Project Description:
To increase the sustainability of Illinois soy and improve soybean growers’ profitability, this work will tailor the 4Rs of P for regional soybean production. In addition to the 4Rs of P for central-north and southern IL production conditions, N-free P options will be evaluated in two-year field trials to quantify yield, P use efficiency, economics, and water quality benefits. Results will be used to position Illinois soy at the forefront of reducing N losses while identifying region-specific agronomic P practices to support profitable soybean production. This will conclude this study with year 2 of 2.
Summary/Project Scope:
I. Proposal Description and Background
This project will provide fundamental information on the sustainability of Illinois soy by addressing economically effective usage of phosphorus (P) with co-benefits to water quality. The work will evaluate best management practices for P of timing, placement, source and rate to ensure efficient and thus economic P usage for soybean growers. Updating the 4Rs of P management – specifically for soybean, and specific to the distinct soil-climate conditions of central-north vs southern Illinois– is expected to identify options to increase the profitable use of P inputs while reducing off-field nitrogen (N) and P losses. This work will therefore provide updated and evidence-based recommendations on the 4Rs P management options for soybean growers in distinct regions of Illinois. The source, rate, timing and placement of P will be evaluated. Field-based evaluation of timing and placement of P to increase soybean use efficiency of these inputs, and adding P source options to growers’ management toolbox, stands to improve agronomic, economic and environmental outcomes of Illinois soybean production. By quantifying these benefits to water quality, this project will position our state’s soybean growers at the forefront of environmental stewardship as active contributors to water quality improvement. This proposal therefore addresses “Farmer Profitability – Optimize farmer profitability through strategic farm management, yield and sustainable production practices.” Specifically, this proposal will “Provide actionable information through research, events and online resources to support soybean yield and profitability in Illinois” and “Encourage adoption of sustainable and profitable soybean production and nutrient management practices by Illinois soybean producers.”
(i) Problem
Increasing P efficiency for soybean
Managing P nutrition for soybean is critical since this leguminous species is self-sufficient in meeting the majority of its N needs. Additionally, the high nutrient density of soybean grain means that soybean translocates a high proportion of its total P taken into the grain (over 80%). Soybean has a higher P harvest index than corn1, 2, which is why replenishing P removed by harvest of soybean is an important practice for sustaining soybean yields. As soybean yields have increased, total P uptake has concurrently increased. Thus, in contrast to some other grains in which yield gains dilute the same amount of P taken up, higher yielding soybeans necessitates a corresponding increase in how much P is added and how efficiently it is used to support yields.
Currently, the 4Rs of P for are well recognized but relatively under-evaluated for soybean-specific management. For example, a common practice in Illinois is the application of P at the beginning of the corn phase of a corn-soybean rotation, but this practice may limit soybean yields. Targeting P inputs to the soybean phase of the rotation can increase soybean yields3, and specifically in-season P application4. Even in conditions where in-season P fertilization may not necessarily be cost-effective for soybean, there is still reason to consider a P-only source out-of-season: avoiding loss of N added via ammonium phosphate (MAP or DAP) is limited. Precision management of P is enabled by P-only sources that do not require inputs of N to entail P inputs, or vice versa.
Co-benefits for water quality
The common practice in Illinois of applying P at the beginning of the corn phase of a corn-soybean rotation may not only limit soybean yields, it may also encumber economic costs to growers in the form of nutrients exiting the field. These off-farm losses of N and P also have implications for water quality. Illinois is the largest state contributor of P to the Mississippi River watershed (13% of total), and a close second for N losses. Following a federal EPA mandate on N and P loss mitigation for states in the Mississippi River watershed, in 2015 the Nutrient Loss Reduction Strategy (NLRS) was developed by Illinois stakeholders to decrease by 45% the total N from Illinois to the Mississippi River.
A persistent challenge to reducing N losses is hidden in its co-addition in the dominant P sources in Midwestern agriculture: ammonium phosphates. Small changes in P management mean that Illinois soy is uniquely positioned to contribute to N loss reductions without compromising profitability. By decoupling inputs of N and P, mononutrient P sources such as triple superphosphate (TSP; 0-46-0) stand to deliver on soybean P needs without the need to supply additional N, which does not generally increase soybean yields but does pose a water quality risk. In years with wet and warm winters and/or springs, fall-applied MAP (11-52-0) or DAP (18-46-0) undergo substantial nitrification ammonium and subsequent losses by nitrate leaching and/or denitrification. On average, two-thirds of the N from fall-applied MAP or DAP may be unrecovered by crops and lost off-field5. Though agronomic this may correspond to a relatively low amount of N and thus expense, these risked N losses can be substantial for water quality. Averting this N loss by changing timing and/or source of P in soybean production could be a significant contribution to the Illinois NLRS.
(ii) Evidence for project need
This work will provide evidence-based recommendations on P management options for soybean growers to increase efficiency of P inputs. The Illinois Agronomy Handbook employs potentially outdated (pre-2000) soil test P recommendations that have not been specifically calibrated for soybean. Evaluating the timing, placement, source, and rate of P will provide needed updates to the Handbook, for the major soil types of the unglaciated south and glaciated north-central regions of Illinois. These P recommendations can further vary by timing and placement, including the potential of banding to increase soybean P use efficiency. Field-based evaluation of timing and placement of P to increase soybean P use efficiency of these inputs, and adding P source options to growers’ management toolbox, stands to improve agronomic, economic and environmental outcomes of Illinois soy. While these practices are broadly recognized, they are under-evaluated for their potential to increase P use efficiency for soybean specifically.
Non-ammoniacal P sources – superphosphates – were once the dominant P source in Illinois9-12 but now constitute 11% of P fertilizer sales in the state8. For much of the 20th century, single superphosphate (SSP; 0-20-0) or TSP (0-46-0) were the dominant P source in Illinois. University of Illinois field trials through the 1990s evaluated superphosphate as the P source14, and the Illinois Agronomy Handbook listed SSP as the P source of choice through the 1970s15 and TSP as the P source of choice in the 1980 edition16. With recent re-introduction of TSP into the North American market at competitive pricing with ammonium phosphates (e.g., The OCP Group) and increased interest by growers, there is growing interest in and sources of N-free P in Illinois.
In addition to increasing agronomic use efficiency of P inputs, updating the R4s of P management specifically for Illinois soybean –including the right source – stands to deliver water quality benefits. The change in P source, but not necessarily P rate, and the similar pricing of MAP and DAP as TSP per unit P means that adding N-free P options to producers’ nutrient management toolbox stands to maintain producer profitability while improving environmental outcomes of agriculture in Illinois.
Field-based data on how crop production practices can mitigate nutrient losses is useful to demonstrate how the agricultural sector and growers are key leaders in environmentally responsible nutrient management. In particular, this can be achieved by yield-scaled assessments: evaluating nutrient losses with respect to crop productivity6. The yield-scaled metric agronomically contextualizes the impacts of nutrient management practices on nutrient loss mitigation, and can form the basis for the N or P footprint of a given crop – a key metric of sustainability. However, only one study in Illinois has evaluated yield-scaled N leaching for corn at one location7, and no studies to have evaluated yield-scaled N loss mitigation for soybean, despite the strong potential to achieve appreciable N loss reductions in by managing P sources in soybean production.
(iii) Return on mission (ROM) for Illinois soybean growers and industry
Land grant institutions, growers, and commodity boards can and should work together to get ahead of potential regulations by providing evidence-based evaluation of environmental impacts and best practices in the agricultural sector. By identifying practices that co-deliver yield, profitability and water quality benefits, this work will position ISA and our state’s soybean growers at the front of environmental stewardship. This project will provide specific recommendations on which P management practices enable synergistic yield, profitability and environmental outcomes. Using information on yield and economics of P sources, timing and placement, soybean growers can make informed decision making on cost-effective P management that includes options for reducing N losses. Finally, increased efficiency of P usage by evaluating timing, placement, source and rate for soybean stands to improve profitability of growers, with the added benefit of keeping more P for the crop and out of our state’s water bodies. These outcomes mean that the investment of ISA dollars will support grower profitability while simultaneously optimizing strategies and providing evidence for the sustainability of Illinois soy. In particular, the hypothesized benefit of using N-free P sources mean that Illinois soy can be a leader in reducing N losses in the state and the Mississippi River Basin.
(iv). For proposals that build on past ISA funding, explain the value of continuing the project and include examples of past successes.
There is no past ISA funding to report for this PI.