Home / Programs / Research

Meta-analysis of Phosphorus Fertilizer Placement and Tillage Interaction for Corn and Soybean in the U.S.

IPNI-2014-USA-4RM09

Overview Related Article
01 Mar 2014

Project Description


Objectives
    1. Find, analyze, and summarize published and unpublished field-based data on corn and soybean response to P placement and the interaction with tillage.
    2. Complete a data review on yield response and phosphorus loses with surface runoff as affected by P placement and tillage interaction.
    3. Prepare and publish a refereed publication, in addition to extension materials including the main findings and providing a comprehensive summary of the work completed in this area in the region.
    4. Training of graduate students in applied soil fertility and nutrient management with a good understanding of both agronomic and environmental aspects of fertilizer placement under current production systems.

Introduction
Phosphorus placement and interactions with tillage has been evaluated extensively for corn and soybean in the US. Results suggest that placement of P fertilizer can play an important role in P plant uptake and yield as well as potential P loses to surface water. The rate of P uptake per unit of root in corn decreases throughout the vegetative growth phase (Mengel and Barber, 1974); and therefore early season P fertilizer applications and placement can be particularly important for optimum plant growth.

Broadcast application can result in a more uniform distribution and likely affecting more soil volume. Crops have shown a response in low soil test P (STP) conditions (Bordoli and Mallarino, 1998) and medium to high STP (Mallarino et al., 1991). However, accumulation of P near the soil surface may result in higher lost potential with runoff; and possible decreased P availability due to increased soil-fertilizer interaction in soils with high P sorption capacity. Broadcast application may be more practical for some producers and suitable for some soils and tillage conditions. However, soils and tillage conditions and the interaction with P application methods should be evaluated with larger datasets and across different soils and environments.

Strip-tillage aim to combine no tillage with conventional tillage so that residue is incorporated in a narrow band and soil is loosened for planting providing a good alternative for residue management. In the same pass, the addition of fertilizer in a deep band (6-8 in) with strip-till allows for concentrated nutrients directly below the seed. Reduced tillage systems have shown to positively impact soil water relationships by increasing the number of macropores and water infiltration, and therefore, likely reducing water runoff. When moisture is held in the topsoil in response to reduced tillage, uptake of P from the soil surface can be increased (Boomsma et al., 2007).

One advantage of deep band fertilizer application is the high concentration of nutrients below the plant with less fertilizer to soil contact. However, strip-tillage with deep banding creates an area of concentrated nutrients, creating a challenge for accurate soil sampling. Not only is it difficult to determine the location of the soil sample taken, but also the depth at which you collect (Bordoli and Mallarino, 1998). Farmers currently struggle with soil sampling accuracy in field where fertilizers have been applied in starter and deep bands without incorporation.

Potential P loses with water runoff can be affected significantly by phosphorus placement and tillage (Kimmell et al., 2001). Many studies in the US evaluated water runoff and P loses as affected by tillage and fertilizer. However studies often show different results, which may be due to differences in soils, rainfall amounts and intensities, slope, moisture content, and infiltration rate. Evaluation and summary of the existing literature can help to identify factors contributing to potential P loses in addition to tillage and fertilizer placement.

Crop response and P loss potential can be affected by the interaction between soil and tillage factors with P fertilizer placement. Accurate evaluation of these interactions would require large dataset that comprise a variety of soils, tillage and placement combinations. Meta-analysis is considered a quantitative systematic review of published and unpublished literature/datasets with the use of statistical methods (Philibert et al., 2012; Wang and Bushman, 1999). Meta-analysis can be more powerful than simple narrative reviews of a series of studies, because it summarizes data in a quantitative manner and makes it possible to assess the between-study variability (Doré et al., 2011). However, meta-analyses should be completed following sound methods and quality control (Philibert et al., 2012). Otherwise, there is a risk of biased estimations, misinterpretations and incorrect conclusions.

Some key components of meta-analyses suggested by several authors include: (1) Correct description of the bibliographic search procedures; (2) Listing of the references of the selected individual studies used in the meta-analysis; (3) Analysis of the variability of the results of individual studies, including estimation of variability between the selected individual studies and, when relevant, investigation of the sources of between-study variability; (4) Analysis of the sensitivity of the conclusions to any change in the dataset and/or in the statistical method used to analyze the data; (5) Assessment of the publication bias; (6) Data weighting. When the results reported in the individual studies differ in their levels of accuracy; (7) Availability of the dataset; and (8) Availability of the program used for statistical analysis (Borenstein et al., 2011; Gates, 2002; Roberts et al., 2006; Sutton et al., 2000; Wang and Bushman, 1999)

Procedure
This work will focus on two components (i) crop yield, and (ii) phosphorus lost assessment as affected by P placement methods and interaction with tillage. The methodology will involve a systematic review of published and unpublished research on phosphorus fertilizer placement under different tillage systems and diverse soils in the US. We will also search for data that may have not been summarized and published. Furthermore, we will summarize data from research that is being currently conducted when possible. The work will be developed using the steps described in the previous section, and with especial attention to the quality of the meta-analysis procedure to be used (Philibert et al., 2012). The following steps will be included:
    1. We will gather and review published and unpublished data on corn and soybean response with different P placement method under different tillage systems in the US with emphasis in the Midwest and Great Plains region. A database will be created including published studies from at least the last 30 years. Published journal articles will be search in the main databases (i.e. ScienceDirect, WileyInterScience, SpringerLink, and Web of Science) and the website of all the main agronomy and soil science journals.
    2. Select the published articles based on key criteria for quality of information and relevance. Some of these criteria will include: (1) Study should be completed in the US (Midwest or Great Plains Region) on corn and/or soybean; (2) Phosphorus source should be commercial fertilizer and information on fertilizer type should be provided; (3) the study should have an appropriate control, and soil test information provided; (4) the impact of fertilization and tillage on yields and/or P losses should be reported. Yield parameter and P runoff losses will be the main variables evaluated for this analysis; (5) response should be reported as means of treatments, and corresponding standard deviations and sample size reported in tables or graphs.
    3. The two response variables will be corn and soybean yield and P runoff losses. If the dataset include yield responses for several P rates, the yield will be used to study the relationship between yield and soil test P. Otherwise, for evaluation of overall effect, yields will be averaged for all P rates in the experiment.
    4. The response ratio will be estimated based on the ratio between the response variables (yield or P loses) from plots with P fertilizer to response from plots without P, and used to evaluate the effect of P fertilizer application under different application methods and tillage (Hedges et al., 1999). Data will be presented primarily as relative responses ([treatment-control)/control] × 100). Statistical analysis will be completed using MetaWin and SAS (Rosenberg et al., 2000; SAS Institute, 2010), and following methods described by (Wang and Bushman, 1999).
    5. In addition to the response ratio, non-linear functions will be used to describe crop response to soil and fertilizer P rates. A non-linear mixed effect model will be fitted (Pinheiro et al.) using the PROC NLMIXED procedure (Littell et al., 2006; SAS Institute, 2010). Relative grain yield will be described by the exponential Mitscherlich function as modified by (Klausner and Guest, 1981): y = A – B exp –Cx;
    6. Results from this meta-analysis will be included in one or two refereed publication. In addition, bulletins and PowerPoint slides will be generated for extension use.

Background and Key Personnel
The principal investigators have previous experience with meta-analysis statistical techniques for fertilizer research (Ruiz Diaz et al., 2012). This previous experience, combined with collaborations with faculty in the department of statistics at Kansas State University will ensure the quality of analysis and procedures. The PhD student on this project (Cristie Edwards) will be the lead author with close support from advisors (Ruiz Diaz and Mengel). Cristie started her graduate program in soil fertility recently (fall of 2013). Her dissertation topic is on “Phosphorus placement under minimal tillage systems” a project supported by the Phosphorus Fellowship Program (cooperative program between IPNI, and industry partners) ending in 2014. At this stage in her program, Cristie will be required to complete a detailed literature review on this topic. And she would be an excellent fit for this project considering her background, the topic, and the stage in her PhD program.

Justification and Expected Outcome
Producers often question which fertilizer placement is better for a specific tillage system. There has been multiple studies in the past evaluating this topic for both agronomic and environmental aspects. However, currently there are no quantitative summaries of the data available in the literature on this topic. A meta-analysis can provide a better representation of soils and conditions that can affect crop response and potential for P runoff losses. A combination of multiple studies across the region can contribute to a stronger data set and may reveal some factors that may require more attention and perhaps further research.