Corn-soybean Rotation Research Articles

Nitrous Oxide Emission and Soil Carbon Sequestration from Herbaceous Perennial Biofuel Feedstocks

Core Ideas Adding N fertilizer increases N2O emission from perennial grasses managed as feedstock. Interseeding clover with perennial grasses reduced N2O emission and yield. Soil organic C storage under grasses may be inadequate to offset fertilizer‐induced N2O flux. Nitrogen management to optimize yield‐scaled N2O flux from established grasses is needed. No soil organic C storage occurred under no‐till corn–soybean rotation to offset N2O flux. Switchgrass (Panicum virgatum L.) and big bluestem (Andropogon gerdardii Vitman) are potential bioenergy feedstocks. Perennial grasses managed as bioenergy feedstock require nitrogenous inputs, which can cause N2O emission and, thereby, alter their effectiveness to mitigate greenhouse gas (GHG) emission. Few studies have measured N2O emission from perennial grasses managed as feedstock. The objectives of this study were to compare N2O flux and soil organic C (SOC) storage between (i) grasses with legume companion crops or with nitrogenous fertilizer, (ii) two grass harvest times (autumn and spring), and (iii) perennial systems and corn (Zea maize L.)–soybean [Glycine max (L.) Merr.] (C–S) rotation, all without tillage. Nitrous oxide flux was measured from May 2009 to May 2012, and SOC was measured in 2000, 2006, and 2011. Big bluestem–clover (Dalea) and switchgrass–clover treatments had dramatically reduced annual N2O emissions and yield‐scaled emissions compared with the respective grasses with urea fertilizer. Cumulative N2O emission was 14 to 40% greater in the big bluestem‐spring and switchgrass‐spring treatments compared with respective autumn‐harvested treatments. The average cumulative emission in fertilized big bluestem and switchgrass treatments (18.5 kg N2O‐N ha−1) exceeded that of the C–S rotation (12.7 kg N2O‐N ha−1). The emission factor (EF) for fertilized grasses averaged 2.5%, corn averaged 1.05%, and C–S rotation averaged 1.9%. The SOC storage by perennial grasses was limited to 0 to 5 cm and thus may not be adequate to offset N2O emission. Nitrogen management refinement is recommended for herbaceous perennials to optimize biomass production and minimize N2O emission.

Characterization of Pythium spp. Associated with Asymptomatic Soybean in Southeastern Pennsylvania

Soybean production in Pennsylvania has increased substantially over the past 20 years and is a highly valued field crop, together with corn. Soilborne pathogens such as Pythium spp. can contribute to soybean stand establishment issues, particularly under the conservation tillage practices that are common in the state. In this study, we collected soil samples from eight asymptomatic soybean-corn rotation fields across six counties in southeastern Pennsylvania between May and June 2012. Pythium spp. were isolated via baiting, and tested for aggressiveness on both soybean and corn using laboratory assays. In addition to our culture-based survey, we also assessed the use of cytochrome oxidase subunit 1 pyrosequencing as a culture-independent method for measuring Pythium spp. diversity from environmental samples. Diversity estimates were consistent between the culture-based and pyrosequencing datasets; however, important methodological biases inherent to culture-independent methods may have led to some differences. Our results show that several Pythium spp. previously characterized as soybean or corn pathogens are present in southeastern Pennsylvania, including Pythium irregulare, P. sylvaticum, and P. ultimum var. sporangiiferum, with isolates showing aggressive phenotypes in lab assays.

Improving resource-use-efficiency with no-till and crop diversity

AbstractRecently, we conducted a case study that showed a no-till, diverse cropping system increasing corn yields in a semiarid climate compared with a tilled, corn–soybean rotation. Further analysis showed that the no-till system improved resource-use-efficiency of corn; inputs were reduced 42% averaged across five resources. The largest reduction with inputs involved nitrogen fertilizer and fuel. Reduced fertilizer input was attributed to greater soil microbial activity. A surprising trend was that cost of weed management in corn was 45% lower in the no-till system, due to resistant weeds being present only in the tilled, corn–soybean system. Crop diversity in the no-till system suppressed development of weed resistance. Integrating a diversity of crops with no-till can improve efficient use of resources.

Soil chemical properties as influenced by long-term glyphosate-resistant corn and soybean production in the central Great Plains, USA

Glyphosate-resistant (GR) corn (Zea mays L) and soybean (Glycine max (L.) Merr.) production and glyphosate application could affect soil chemistry due to indirect effects on soil organic matter (SOM) and nutrient cycling. We determined soil chemical properties after 15-yr of glyphosate application, continuous GR corn (CC) and GR corn-soybean rotation (CS) under no-tillage. Herbicide treatments were 1) glyphosate at 0.42 and 2) 0.84kga.e.ha−1 each applied twice in all years, 3) an alternating treatment of glyphosate at 0.84kgha−1 applied twice followed the next year by a non-glyphosate herbicide treatment, and 4) a non-glyphosate herbicide treatment in all years. Results showed that crop rotation and soil sampling depth affected SOM, pH, and nutrient concentrations. Soil pH, exchangeable Ca and K concentrations at the soil surface were reduced with CC production. In contrast, SOM, Fe, Mn, NO3-N, SO4-S and soil P concentrations in the top 7.5cm of the soil increased with CC production. Glyphosate application affected concentrations of P, NO3-N, SO4-S and Fe but not pH, Ca, Mg, Mn or Zn. Findings of this long-term study showed that crop management practices including herbicide program and crop rotation could affect soil chemical properties but cropping systems with CC increased soil surface fertility compared to CS production.

Crop rotation and Raccoon River nitrate

Previous research predicted that the biofuel-driven expansion of corn (Zea mays L.) area would increase riverine export of nitrate-nitrogen (NO3-N) in the Mississippi River Basin. Accurate information about water quality trends in agricultural watersheds is needed to better inform agricultural policy and to help quantify the effectiveness of field and landscape management practices. This study was designed to (1) characterize possible NO3-N trends within the Raccoon River watershed (RRWS) of central Iowa, and (2) explore links between the relative areas planted to corn and soybean (Glycine max) and water quality. We examined NO3-N concentration and loading data from more than 60 main stem river and tributary locations in the RRWS for the period 1999 to 2014. In addition, we assessed the role of climate, crop rotations, and simplified annual N budgets on NO3-N concentrations and loads to show that expansion of corn area has not increased Raccoon River NO3-N levels. Nitrate-N concentrations have not increased as corn area increased 19% and fertilizer N inputs increased 24% since 1999. We conclude that expansion of corn area at the expense of soybean may be affecting water quality. Better management of soybean in a corn–soybean rotation should reduce NO3-N export from the watershed, and reducing throughput of water in this artificially drained system will improve water quality.

Determining the Role of Plant‐Parasitic Nematodes in the Corn–Soybean Crop Rotation Yield Effect Using Nematicide Application: II. Soybean

Corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] crop rotation is well‐known to increase yields of both crops and is called the rotation effect. This study was conducted to determine the role of plant‐parasitic nematodes—particularly soybean cyst nematode (SCN, Heterodera glycines),—in the rotation effect for soybean. Research was conducted at a site in Waseca, MN, that was established in 1982 to study corn–soybean rotation. Included in the study were treatments in 1 to 5 yr of SCN‐susceptible soybean monoculture following 5 yr of corn, continuous SCN‐susceptible soybean monoculture, and continuous soybean with SCN‐resistant cultivars since 2010. Granular nematicides have been applied to half of each plot since 2010 to minimize nematode populations across crop sequences as a way to determine the role of nematodes in the rotation effect. Because nematicide was similarly effective in each crop sequence, it was not effective for determining if SCN damage varied by crop sequence. Soybean cyst nematode populations increased (P ≤ 0.05) in soybean monoculture and were negatively correlated with soybean yield (P ≤ 0.05). Pratylenchus (lesion nematode) populations decreased significantly in soybean monoculture particularly when comparing first and second year in soybean (P ≤ 0.05). Helicotylenchus (spiral nematode) and Xiphinema (dagger nematode) populations were significantly decreased in continuous soybean compared to most sequences in 5 or fewer years of monoculture (P ≤ 0.05). Trends in nematode populations suggest SCN may have had a role in the rotation effect for soybean yield, but that Pratylenchus, Helicotylenchus, and Xiphinema did not. Growing soybean in monoculture decreases yield. Growing soybean in monoculture increases soybean cyst nematode populations. There was some evidence that soybean cyst nematode can be involved in monoculture yield decline for soybean.

Nongrowing season soil surface nitrate and phosphate dynamics in a corn–soybean rotation in eastern Canada: in situ evaluation using anionic exchange membranes

Determining how agricultural management practices affect changes in soil nitrogen (N) and phosphorus (P) could further our understanding of soil N and P cycle. The main objective of this study was to assess in situ nongrowing season soil nitrate and phosphate dynamics as adsorbed on anionic exchange membranes (AEM-N and AEM-P, respectively). The membranes were buried in the surface horizon (5 cm below the soil surface) over the nongrowing season (mid-November to mid-April) in five consecutive years (2009–2010 to 2013–2014) in a long-term corn–soybean rotation experiment established in 1992 in eastern Canada. The treatments consisted of two tillage systems, namely moldboard plow (MP) and no-till (NT), and nine combinations of fertilizer applications, namely three N rates (0, 80, and 160 kg N ha−1) and three P rates (0, 17.5, and 35 kg P ha−1) in a split-plot design with four replications. The results showed that AEM-N and AEM-P averaged 1.8 µg cm−2 d−1 and 7.4 ng cm−2 d−1 under MP, respectively, and 2.8 µg cm−2 d−1 and 67.8 ng cm−2 d−1 under NT, respectively. Nitrogen application increased AEM-N in 2010–2011, 2011–2012, and 2012–2013, but decreased AEM-P mainly under NT. Phosphorus fertilization had no effect on AEM-N, but increased AEM-P under both MP and NT. We conclude that AEM can be used as a technique to study N and P dynamics under cold winters of eastern Canada.

Eleven years of runoff and phosphorus losses from two fields with and without manure application, Iowa, USA

Monitoring runoff at field edges can show how cropping systems and conservation practices affect runoff hydrology and water quality. Multi-year records are needed to characterize these effects, because of the variable, ephemeral nature of rainfall-runoff events. This study compared runoff and phosphorus (P) losses from two fields in central Iowa from 2000 through 2010. Both fields were managed in the same three-year, corn (Zea mays L.)–corn–soybean (Glycine max (L.) Merr.) rotation, but one field received applications of swine manure for each year of corn. Results comprised 116 events at the manured site and 94 events at the non-manured site, with 74 events common to both locations. Rainfall-runoff relationships for the two fields were similar; annual runoff averaged 54mm from the non-manured field and 47mm from the manured field. Large storms (>60mm rainfall) comprised about 10% of the runoff events in both watersheds, producing 12–16% of the total P loads. Moderate storms (30–60mm rainfall) generated most (65–70%) of the P load from both watersheds. Losses of P averaged 1.8kg Pha−1year−1 from the manured watershed and 1.05kgPha−1year−1 from the non-manured watershed. Relationships between runoff-volumes and P-loads differed between the two watersheds (p<0.05). Results highlight the challenge of maintaining adequate soil P levels while minimizing runoff P losses under a corn–soybean rotation, but indicate conservation practices that can limit runoff from storms of 30–60mm of rainfall can help producers meet that challenge.

Influence of long-term corn–soybean crop sequences on soil ecology as indicated by the nematode community

In the Midwestern United States, corn–soybean rotation is an essential agricultural practice, but relatively little is known about the impact of different corn–soybean cropping sequences on soil ecology. A long-term research site in Waseca, Minnesota was established in 1982 to study corn–soybean rotation. At the site, various corn–soybean crop sequences can be compared each year including corn and soybean in 1 to 5 years of monoculture and continuous monoculture of each crop. Additionally, granular nematicides (terbufos or aldicarb) have been applied to half of each plot since 2010 to minimize nematode populations, particularly plant-parasitic nematodes, across crop sequences. The nematode community, a sensitive indicator of changes in soil ecology, was assessed at this site to determine the impact of corn–soybean crop sequences and nematicide application on the soil ecosystem. Nematicide application was effective against target nematodes, herbivores, but also impacted non-target nematodes and thus soil ecology. Nematicide application decreased fungivore and bacterivore populations, diversity, and maturity; but significantly increased enrichment compared to no nematicide application. The nematode community and thus soil ecology was significantly different in corn compared to soybean cropping systems and changed most during initial years after switching crops. Cropping systems in corn supported significantly greater fungivore populations, fungal decomposition pathways, more diversity, and a more mature ecosystem compared to soybean systems. Soybean systems supported significantly greater bacterivore populations and a more disturbed, enriched ecosystem. These differences between corn and soybean systems demonstrate that each crop has a distinct impact on the soil ecosystem.

Effect of crop type and season on nutrient leaching to tile drainage under a corn-soybean rotation

Subsurface tile drainage is a significant pathway for nitrogen (N) and phosphorus (P) transport from agricultural fields. The objective of this study was to evaluate N and P loss through tile drainage under corn (Zea mays L.) and soybean (Glycine max L.) production in a corn–soybean rotation typical of agricultural management across the eastern Corn Belt of the US Midwest. Differences in nutrient concentrations and loadings between crop type and between growing (GS) and nongrowing seasons (NGS) were assessed. From 2005 through 2012, discharge and water quality were monitored at three end-of-tile locations that had estimated contributing areas ranging from 7.7 to 14.9 ha (19.0 to 36.8 ac) in a headwater watershed in central Ohio, United States. Nitrate-N (NO3-N) and dissolved reactive P (DRP) were the primary (>75%) forms of N and P in drainage water. DRP concentration and loading was not significantly different between crop types, but differed significantly by season. Mean weekly DRP concentration (0.22 mg L−1 [0.22 ppm]) was greater during the GS, while mean weekly DRP load (0.010 kg ha−1 [0.009 lb ac−1]) was greater in the NGS. In comparison, NO3-N concentration and load was dependent on the interaction between crop type and season, with the greatest NO3-N concentration (17.1 mg L−1) observed during the GS under corn production. Differences in N and P loss to tile drains were attributed to the timing of nutrient application and differences in seasonal discharge. Practices such as cover crops and drainage water management that target nutrient transport in the NGS should be explored as a means to decrease annual N and P loads. Adherence to recommended 4R nutrient stewardship (right fertilizer source, right rate, right time, and right placement) practices should also help minimize nutrient leaching to tile drains under a corn–soybean rotation.

Impact of Crop Residue and Corn-soybean Rotation on the Survival of Fusarium virguliforme a Causal Agent of Sudden Death Syndrome of Soybean

Soybean sudden death syndrome (SDS), caused by Fusarium virguliforme, is an economically important soilborne disease and is a major risk to many soybean [Glycine max, (L.) Merr.] production regions worldwide. Two-year studies were conducted in a greenhouse and in fields to examine survival of the fungus in corn-soybean residues. Corn kernels consistently showed significantly (P<0.05) higher F. virguliforme colony-forming units per gram of dry soil (CFU/g) in a greenhouse and in field micro-plots compared to no additional residue added treatment (control). None of the soil samples from commercial fields in Iowa showed significant (P<0.05) difference in F. virguliforme CFU/g within year of sampling, but between years there were numerical differences but not statistically different in samples if the previous crop had been corn, compared with winter wheat or soybean. In Fusarium spp. not causing SDS, CFU/g were significantly (P<0.05) higher in micro-plots amended with six different corn-soybean residue treatments compared with the control in 2008, while in 2009, only corn stock spread on soil showed significant (P<0.05) difference over the control. Our results suggest that a clean corn harvest could reduce SDS risk by reducing colonization of corn kernels that supports survival of F. virguliforme, while a considerable corn loss during harvest could increase SDS risk.

Carbon Stocks in Compartments of Soil Organic Matter 31 Years after Substitution of Native Cerrado Vegetation by Agroecosystems

Changes in carbon stocks in different compartments of soil organic matter of a clayey Latossolo Vermelho Distrofico (Typic Haplustox), caused by the substitution of native savanna vegetation (cerrado sensu stricto) by agroecosystems, were assessed after 31 years of cultivation. Under native vegetation, a stock of 164.5 Mg ha-1 C was estimated in the 0.00-1.00 m layer. After 31 years of cultivation, these changes in soil C stocks were detected to a depth of 0.60 m. In the case of substitution of cerrado sensu stricto by no-tillage soybean-corn rotation, a reduction of at least 11 % of the soil C pools was observed. However, the adoption of no-tillage as an alternative to tillage with a moldboard plow (conventional system) reduced CO2 emissions by up to 12 %.

Phosphorus Modeling in Tile Drained Agricultural Systems Using APEX

Phosphorus (P) losses through tile drained systems in agricultural landscapes may be causing persistent eutrophication problems observed in surface water. The purpose of this paper is to evaluate the state of the science in the Agricultural Policy/Environmental extender (APEX) model related to surface and tile P transport. This was accomplished using data from a monitored corn-soybean rotation field in the St. Joseph River watershed, IN. The estimation of soluble phosphorus (SP) in surface runoff and tile flow in APEX includes a user defined linear (based on GLEAMS) and nonlinear (Langmuir) sorption option. The results suggest that the inclusion of the Langmuir isotherm improved (18%) SP sorption estimates in surface runoff during the corn year only when P inputs were added, whereas the linear method was more appropriate during the soybean year when no fertilizers were applied. Similarly, SP estimates in tile flow were improved (30%) when using the Langmuir option during the corn year, though the overall model performance predicting this variable were very poor. Modeling improvements of P partitioning processes in APEX can help predict more realistic outputs. Yet to achieve this in tile flow, water percolation processes need to be improved to reflect preferential flow conditions often found in long-term no-till fields and in soils with high clay content. Greater accuracy in the estimation of the effect of artificial drainage systems, common in the US Midwest, should result in the improved evaluation of agricultural conservation practices in order to examine strategies that could reduce P losses for water quality purposes.

Impact of glyphosate-resistant volunteer corn (Zea mays L.) density, control timing, and late-season emergence on yield of glyphosate-resistant soybean (Glycine max L.)

Glyphosate-resistant (GR) volunteer corn is a troublesome weed in soybean fields in a corn-soybean rotation as well as in corn fields in a continuous corn production system. The objectives of this study were to evaluate the impact of (1) different densities of GR volunteer corn on soybean yields, present as individual plants or clumps, controlled at fourth trifoliate (V4), sixth trifoliate (V6), or full flowering (R2) soybean growth stages, and (2) late-season volunteer corn emergence on soybean yields, after being controlled at different soybean growth stages. Field experiments were conducted in 2013 and 2014 under irrigated conditions in Clay County, Nebraska, and under rain-fed conditions in Lancaster County, Nebraska, USA. To maintain the desired number of isolated volunteer corn plants (1250, 2500, 5000, and 10,000 plants ha−1) and clumps (63, 125, 250, and 500 clumps ha−1), individual seeds and/or corn ears were hand-planted in each plot based on their respective target densities. Volunteer corn was controlled with applications of clethodim at V4, V6, or R2 soybean growth stages. Late-season volunteer corn emergence had no effect on soybean yield with volunteer corn densities and control timings at both locations in 2013 and 2014. During the first year of study at Clay County, volunteer corn densities and control timings had no effect on soybean yield. When volunteer corn was left uncontrolled or controlled at the R2 soybean growth stage, yield was the lowest at highest isolated volunteer corn plants (10,000 plants ha−1) plus clump density (500 clumps ha−1) during the second year of study in Clay County (≤5068 kg ha−1) and during both years of study in Lancaster County (≤1968 kg ha−1).

Long‐Term Corn and Soybean Response to Crop Rotation and Tillage

Long‐term experiments are essential to understand how crop rotation and tillage practices affect corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] production and its resiliency to variable weather conditions. A 28‐yr rainfed experiment was conducted in Nebraska to evaluate continuous corn (CC), the corn phase of corn–soybean rotation (CS), continuous soybean (SS), and the soybean phase of corn–soybean rotation (SC), and tillage system (chisel [CH], tandem disk [DK], moldboard plow [MP], no‐till [NT], ridge‐tillage [RT], and subsoil tillage [ST]) on grain yield and yield stability. In 19 of 28 yr, CS yields were greater than CC, although the corn grain yield advantage in CS decreased as CC yield increased. Rotated soybean (SC) grain yield was greater than SS in 67% of cropping years, and similar in the remaining 33%. Stability analysis showed that all crop rotation and tillage combinations, except CH for soybean, resulted in stable grain yields across a range of seasonal weather patterns. Corn grain yields were affected by tillage in 29% of the years, while NT soybean resulted in consistently high and stable grain yields following an initial 11‐yr lag period. We conclude that crop rotation has a greater impact on corn and soybean production than tillage in the western Corn Belt, although nearly all combinations can produce stable yields if well managed.

Improved Yield and Nitrogen Use Efficiency of Corn following Soybean in Irrigated Sandy Loams

Crop rotation influences yield through its effects on nutrient and pest cycles, soil C, water availability, and soil physical and chemical properties. A cropping system study was conducted from 2004 to 2008 near Brunswick, NE, on sandy loam (Haplustolls) soils to evaluate improvements of irrigated corn (Zea mays L.) yield and N use efficiency (NUE) when following soybean [Glycine max (L.) Merr.] in 2 yr as corn following soybean (CS) or in 3 yr as first-year corn following soybean (C1) and second-year corn following soybean (C2) compared with continuous corn (CC). SPAD readings at V10 and R2 were approximately 3 to 4% greater in CS than CC, indicating more in-season N availability. Corn grain yield of CS (12.1 Mg ha−1) was 20% greater than CC (10.1 Mg ha−1), with 69 and 57% greater NUE and N recovery efficiency, respectively. At zero N applied, corn harvest index was 15% greater in CS with 37% increased plant N uptake at harvest compared with CC. In CS, fertilizer replacement value estimated soybean N credits of 66 and 49 kg N ha−1 based on grain yield and plant N uptake, respectively. The difference in N rates needed to produce maximum grain yield of CS vs. CC was estimated at 32 kg ha−1 soybean N credit. The average soybean N credit was 49, 41, and 26 kg N ha−1 for the corn in CS, C1, and C2, respectively. Both the 2- and 3-yr corn–soybean rotations on loamy sand soils improved corn yield and NUE.

Comparison of Timing and Volume of Subsurface Drainage under Perennial Forage and Row Crops in a Tile-Drained Field in Iowa

<abstract> Subsurface drainage systems in Iowa increase the productivity of annual row crops, such as corn and soybeans, but also contribute to alterations in the hydrological balance of the region and leaching of nutrient pollutants, such as NO₃-N. This study‘s objective was to determine whether perennial forage orchardgrass can reduce the volume and change the timing of subsurface drainage in tiled fields in Iowa, thereby contributing to reductions in NO₃-N leaching and moderating changes in the hydrology. Research was conducted at Iowa State University‘s Agricultural Drainage Water Research Site, located in northwest Iowa. Six 0.05 ha plots (three control and three treatment plots), each including subsurface drainage with continuous flow monitoring, were planted to row crops (RC) consisting of either a corn-soybean rotation or continuous corn from 1990-2004 (the pretreatment period). During the treatment period (2006-2011), control plots remained in RC while treatment plots were planted to perennial forage (PF), a mixture of orchardgrass, red clover, and ladino clover, succeeding to a monoculture of orchardgrass. During the pretreatment period, control and treatment plots showed no difference in subsurface drainage. During the treatment period, over the entire drainage season (March to November), PF did not decrease subsurface drainage; however, during the month of May, PF decreased subsurface drainage by 32% (p < 0.05). Early spring, including May, is a critical period for drainage in Iowa, as wet field conditions and a lack of vegetative cover contribute to a majority of the drainage and leaching of NO₃-N from row crop fields during this period. Further research including different perennial species is needed, and investigations in different geographical regions are needed, as differences in precipitation and weather will affect the timing and volume of subsurface drainage.

Development of Corn Stover Biofuel: Impacts on Corn and Soybean Markets and Crop Rotation

What would be the impacts of a viable market for corn stover? A partial equilibrium model and a linear programing model were used to determine to what extent the existence of a viable market for corn stover would affect the traditional corn-soybean crop rotation in the US. We find that with government support production of biofuel from corn stover could significantly increase. That boosts profitability of farming corn in combination with harvesting corn stover versus soybeans. We show that if corn stover is demanded for biofuel, then a major shift will be observed in crop rotations in the US.

Crop yield and phosphorus uptake as affected by phosphorus-based swine manure application under long-term corn-soybean rotation

With increasing interest in adopting phosphorus (P)-based manure application, a good knowledge of manure form-specific agronomic performance is needed to assure crop productivity and to safeguard the environment. We evaluated the effects of three forms of swine manure (liquid, LM; solid, SM; and liquid manure compost, MC), each applied at 100 kg P ha−1 in every other year to the corn phase of a corn (Zea mays L.)-soybean (Glycine max L.) rotation, on crop yield, P uptake, and partial factor productivity of applied P (PFPP), compared with chemical fertilizer (CF) from 2004 to 2011 in a clay loam soil. The corn yield followed the order of LM > SM ≥ MC, while soybean yield did not differ amongst the three forms of swine manure. Similar patterns were observed for total P uptake and grain P removal for both corn and soybean. Manure P source agronomic coefficients calculated by dividing grain yield from the manure treatment by that from the CF treatment were 1.14, 0.85 and 0.74 for corn, and 1.00, 1.02 and 0.93 for soybean, for LM, SM, and MC, respectively. Compared with CF, the PFPP values for LM and SM were similar, but decreased by 26.3 % for MC, for corn. For soybean, the PFPP values increased linearly with year of cropping for CF and LM, while they remained unchanged over time for both SM and MC. Phosphorus-based manure application must be optimized on a form-specific basis with adoption of P source agronomic coefficients as a management tool to maximize P utilization efficiency.

Soybean Yield Response to Rhizobia Inoculant, Gypsum, Manganese Fertilizer, Insecticide, and Fungicide

From 2000 to 2013, soybean [Glycine max (L.) Merr] grain commodity price increased by almost 300% generating interest in inputs to maximize yield. The objective of this study was to evaluate the effect of commonly sold inputs on soybean grain yield in enhanced (high‐input) and traditional (low‐input) production systems. Inputs evaluated included: Rhizobia inoculant, gypsum, Mn fertilizer, insecticide, and fungicide. A 16 site‐year trial was established in Ohio during 2013 and 2014. Rhizobia inoculant was seed‐applied before planting, gypsum was applied at the VC growth stage (unrolled unifoliate leaves), and foliar Mn, insecticide, and fungicide were applied at the R3 growth stage (initial pod development). There was very little yield response associated with the inoculant, gypsum, Mn, and insecticide due to fields being in a corn–soybean rotation, no S deficiencies, limited Mn deficiencies, and limited insect defoliation. The omission of fungicide from the enhanced production system reduced yield in 5 of 16 site‐years by 0.21 to 0.79 Mg ha−1, but its addition to a traditional system increased yield significantly at 1 of 16 site‐years by 0.47 Mg ha−1. Across the 16 site‐years, soybean yield was influenced by fungicide application when fields had disease present, above average yield (&gt;3.5 Mg ha−1), and received &gt;25 cm of precipitation in June and July. The data indicate a very small potential for high‐input production systems to enhance crop yield without the presence of diseases, insects, or nutrient deficiencies.