acted as a CH₄ sink (-1.5 ± 0.3 kg C ha⁻¹ y⁻¹), whereas all OP treatments were sources (OPN0: 0.2 ± 0.3, OPN1: 0.7 ± 0.5, OPN2: 0.2 ± 0.4). (4) Carbon stock losses from forest-to-OP conversion were significant (196.8 ± 44.0 Mg CO₂ ha⁻¹ over 15 years) but were partially offset (14–20%) by reduced N₂O emissions. These findings highlight the complex GHG trade-offs associated with OP expansion, reinforcing the need for complementary studies to enhance global GHG assessments.
Effect of spatial variability of Nitrogen supply on environmentally acceptable Nitrogen fertilizer application rates to arrable crops
Current N recommendation schemes are based on the Maximum Economic Yield (MEY), as obtained at “economic optimum’ fertilizer application rates. Environmental standards for the amount of mineral N left in the soil at harvest time will soon restrict fertilizer rates to obtain an Environmentally Acceptable Production (EAP). For MEY, but especially for EAP, spatial variability of N supply in a field which is managed as if it were a homogeneous unit should be taken into account. Degree of spatial variability in N supply should be explicitly taken into account in future discussions of the conflict between environmental and production targets.
Potential economic benefits of modifications to urea that increase yield through reduction in nitrogen losses
Many modifications to urea such as inhibitors, algicides, soluble salts, and acidifying agents have been proposed to overcome losses of urea-N, but little is known about the potential economic benefits and acceptable farm-level prices for modified urea. The objective of this study was to develop and use a method for estimating the potential economic benefits of modifications to urea that reduce N losses and enhance crop yields. The method is applicable for crops with a response to N that is well represented by a quadratic model, and for modifications to urea that do not alter the maximum attainable yield with added N. The increment in profit of farmers with the use of modified urea is determined by the difference in net benefit between modified urea and conventional urea when these fertilizers are used at rates that maximize profit. The increment in profit with modified urea increased linearly with increasing saving of N from loss, decreased with the increasing cost of modifying urea, and increased as the price of conventional urea-N increased. The increased price of N for modified urea, expressed as a percentage increase over the price of conventional urea-N, must be <20% when N saving = 17% of applied N, <40% when N saving = 29% of applied N, and <80% when N saving = 44% of applied N to obtain a positive increment in profit. The results suggest that modified urea would be most economical in environments with high response of the crop to urea-N, high price of conventional urea, and high losses of urea-N that can be prevented by the urea modification
Mixed planted-fallows using coppicing and non-coppicing tree species for degraded acrisols in Zambia
The widespread planting of Sesbania sesban fallows for replenishing soil fertility in eastern Zambia has the potential of causing pest outbreaks in the future. The pure S. sesban fallows may not produce enough biomass needed for replenishing soil fertility in degraded soils. Therefore, an experiment was conducted at Kagoro in Katete district in the Eastern Province of Zambia from 1997 to 2002 to test whether multi-species fallows, combining non-coppicing with coppicing tree species, are better than mono-species fallows of either species for soil improvement and increasing subsequent maize yields. Mono-species fallows of S. sesban (non-coppicing), Gliricidia sepium, Leucaena leucocephala and Acacia angustissima (all three coppicing), and mixed fallows of G. sepium + S. sesban, L. leucocephala + S. sesban, A. angustissima + S. sesban and natural fallow were compared over a three-year period. Two maize (Zea mays) crops were grown subsequent to the fallows. The results established that S. sesban is poorly adapted and G. sepiumis superior to other species for degraded soils. At the end of three years, sole G. sepium fallow produced the greatest total biomass of 22.1 Mg ha1 and added 27 kg ha1 more N to soil than G. sepium + S. sesban mixture. During the first post-fallow year, the mixed fallow at 3.8 Mg ha1 produced 77% more coppice biomass than sole G. sepium, whereas in the second year both sole G. sepium and the mixture produced similar amounts of biomass (1.6 to 1.8 Mg ha1). The G. sepium + S. sesban mixture increased water infiltration rate more than sole G. sepium, but both these systems had similar effects in reducing soil resistance to penetration compared with continuous maize without fertilizer. Although sole G. sepium produced high biomass, it was G. sepium + S. sesban mixed fallow which resulted in 33% greater maize yield in the first post-fallow maize. However, both these G. sepium-based fallows had similar effects on the second post-fallow maize. Thus the results are not conclusive on the beneficial effects of G. sepium + S. sesban mixture over sole G. sepium
Nitrogen fertilizer use in California: Assessing the data, trends and a way forward
Nitrogen fertilizer is an indispensable input to modern agriculture, but it also has been linked to environmental degradation and human health concerns. Recognition of these trade-offs has spurred debate over its use. However, data limitations and misinformation often constrain discussion, cooperative action and the development of solutions. To help inform the dialogue, we (1) evaluate existing data on nitrogen use, (2) estimate typical nitrogen fertilization rates for common crops,(3) analyze historical trends in nitrogen use, (4) compare typical nitrogen use to research-established guidelines and (5) identify cropping systems that have significant influence on the state’s nitrogen cycle. We conclude that a comprehensive grower self-monitoring system for nitrogen applications is required to improve nitrogen-use information and to better support evidence-based decision making. The discussion here presents a primer on the debate over nitrogen fertilizer use in California agriculture.
Response of dry season sorghum to supplemental irrigation and fertilizer N and P on Vertisols in northern Cameroon
A series of trials was conducted to quantify response of dry season transplanted sorghum to water and fertilizer application in order to test the hypothesis that soil moisture limits production more than nutrient supply. The trials were conducted at two field sites representative of a large land area in the Lake Chad Basin of Africa. Water was clearly the limiting factor as grain yield response to two irrigations (10 cm total) was a statistically significant 58% over 3 years. One irrigation during vegetative growth resulted in sorghum grain yield increases of 24–29%. Response to P fertilizer was negligible. Response to N fertilizer was 32% over three environments but was not statistically significant at P < 0.05. Future research should focus on improvements in soil moisture availability, either through increased soil moisture storage or through reduced evaporative losses.
Biomass production of tree fallows and their residual effect on maize in Zimbabwe
The rotation of maize (Zea mays) with fast-growing, N2-fixing trees (improved fallows) can increase soil fertility and crop yields on N-deficient soils. There is little predictive understanding on the magnitude and duration of residual effects of improved fallows on maize yield. Our objectives were to determine the effect of fallow species and duration on biomass production and to relate biomass produced during the fallow to residual effects on maize. The study was conducted on an N-deficient, sandy loam (Alfisol) under unimodal rainfall conditions in Zimbabwe. Three fallow species — Acacia angustissima, pigeonpea (Cajanus cajan), and Sesbania sesban — of one-, two-, and three-year duration were followed by three seasons of maize. Pigeonpea and acacia produced more fallow biomass than sesbania. The regrowth of acacia during post-fallow maize cropping provided an annual input of biomass to maize. Grain yields for the first unfertilized maize crop after the fallows were higher following sesbania (mean = 4.2 Mg ha1) than acacia (mean = 2.6 Mg ha1). The increased yield of the first maize crop following sesbania was directly related to leaf biomass of sesbania at the end of the fallow. Nitrogen fertilizer did not increase yield of the first maize crop following one- and two-year sesbania fallows, but it increased yield following acacia fallows. Nitrogen fertilizer supplementation was not required for the first maize crop after sesbania, which produced high-quality biomass. For acacia, which produced low-quality biomass and regrew after cutting, N fertilizer increased yield of the first post-fallow maize crop, but it had little benefit on yield of the third post-fallow maize crop.