Use of Modeling to Predict P Accumulation in Winter Wheat and Maize Crop Rotations

Ma et al. (2009) conducted an experiment which involved creating a model to predict the Olson-P levels in soils under cultivation for winter wheat and maize crops in China. They created a model using over 15 years worth of data from crop rotations among 5 provinces of China, which had varying soil composition and climate. Both crops that were fertilized with P and those that were not were included in the study to examine the level of extraction of Olson-P by the crops in the form of grain yield. The unfertilized crops quickly exhausted the soils’ Olson-P content until a level of approximately 3 mg/kg was reached at which removal plateaued. When P fertilizer was applied to the crops, the amount of Olson-P rose and accumulated within the soil at an average rate of 1.21 mg/kg/yr. The model created was determined to be accurate in predicting rates of Olson-P in the soils. — Maria Harwood
Ma, Y., Li, J., Tang, T., Liang, Y., Huang, S., Wang, B., Liu, H., Yang, X., 2009. Phosporus accumulation and depletion in soils in wheat-maize cropping systems: Modeling and validation. Field Crops Research 110, 207–212
Ma et al. used measurements of Olson-P levels and P fertilizer application rates from 5 experiment sites around China spanning over 15 years. Three treatments using no fertilizer, N and P fertilizer, or N, P, and K fertilizer were conducted. The model that was created used data on P fertilizer rates and crop grain yield to predict the levels of Olson-P in the soils. The accumulation rate of Olson-P in soils is dependent upon the P application rate, crop grain yield or removal, and soil pH. The model was validated by comparing its results to another series of long-term studies of crop rotations from around China and India.
The model proved to accurately predict the amount of Olson-P found in the soils for the unfertilized crops. The crops fertilized with a combination of N and P, or N, P, and K did not produce reliable accumulation trends of Olson-P. This was a result of variability in the soil sampling and analysis. The initial value of Olson-P in the soils is important to know so that further calculations can be performed to predict the future levels after crop removal and added P fertilizer. Using this model can help accurately predict Olson-P levels in soils so that costly soil tests can be avoided and the correct level of P fertilizer can be applied.

Use of Modeling to Predict P Accumulation in Winter Wheat and Maize Crop Rotations

Ma et al. (2009) conducted an experiment which involved creating a model to predict the Olson-P levels in soils under cultivation for winter wheat and maize crops in China. They created a model using over 15 years worth of data from crop rotations among 5 provinces of China, which had varying soil composition and climate. Both crops that were fertilized with P and those that were not were included in the study to examine the level of extraction of Olson-P by the crops in the form of grain yield. The unfertilized crops quickly exhausted the soils’ Olson-P content until a level of approximately 3 mg/kg was reached at which removal plateaued. When P fertilizer was applied to the crops, the amount of Olson-P rose and accumulated within the soil at an average rate of 1.21 mg/kg/yr. The model created was determined to be accurate in predicting rates of Olson-P in the soils. — <!–[if supportFields]> CONTACT _Con-3EF86BDE1 \c \s \l <![endif]–>Maria Harwood<!–[if supportFields]><![endif]–>
Ma, Y., Li, J., Tang, T., Liang, Y., Huang, S., Wang, B., Liu, H., Yang, X., 2009. Phosporus accumulation and depletion in soils in wheat-maize cropping systems: Modeling and validation. Field Crops Research 110, 207–212

Ma et al. used measurements of Olson-P levels and P fertilizer application rates from 5 experiment sites around China spanning over 15 years. Three treatments using no fertilizer, N and P fertilizer, or N, P, and K fertilizer were conducted. The model that was created used data on P fertilizer rates and crop grain yield to predict the levels of Olson-P in the soils. The accumulation rate of Olson-P in soils is dependent upon the P application rate, crop grain yield or removal, and soil pH. The model was validated by comparing its results to another series of long-term studies of crop rotations from around China and India.
The model proved to accurately predict the amount of Olson-P found in the soils for the unfertilized crops. The crops fertilized with a combination of N and P, or N, P, and K did not produce reliable accumulation trends of Olson-P. This was a result of variability in the soil sampling and analysis. The initial value of Olson-P in the soils is important to know so that further calculations can be performed to predict the future levels after crop removal and added P fertilizer. Using this model can help accurately predict Olson-P levels in soils so that costly soil tests can be avoided and the correct level of P fertilizer can be applied.

Savings of 19% Net GHG Flux to Atmosphere Possible With Fertilization of Crops in Early Spring

Phillips et al. (2009) conducted an experiment to determine whether the timing of fertilizer application to maize crop in Central North Dakota affects the greenhouse gas (GHG) fluxes during the growing season. Plots were fertilized either in early spring (April 1) or in late spring (May 13). It was hypothesized that the plots fertilized in early spring would produce lower net GHG emissions, due to the lower air and soil temperatures, which inhibit the microbial production and consumption of GHG. The three GHG measured include, methane, carbon dioxide, and nitrous oxide. Fertilization of the plots in early spring had a net GHG flux of 19% less than the plots which were fertilized in late spring. Over 98% of the GHG emissions came from carbon dioxide, as opposed to methane or nitrous oxide. — <!–[if supportFields]> CONTACT _Con-3EF86BDE1 \c \s \l <![endif]–>Maria Harwood<!–[if supportFields]><![endif]–>
Phillips, R., Tanaka, D., Archer, D., Hanson, J., 2009. Fertilizer Application Timing Influences Greenhouse Gas Fluxes Over a Growing Season. Journal of Environmental Quality 38, 1569–1579.

 Phillips et al. measured methane, carbon dioxide, and nitrous oxide gases, in conjunction with soil pH, electrical conductivity, texture, bulk density, total C and N, water holding capacity of the soil, air temperature near soil surface, and soil temperature 10cm below the surface. The plot measurements were taken between 1000 to 1200 hr, during the time period that is most representative of the daily fluxes, 1 to 4 times per week. These factors were measured to determine what was producing the changes in GHG emissions. The experiment was conducted over 5 months on the northern Great Plains in 5 plots, each 0.30 ha, that wer fertilized with urea in early spring, and 5 plots fertilized in late spring.
Both methane and carbon dioxide emissions showed effects from the early versus the late fertilization of the maize crop. The fluxes were greater within the soil for the plots that were fertilized in late spring. The time-integrated net GHG flux for soils that were fertilized in late spring was greater than the soils fertilized in early spring. Nitrous oxide did not show any difference in flux between the two treatments. Carbon dioxide was responsible for over 98% of the total GHG flux emissions. A net GHG flux lost to the atmosphere of 19% could be avoided in central North Dakota if fertilizer is applied to fields in early spring, before temperatures rise above 10°C. When the soil and air temperatures rise above 10°C, the microbial activity in the soil gets stimulated with the addition of urea fertilizer, producing greater GHG emissions.

Use of Computer Systems to Tailor Slurry Application to Specific Agricultural Fields Proves Effective

Schellberg and Lock (2009) conducted a study that designed software and hardware systems to control the application of slurry to grasslands and agricultural crops. They theorized that if the application process of the slurry, utilized as a crop fertilizer, could be controlled to a high degree of accuracy based on a fertilizer application map, specific to the field of cultivation, large N losses to the environment and over-fertilization of the crops would be avoided. This study did not evaluate the effectiveness of their site-specific slurry application techniques in the form of crop yield or spatial distribution of N. Instead, the effectiveness of the software and hardware systems to work together and produce the accurate application levels as determined in the application map were of concern in the study. — <!–[if supportFields]> CONTACT _Con-3EF86BDE1 \c \s \l <![endif]–>Maria Harwood<!–[if supportFields]><![endif]–>
Schellberg, J., Lock, R., 2009. A Site-specific Slurry Application Technique on Grassland and on Arable Crops. Bioresource Technology 100, 280–286.

 Schellberg and Lock used cattle slurry in their two field application experiments on a grassland used for forage and a field of corn. The key issues in applying this technique lay in the ability to determine the local nutrient demand of the plants and the need for an advanced on-field monitoring system tracking the release of the slurry. The authors tackled the latter problem by creating a software and hardware system to actively control the flow rate of the slurry during application. The various parameters that they measured include the dry matter yield, the dry matter content in the harvested material, the plant N content, the estimated N extraction by plants, the mineralized N in the fields, and the calculated N fertilizer. These data were used as input parameters to their software system to ultimately determine the correct amount of N fertilizer, or slurry, to be applied to the varying locations within the field.
This article pointed to the accuracy of the application map as the key to the site-specific application of slurry, although they noted that the size of the grid cells within the field for slurry application have to be significantly small to produce accurate results. There also was a time lag noted within the equipment as it attempted to adjust as it entered a geographic region of the field that required a varying amount of slurry.

15N Content Found in Plants Can Be Used as an Indicator of Excess Compost Application

Yun and Ro (2009) conducted an experiment using Chinese cabbage plants to determine whether the amount of 15N within the plant tissues can be used to indicate the overuse of compost in soil. Compost is an important inexpensive alternative to chemical fertilizers, although the overuse of compost can lead to the same environmental impacts that overuse of N fertilizers have. The amount of nutrients in compost varies depending upon the source, therefore the concentrations of N and P need to be determined before application to soils in order to avoid overuse. Four different amounts of compost were used in the experiment and three areas of plant tissue and the soil were analyzed for 15N content. They determined the amount of 15N found in the plants along with the soil nitrate content can be used to tell if the level of compost application was too high. — <!–[if supportFields]> CONTACT _Con-3EF86BDE1 \c \s \l <![endif]–>Maria Harwood<!–[if supportFields]><![endif]–>
Yun, S., Ro, H., 2009. Natural 15N abundance of plant and soil inorganic-N as evidence for over-fertilization with compost. Soil Biology and Biochemistry 41, 1541–1547.

 Yun and Ro used potted Chinese cabbage plants grown for 42 days in soil amended with a compost made of pig manure mixed with sawdust. Four different rates of compost were applied to the soil; 0, 500, 1000, 1500 mg N/kg. The outer, middle, and inner leaves of the Chinese cabbage plants were analyzed for N content to determine whether the source of N found in the plants was from the compost or the indigenous N soil content. This distinction is key to figuring out if 15N can be used as an indicator of the amount of compost used or if it is only showing the N usage from the soil.
Compost application increased the amount of dry mass accumulation of the cabbage with the lowest application rate, but successive increasing amounts of compost produced no increase in dry mass. Although the amount of dry mass did not increase with added compost, the uptake of N by the cabbage plants did increase in proportion to the amount of compost. The increasing compost amounts also produced greater amounts of 15N found in the cabbage for all applications except the lowest. The inner, younger leaves of the cabbage showed a strong correlation of the 15N levels being derived from the compost, therefore the authors determined the 15N levels found in plants can be used as an indicator of the amount of compost being applied to the soil.

The Three Best Practices to Decrease N Losses in EU-27 Cause High Costs to Farmers, But Are Successful

Oenema et al. (2009) performed a modeling-based experiment to determine the environmental and economic costs of implementing the three most promising measures to abate N losses in agricultural production within the 27 Member Nations of the European Union (EU-27). The three general categories of measures include balanced fertilization (BF), low-protein animal feeding (LNF), and ammonia emissions abatement (AEA), with preferred order of implementation BF, LNF, and AEA. Both practices of BF and LNF were found to decrease N inputs as they simultaneously increased N output in useful products. AEA caused a decrease in ammonia emissions, but this was coupled with an increase in other types of N emissions, therefore not seen to be effective when used alone without other measures. All three measures were not without additional costs to the farmer in time and lost income, as well as to society in the form of higher priced goods.— <!–[if supportFields]> CONTACT _Con-3EF86BDE1 \c \s \l <![endif]–>Maria Harwood<!–[if supportFields]><![endif]–>
Oenema, O., Witzke, H.P., Klimont, Z., Lesschen, J.P., Velthof, G.L., 2009. Integrated assessment of promising measures to decrease nitrogen losses from agriculture in EU-27. Agriculture, Ecosystems and Environment 133, 280–288.

 To determine the environmental effects of the different measures, the MITERRA-EUROPE model was used, along with the CAPRI model to determine the economic costs (Oenema et al. 2009). These three measures were selected based upon their evaluated effectiveness to increase N use efficiency and decrease N losses through ammonia and nitrous oxide emissions to the atmosphere and N leaching into groundwater and surface waters. Nitrogen use efficiency (NUE) is defined as the N output in useful products (harvested crops, milk, meat) as a percentage of the total N inputs (N fertilizer). The three measures were evaluated against the N losses and NUE increases from “business as usual” in 2000 and 2020.
AEA was only considered in conjunction with the other measures because a decrease in ammonia emissions results in “pollution swapping” where N increases in other areas. All three measures were found to have varying degrees of effectiveness across EU-27 given the differences in the type of crop or animal production and soil types, although implementation always resulted in reduction of N losses, but not without costs to farmers and consumers in the form of lost profits and welfare. BF was determined to be the best measure to implement because of its low relative cost and large benefits in the form of decreased N losses, mostly in areas determined as nitrate vulnerable zones (NVZ). LNF had high costs associated with it because in the baseline measures there already was a relatively low amount of N in the animals excretion, therefore lower protein content feed is not a viable solution because the feed already contains close to the optimum amount. AEA also had high costs associated with implementation, but due to the phenomenon of pollution swapping, this measure could only be implemented when coupled with the other measures, further increasing the overall costs. These measures all have been proven to have demonstrable effects on lowering N losses to the environment, but not without decreases to farmers’ income as high as 25% of the total EU spending on agriculture. 

Overuse of N Fertilizers Leads to Nutrient Imbalance and Acidification of Soil in Zhangjiagang County, China

Darilek et al. (2009) conducted a study of the soil fertility parameters in conjunction with information from the county of Zhangjiagang, China, on the amounts of nitrogen, phosphorus, and potassium fertilizers used from 1980 to 2004. Within this county, which is part of the Yangtze River Delta area, there are two dominant types of soil, Cambosols and Anthrosols. Cambosols are found in the northern region near the river, while Anthrosols are prevalent in the southern plains region. Anthrosols experienced such a high increase in pH (or acidification of the soil), due to over-application of N fertilizers and an increase in industrial effluents that the area will be rendered useless for crop production in 25 to 30 years. —<!–[if supportFields]> CONTACT _Con-3EF86BDE1 \c \s \l <![endif]–>Maria Harwood<!–[if supportFields]><![endif]–>
Darilek, J., Huang, B., Wang, Z., Qi, Y., Zhao, Y., Sun, W., Gu, Z., Shi, X., 2009. Changes in soil fertility parameters and the environmental effects in a rapidly developing region of China. Agriculture, Ecosystems and Environment 129, 286-292.

 Jeremy Darilek and his colleagues collected soil samples from around the county of both Cambosols and Anthrosols in 1980, then again in 2004. These samples were analyzed for pH, organic matter, cation exchange capacity, total nitrogen, total phosphorus, available phosphorus, and available potassium. These data combined with information supplied by the county on the rates of N, P, and K fertilizer applied annually were used to determine the effects of the different fertilizers on the soil fertility parameters. The effects of the fertilizers on the environment were not evaluated directly, but were inferred from present knowledge on overuse of fertilizers and how this can lead to N leaching and eutrophication of surrounding water bodies.
The ratio of N:P:K fertilizer applied to the rice and wheat crops grown in this region has increasingly contained excessive amounts of N, above the needed requirements for the crops since 1990. P fertilizer rates have increased, but remain at levels beneficial to the growth of the crops due to a lack of P accumulation in the soil. Also over the years there has been a phasing out of the use of organic fertilizers, and an increased reliance on inorganic fertilizers. Among the two soil types, Anthrosols were found to have a great decrease in pH, demonstrating acidification of the soil, which if left unchecked will deplete the metal bioavailability, fertility, and microbiology of the soil to such an extent it will be inhospitable to crops in 25 to 30 years. The cause of this acidification is largely an increase in the application of N fertilizer, but also a result of the rapid industrialization of the county, which has led to greater numbers of factories, which spew industrial effluents that contribute to the rise of acidification. These nutrient imbalances in the soil resulting from incorrect application of fertilizer causes non-point pollution of N into the surrounding water bodies, endangering both human and ecosystem health.