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Sap flow gages are used to estimate plant transpiration (an indirect form of soil water loss), but relatively few studies compare transpiration with other measures of soil water loss. The purpose of this study was to compare two landscape positions for transpiration (T) from sap flow measurements, soil water changes estimated by daily neutron probe readings, and evapotranspiration (ET) determined via eddy covariance and associated microclimate measurements. Monitoring at backslope and toeslope positions occurred for 2 wk during the corn (Zea maysL.) early reproductive stage. Evaporation from soil (E) and potential ET were calculated from microclimate measurements. The T from sap flow measurements plus calculated soil E was significantly higher at the backslope position than the toeslope position. Grain yields were within 3% (9020 vs. 8774 kg ha−1) for the toeslope and backslope positions. At the backslope position, crop development was delayed at the milk stage and leaf area index was larger compared with corn at the toeslope position. For July 18th through August 4th, the water table was 0.65 to 0.85 m deep at the toeslope position but 1.70 to 2.28 m deep at the backslope position. Higher water table depths at the toeslope position would supply extra water during dry times compared with the backslope position but could also have caused low temperature stress early in the season. The backslope faced south and could have experienced higher wind speed causing water stress during dry periods. The mid to late 2011 growing season was dry enough to detect landscape position effects.

Corn (Zea maysL.) stover has been identified as an important feedstock for biofuel production but its removal will likely increase soil erosion. To address this issue 35 species of grasses and legumes were evaluated as potential perennial ground covers (PGCs) in corn. Selection of species encompassed both C3 and C4 species with a wide range of developmental and morphological features. The objectives were to (i) identify species that could support a high level of corn production while requiring minimal management and (ii) identify morphological traits and growth habits of suitable entries as PGC. Over the 3‐yr study period species with slow growing and spreading habits were more conducive to corn production, even though these PGCs still caused an average 23% reduction in corn grain yield. Meadow fescue (Festuca pratensisHuds.), sheep fescue (Festuca ovinaL.), Canada bluegrass (Poa compressaL.), fowl bluegrass (Poa palustrisL.), and colonial bentgrass (Agrostis capillarisL.) were identified as suitable PGC species. These species were generally shorter and slower to spread into the corn rows compared with other, more aggressive species. Based on these observations an ideotype for future PGC species should be low growing, clump forming, and shade tolerant and have delayed green‐up in the spring.

Constraints to maize (Zea maysL.) stover biomass harvest may be mitigated by using a living mulch (LM) to offset C exports and control soil erosion. Living mulches can compete with the main crop for resources. The objective of this research was to quantify competitive effects of LM management systems grown in continuous maize with stover removal. Maize was planted into creeping red fescue (CF) (Festuca rubraL.), Kentucky bluegrass (KB) (Poa pratensisL.), and a mixture of CF and white clover (Trifolium repensL.) (MX) LMs in 2008, 2009, and 2010 near Ames, IA. Management treatments were fall strip‐tillage (ST) and no‐tillage (NT), with either a pre‐planting paraquat burn‐down followed by two glyphosate bands (PQ) or glyphosate bands only (GLY). Kentucky bluegrass PQ ST produced similar grain yields (11,230 kg ha−1) all 3 yr as the no LM control (11,810 kg ha−1) with a harvest index (HI) of 0.55 compared to 0.52 in the control, averaged across years. The control produced greater stover dry matter (SDM) (10,110 kg ha−1) 2 of the 3 yr compared to KB PQ ST (8600 kg ha−1). Total groundcover averaged 80% in KB PQ ST compared to only 45% in the no LM control. These results indicate that a combination of herbicide suppression and ST suppresses LMs adequately to maintain competitive maize grain yields. Additional research under varying climatic conditions will further quantify the risk of LM management systems to increase the sustainable stover harvest of maize biomass feedstocks.

Developing robust relationships between dry matter (DM) and plant number (PN) in interseeded red clover (Trifolium pratenseL.) and winter cereal systems are useful for predicting potential DM. Predicting DM months in advance enhances producers’ ability to determine forage requirements. Data from five winter cereal and red clover studies conducted during the period 2003 to 2009 were synthesized to develop robust relationships between red clover DM and PN using treatments that included different winter cereal species and variety, winter cereal seeding rate, red clover variety, tillage, and soil amendment. Dry matter data were collected during two 40‐d harvests after winter cereal harvest. The relationship between red clover PN and DM was described mathematically by a two‐phase regression for both harvests following winter cereal harvest. During the first harvest, the relationship was described by a parabola in the first line segment while the second line segment had no slope. In the second harvest, the first line segment was a simple positive linear relationship and the second line segment also had no slope. The join point for the first harvest occurred at 90.3 plants m−2while the second harvest join point occurred at 42.3 plants m−2. Red clover PN above 80 plants m−2likely provide around 90% of total maximum DM while red clover PN around 50 plants m−2likely only provides about 70% of total maximum DM.

Soluble organic matter (OM) is a small but very mobile and reactive fraction of soil organic matter (SOM). We characterized the properties of soluble OM from 0‐ to 125‐cm soil depth in maize (Zea maysL.)‐based agricultural systems that were managed with conventional tillage (CT) and no‐tillage (NT) for 23 yr. Water‐extractable organic matter (WEOM) and salt‐extractable organic matter (SEOM) were obtained in a sequential extraction procedure using dilute (0.01M CaCl2) and concentrated (0.5 M K2SO4) salt solutions. Subsequently, WEOM and SEOM were characterized using resin fractionation, specific ultraviolet absorption at 254 nm (SUVA254) and humification indices (HI). Concentrations of C and N of SOM and SEOM and C of WEOM declined with increasing soil depth. In contrast to less pronounced differences in C and N of SEOM in CT and NT soils, those of WEOM were greater (52–116% for C and 26–86% for N) in NT than CT soils throughout the soil profile. The proportion of C and N in SOM recovered as WEOM and SEOM increased with soil depth (three to nine times for C and two to five times for N). The proportion of hydrophilic‐C increased with soil depth, but the proportion of humified OM decreased with soil depth. Consistent with reports that indicate CT enhances OM decomposition, our data suggest WEOM and particularly SEOM fractions in CT soils are more decomposed than NT soils down to 125‐cm depth. The relative pool size and properties of WEOM and SEOM demonstrated a higher in situ contribution of SOM to soluble OM pool with increasing soil depth.

Frost‐seeding red clover (Trifolium pratenseL.) into winter cereals is an efficient establishment method, although performance under contrasting soil management practices remains unclear. Wheat and intercropped red clover productivity were evaluated in intensive tillage (IT), moderate tillage (MT), and no tillage (NT) with and without compost amendment in a corn (Zea maysL.)–soybean [Glycine max(L.) Merr.]–winter wheat (Triticum aestivumL.) and red clover rotation between 2005 and 2010. Wheat yields were not affected by tillage system and averaged 3.80 Mg ha−1but were 10% higher in compost amended soil compared to no compost. Red clover plant density and dry matter (DM) at cereal grain harvest averaged 127 plants m−2and 32 g m−2and were not affected by tillage or amendment treatments. Maximum wheat canopy light interception was attained in late May to early June and ranged from 84 to 91% and typically exceeded 77% light interception for at least 22 d. Red clover root DM increased on average 378% between wheat harvest and 40 d after harvest compared with a 64% average increase in red clover root length. Red clover shoot:root averaged 8.5 at wheat harvest compared with 11.2 40 d after wheat harvest. Producers using this wheat and red clover intercrop should expect no difference in wheat yield or red clover productivity when using IT, MT, or NT.

Constraints to maize (Zea maysL.) stover biomass harvest may be mitigated by using a living mulch (LM) to offset C exports and control soil erosion. Living mulches can compete with the main crop for resources, particularly water. The objectives of this research were to quantify soil water dynamics and maize water use in continuous maize with stover removal. Continuous soil water content (SWC) and reproductive whole‐plant water use were measured in no‐till maize growing in LMs of creeping red fescue (CF) (Festuca rubraL.), Kentucky bluegrass (KB) (Poa pratensisL.), and a no‐LM control between 2008 and 2010 near Ames, IA. In 2 yr with excessive rainfall (2008 and 2010), LMs increased SWC compared to the control at 15 cm. No‐till LM treatments lowered grain yield in 2008 and 2010 compared to the control, although a KB fall strip‐till treatment, which was part of the larger research study, produced yields that were not different than the control all 3 yr. Reproductive water use efficiency for no‐till KB in 2008 and 2009 (51 and 42 g grain per cm water) was 21 and 14% greater than the control (42 and 37) but 24% lower in 2010 (41 vs. 51). Maize water use in the control exhibited a bimodal response averaged across the 3 yr with peak water use occurring at the R1 through R2 period (0.58 cm d−1) and declining to 0.26 cm d−1during R5 through R6. In contrast, no‐till KB exhibited a simple negative linear relationship with water use rates declining from a high of 0.47 cm d−1during the R1 through R2 period to 0.22 cm d−1during R5 through R6. These results indicate LMs may increase SWC and utilize water more effectively, particularly when combining strip‐till and herbicide management.

Interseeding red clover (Trifolium pratenseL.) or alfalfa (Medicago sativaL.) into winter cereals in the North Central United States can provide forage and a green manure crop. We hypothesized that winter cereal canopy traits such as leaf area index (LAI) and whole plant dry matter (DM) would influence interseeded legume establishment and productivity, yet the effect of canopy traits on resource competition in intercropping systems is not well understood. This study was conducted from 2005 to 2007 to evaluate the impact of diverse cereal canopy traits on the establishment of frost‐seeded legume intercrops. In March, red clover and alfalfa were frost‐seeded into three winter wheat (Triticum aestivumL.) and three triticale (X TriticosecaleWittmack) varieties selected for differences in maximum LAI, plant height, and DM. Across three growing seasons, the cereals produced a range of LAI from 2.1 to 6.2 and whole plant harvest DM of 817 to 2029 g m−2. In the 2 yr with legume data, densities were influenced by cereal 1 yr and DM was affected by cereal both years. Alfalfa and red clover densities were similar, yet DM production was 42% higher in red clover 40 d after grain harvest. The presence of a legume intercrop did not affect grain yield, but reduced weed densities and weed DM 40 d after harvest. Producers implementing this intercrop may select cereal varieties based on grain yield, but must be cautious of varieties known to produce above normal LAI values because of the potential to reduce legume productivity.

Developing self‐seeding cover crop systems that minimize interspecific competition with soybean [Glycine max(L.) Merr.] are possible if cover crop growth is restricted to optimize cover crop seed production and dispersal. The objectives of this research were to quantify cover crop seed production, viability, and self‐seeding when growing concurrently with soybean. Winter wheat (Triticum aestivumL.), triticale (X TriticosecaleWittmack), and rye (Secale cerealeL.) were seeded at two target rates (99 and 198 seeds m−2). Three seed dispersal methods (natural seed rain, simulated combine, and mechanical preharvest) were also tested to disperse mature cover crop seed. Wheat combined with mechanical seed dispersal before soybean harvest exhibited the greatest consistency in self‐seeding (171 and 123 plants m−2in 2007 and 2008) regardless of establishment seeding rate. Additionally, wheat averaged 51 and 32% green groundcover in the fall of 2007 and 2008. Wheat seed viability (>82%) exceeded rye and triticale at soybean harvest, approximately 60 to 80 d after seed maturity. Cover crop species or establishment seeding rate did not affect soybean seed yield either year. Averaged across seeding rate and seed dispersal treatments, wheat self‐seeding systems exhibit the greatest potential for adoption, although soybean yield was 27% lower in 1 of 2 yr compared with a no cover crop control.

Early planting (late April to early May) is recommended for increasing soybean [Glycine max(L.) Merr.] yield but a full understanding of the physiological response is lacking. Carbon dioxide exchange rate (CER) was measured on soybean planted between 18 April and 29 May to determine if CER could resolve this yield difference. During the season CER was measured twice weekly on individual leaves. Total carbon fixation, dry matter accumulation, and radiation use efficiency (RUE) were calculated for the growth periods R1 to R3 and R3 to R6. During the early vegetative stages CER (before flowering) declined for all planting dates and reached a minimum of 0.566 (late planting) to 0.629 (optimal planting) mg CO2m−2s−1by approximately R2 (late flowering) followed by a linear rate increase to a maximum of 1.23 mg CO2m−2s−1by R5 to R6 (early seed fill). The optimal first week of May planting increased main‐stem node number, average CER during R1 to R6, total carbon fixation, and dry matter but did not increase seed yield. Overall, yield and seed number were positively related to CER between R3 and R6. These data demonstrate that (i) CER was controlled by plant growth stage and was independent of the date that growth stage occurred and (ii) early planting did not consistently increase the CER rate during the R3 to R6 growth stage, limiting yield improvement. Factors other than CER are more likely to explain the reported positive yield response to early planting.

Productivity rather than profitability is often used to compare agronomic systems. The objective of this study was to compare profitability of moldboard plow, chisel plow, and no‐tillage with or without composted animal manure in a corn (Zea maysL.)–soybean [Glycine max(L.) Merr.]–wheat (Triticum aestivumL.)/clover (Trifoliumspp.) rotation during three rotation cycles. Corn and soybean grain and seed yield exhibited a tillage × compost amendment interaction. Yield in moldboard and chisel plow with or without compost was similar, but yield in no‐tillage with compost was 8 and 5% greater than without compost for corn and soybean. Wheat yielded 5% higher in moldboard and chisel plow than no‐tillage and 4% higher in compost than no‐compost amendment. Wheat returns were similar among tillage and 7% higher when compost was amended. Corn production with or without compost amendment had similar returns in moldboard plow. Corn in chisel plow with compost had 8% greater returns than the no‐compost treatment. Corn in no‐tillage with compost had 15% greater returns with compost amendment than without. Similar corn returns were generated for all tillage systems if compost was applied. Soybean production using no‐tillage had 9% greater returns than without compost and greater returns than moldboard and chisel plow with or without compost. Summing returns across the three‐crop rotation indicated cycling nutrients through compost application exhibits a functional synergy in no‐tillage and chisel plow but not moldboard plow for these crops, which enhances their profitability.

Living mulches can function to supply forage in multifunctional cropping systems. Information quantifying nutritive value of forage plants in living mulch cropping systems is limited. The objective of this research was to quantify the nutritive value of forages from different plant functional groups managed as living mulches in 2 of 3 yr and as a forage crop in the third year of this 3‐yr corn (Zea maysL.)‐soybean [Glycine max(L.) Merr.]‐forage rotation. Alfalfa (Medicago sativaL.), Kura clover (Trifolium ambiguumM. Bieb.), and birdsfoot trefoil (Lotus corniculatusL.) were evaluated in sole seedings and binary mixtures, reed canarygrass (Phalaris arundinaceaL.) and orchardgrass (Dactylis glomerataL.) were included in three‐way mixtures, and a nondormant alfalfa was seeded each spring for comparison as a control. Average crude protein (CP) and neutral detergent fiber (NDF) during 2005, 2006, and 2007 was 190 and 449 g kg−1for Kura + alfalfa + reed canarygrass compared with 182 and 458 g kg−1averaged across birdsfoot trefoil + alfalfa + orchardgrass and Kura + alfalfa + orchardgrass mixtures, 195 and 397 g kg−1averaged across alfalfa, Kura + alfalfa, and alfalfa + birdsfoot trefoil, and 193 and 404 g kg−1for the nondormant alfalfa treatment. Weed densities averaged 104, 178, and 116 weeds m−2in 2005, 2006, and 2007 among living mulch treatments compared with 14, 84, and 67 weeds m−2in the nondormant alfalfa. Despite high weed densities in the living mulch treatments, no specific treatment effect was detected for nutritive value. All of these living mulch treatments produced high nutritive value forage.

Managing forages as living mulches during row crop production requires suppressing the forages to produce economical crop yields. The objective of this research was to identify forage plants with varied growth habit, persistence, and yield potential to provide desirable ecosystem functions in a multifunctional cropping system. Alfalfa (Medicago sativaL.), kura clover (Trifolium ambiguumBieb.), and birdsfoot trefoil (Lotus corniculatusL.) were evaluated in sole seedings, binary mixtures, and reed canarygrass (Phalaris arundinaceaL.) and orchardgrass (Dactylis glomerataL.) were included in three‐way mixtures in a corn (Zea maysL.)–soybean [Glycine max(L.) Merr.]–forage rotation. The forages functioned as cover crops in corn and soybean and were suppressed using a 25‐cm glyphosate band over the row. In the forage year, treatments containing alfalfa produced the highest yields (7824 kg ha−1average dry matter 2005–2007). Three‐way mixtures provided greater weed suppression in the interrow than sole seedings or binary mixtures in 2 of 3 yr (80 vs. 127 weeds m−2, 2005–2006 average). Kura clover provided greater weed suppression than alfalfa in the former row (108 vs. 186 weeds m−2). Reed canarygrass exhibited better stability in sward composition (20% in 2005 and 22% in 2007) than orchardgrass (58% in 2005 and 16% in 2007). Consequently, the best combination of species to use as living mulches to provide high forage yields and lower weed densities includes alfalfa, kura clover, and reed canarygrass. Seeding a nondormant alfalfa in the spring of the forage year will supplement yield and suppress weeds in the former crop row.

Coupling winter small grain cover crops (CC) with liquid manure injection may increase manure nutrient capture. The objectives of this research were to quantify manure injection effects using target swine (Sus scrofa) manure N rates of 112, 224, and 336 kg N ha−1on CC plant density, fall and spring shoot biomass, N, P, and K uptake and subsequent corn (Zea maysL.) yield. A winter rye (Secale cerealeL.)–oat (Avena sativaL.) CC was established before fall manure injection. Manure injection lowered mean CC plant density 25% because of CC mortality in the injection zone. Fall CC dry matter (DM) was 26% lower in the manure treatments than the no manure CC control, although no difference was detected for N (9.4 kg ha−1) or P (1.4 kg ha−1) uptake. No difference was detected for spring DM between CC no manure and manure treatments. Shoot DM, N, P, and K uptake increased 29, 41, 31, and 25% from the CC manure 112 to CC manure 224 with no increase above CC manure 224. Cover crop N uptake was higher in CC manure vs. no manure (60.1 vs. 35.6 kg ha−1). Cover crop P and K uptake were also higher in CC manure vs. no manure (9.2 vs. 6.6 kg P ha−1and 41.3 vs. 30.0 kg K ha−1). Corn grain yield was unaffected by CC and responded positively to manure application (11,022 with manure vs. 9,845 kg ha−1without manure). Coupling manure injection and cover crops can increase nutrient capture without lowering corn yield.

Triticale (×TriticosecaleWittmack) has potential as a feed crop in the north central United States and could also function as a companion crop for alfalfa (Medicago sativaL.) establishment. The objectives of this research were to assess the suitability of a short-statured spring triticale as a companion crop and determine optimum triticale seeding rates for grain yield and alfalfa establishment. Spring triticale ‘Trimark 37812’ and alfalfa were grown in companion at Ames and Sioux Center, IA during 2004 and 2005. Triticale was seeded at 198, 297, 396, 495, and 594 pure live seeds (PLS) m-2and alfalfa was seeded at 600 PLS m-2. The grain yield response to changes in stand density was quadratic with maximum yield occurring at 516 plants m-2. A plant density of 325 plants m-2and a seeding rate of 374 seeds m-2resulted in maximum profit. The grain yield at the stand density for maximum profit was 4.4 Mg ha-1. Increasing the triticale seeding rate had no effect on alfalfa stand density or dry matter yield. Alfalfa stand densities exceeded the 130 plants m-2threshold required for maximum long-term productivity suggesting the short-statured spring triticale cultivar used in this study was well suited for companion cropping with alfalfa.

Plant response to organic amendment often varies and may interact with tillage. The objectives of this research were to determine if soybean [Glycine max(L.) Merr.] growth, nutrient uptake, and soil water use could explain whole-plant and seed yield responses to tillage and compost amendment. A corn (Zea maysL.)-soybean-wheat (Triticum aestivumL.)/clover (Trifoliumspp.) rotation, with or without fall compost application was initiated in 1998 in plots that had been managed with moldboard plow (MP), chisel plow (CT), or no-tillage (NT) since 1988. No tillage by amendment interaction for yield was detected. Yield was similar in MP and CT. In 2003, yield was similar among tillage systems, but NT yielded 15% greater than MP and CT in 2004 and 8% lower in 2005. Mean yield across the 3 yr was similar. Compost amendment increased yield (9%) compared with nonamended soil only in 2004. Mean yield was 2% higher with compost than without. Water depth from the 0 to 90 cm soil depth was not affected by tillage or amendment. Seed P and K uptake were 18 and 16% greater in NT compared with MP and CT and 16 and 13% greater with compost than without in 2004. Soybean growing on compost-amended soil had less seed protein compared with nonamended soil. Alternatively, seed oil content was 2 and 1% lower in nonamended than amended soil in 2003 and 2004. The mechanisms responsible for compost-enhanced plant growth are difficult to quantify in the field under natural conditions because effects are short-lived or too extreme.

Regional‐level recurring spatial patterns of yield variability are important for commercial activities, strategic agricultural planning, and public policy, but little is known about the factors contributing to their formation. An important step to improve our understanding is recognizing regional spatial patterns of yield variability in association with regional environmental characteristics. We examined the spatial distribution of county‐level mean yields and CVs of mean yields of four functionally different crops—corn (Zea maysL.), soybean [Glycine max(L.) Merr.], alfalfa (Medicago sativa), and oat (Avena sativaL.)—in Iowa using Moran's Index of spatial autocorrelation. Patterns of association with 12 county‐level climatic, edaphic, and topographic environmental characteristics were examined using partial least squares regression. Two distinct geographic provinces of yield stability were identified: one in the northern two‐thirds of the state characterized by high mean yields and high yield constancy, and one in the southern third of the state characterized by low mean yields and low yield constancy. Among eight partial least squares regression models, which explained 50 to 81% of variation of mean yields and yield CVs, mean organic matter and mean depth to seasonally high water table had greatest relative importance to mean yields of grass crops and legume crops, respectively. Among the CV models, variables describing water availability were of greatest relative importance, with less distinct differences between grass and legume crops. Partial least squares regression is a potentially powerful tool for understanding regional yield variability.

Perpetuating cereal cover crops through self‐seeding may increase adoption by reducing risk and cost. Winter rye (Secale cerealeL.), wheat (Triticum aestivumL.), and triticale (× TriticosecaleWittmack) were used to develop self‐seeding cover crop systems in a soybean [Glycine max(L.) Merr.]–corn (Zea maysL.) rotation. Cereals were planted and managed chemically and mechanically in varying configurations. The objectives were to (i) quantify temporal establishment patterns after one cycle of self‐seeding, (ii) quantify shoot biomass, N uptake, and seed production growing concurrently with corn, and (iii) quantify cover crop establishment after two cycles of self‐seeding. Final plant densities for most species by treatment combinations were fully established within 1 wk after soybean (Cycle 1) harvest. Fall green ground cover after soybean was consistently higher with wheat and ranged from 16 to 61%. Straw biomass the following July ranged from 50.4 to 79.1 g m−2in wheat, 20.1 to 39.3 g m−2in triticale, and 0.0 to 52.7 g m−2in rye. Combined spring and maturity maximum N uptake was 20.7, 21.2, and 35.0 kg ha−1for triticale, wheat, and rye. Cycle two cover crop seed production was greatest in wheat and ranged from 559 to 1280 seeds m−2. Wheat also consistently had greater self‐seeding plant establishment after two cycles than rye and triticale, which ranged from 5 to 21% of the original plant densities and 19 to 64% of the cycle one plant densities. Future research on self‐seeding cereal cover crops should focus on efficient technologies for seed dispersal.

Perpetuating cereal cover crops through self‐seeding may increase adoption by reducing risk and cost. Winter rye (Secale cerealeL.), wheat (Triticum aestivumL.), and triticale (× TriticosecaleWittmack) were used to develop self‐seeding cover crop systems in a soybean [Glycine max(L.) Merr.]–corn (Zea maysL.) rotation. Cereal cover crops were planted in varying row spacing configurations and managed chemically and mechanically to achieve different levels of resource utilization in time and space. The objective of this study was to quantify interspecific competition of self‐seeded winter cereal cover crops growing concurrently with corn. Total weed density responded more to environment than cover crop treatment, with 12.0 and 2.2 weeds m−2in 2005 and 2006. Averaged across species, cover crop treatments lowered corn grain yield 5 to 22% compared with a no cover crop check. The most promising treatment lowered corn grain yield 7 and 11%, which is in the range for previously reported yield reduction using rye cover crops when rye was killed at or immediately after planting in a corn–soybean rotation. Cover crop regrowth intercepted <9% of photosynthetically active radiation (PAR) during early growth of corn. Combinations of lower corn plant population density and kernel density in cover crop treatments appear most responsible for the yield reduction. Additional research should focus on reducing interspecific competition during vegetative growth in corn when sink size is being determined.

Diversification of corn (Zea maysL.)–soybean [Glycine max(L.) Merr.] cropping systems can be achieved by incorporating winter cereal grains. Winter cereal grain production systems in the northern USA are inefficient in respect to annual radiation capture because the majority of these fields lay fallow until the following cropping season. The addition of a red clover (Trifolium pratenseL.) intercrop to winter cereal grains can supply forage and provide N to subsequent crops. The objective of this study was to determine the red clover dry matter (DM) and forage quality response to winter cereal species, cereal seeding rate, and red clover seeding rate. Winter wheat (Triticum aestivumL.) and triticale (×Triticosecalespp.) were seeded at 100, 200, 300, and 400 seed m−2in October 2002 and 2003. In March, red clover was frost‐seeded at 300, 600, 900, 1200, and 1500 seed m−2Red clover harvests in late summer, early fall, and the following spring yielded 6.2 to 8.5 Mg ha−1DM. Winter cereal species only affected red clover DM in the following spring of 1 yr. Cereal seeding rates impacted DM within specific harvest periods, but had no effect on seasonal totals or spring DM. Increasing red clover seeding rates increased final DM yield in four of six harvests. Increasing red clover seeding rate had no consistent effect on forage quality. Producers that intercrop red clover in winter wheat or triticale should frost‐seed at 900 to 1200 seed m−2to maximize DM yield.

Applying organic amendments to cropland affects corn (Zea maysL.) response to tillage systems differently. Identifying causes of the tillage by amendment interaction could match amendment inputs to responsive tillage systems. The objectives of this research were to determine if shoot dry matter (DM), nutrient uptake, and soil water use could explain the tillage by compost interaction for corn–grain yield. A corn–soybean [Glycine max(L.) Merr.]–wheat (Triticum aestivumL.)/clover (Trifoliumspp.) rotation, in all phases, with or without compost amendment, was initiated in 1998 in plots that had been managed with moldboard plow (MP), chisel plow (CT), or no‐tillage (NT) since 1988. Compost amendment increased corn whole‐plant P and K uptake 19 and 21%, averaged across 2 yr. No‐tillage increased whole‐plant P uptake 1 yr compared to MP and CT (113 vs. 65 kg ha−1) and increased grain P concentration (3.1 vs. 1.5 g kg−1). Compost provided no benefit (2 yr) or a negative effect (1 yr, 22%) to corn yield in MP. Compost provided no benefit to corn yield in CT. Corn growing in NT derived no benefit (2 yr) or a positive (1 yr, 9%) effect on grain yield from compost amendment. The tillage and compost responses observed in this study cannot be explained by plant N, soil water use, leaf gas exchange, or DM partitioning. Grain yield from soil managed using NT may respond to compost amendment, but reasons for this response remain unclear.

Soil protection and nutrient scavenging benefits of cover crops have been widely reported. Nevertheless, adoption of cover crops in agronomic farming systems is low. Cover crop systems that do not require annual planting may increase adoption. The objectives of this study were to compare self‐seeding and competitiveness of winter wheat (Triticum aestivumL.), triticale (x TriticosecaleWittmack), and rye (Secale cerealeL.) using different planting configurations and management options while growing concurrently with soybean [Glycine max(L.) Merr.]. Cover crops were planted with two or four 19‐cm rows between each 76‐cm soybean row. A no‐cover crop check treatment was also included for comparison. Cover crop species and species × management system interactions were not significant for seed production or soybean seed yield. Averaged across management system, cereals produced 10 656 and 4051 seeds m−2in 2004 and 2005. The two‐row band, no‐chop treatment (2RBNC) produced the most seed (20 347 and 14 511 seeds m−2) in 2004 and 2005, but also lowered soybean yield the greatest (45 and 40%). The four‐row treatment with a late glyphosate band (4RLB) was the least competitive and yielded 3114 and 3717 kg ha−1compared to 4019 and 4391 kg ha−1in the check. Wheat had the greatest self‐seeding, averaging about 31% of the original plant density. The four‐row treatment without a glyphosate band (4RNB) could be used in organic production systems, although additional research is needed to develop less competitive self‐seeding systems for conventional production systems.

Growing winter cereal grain/forage legume intercrops can provide multiple benefits to cropping systems in the North Central USA. Intercropping red clover (Trifolium pratenseL.) with winter cereal grains can provide forage and a green manure crop. Seeding rate recommendations for sole crops may not optimize intercrop system productivity if interactions exist. This study was conducted during the 2002–2003 and 2003–2004 growing seasons to determine optimum cereal grain and red clover forage seeding rates for maximum returns using partial budget analyses. In March, red clover was frost‐seeded at 0, 300, 600, 900, 1200, and 1500 seeds m−2into winter wheat (Triticum aestivumL.) and triticale (X TriticosecaleWittmack) seeded at 100, 200, 300, and 400 seeds m−2the previous October. Triticale and wheat maximized returns at seeding rates of 300 and 400 seeds m−2. No cereal grain by red clover seeding rate interactions were detected for red clover dry matter production (DM). Red clover plant densities after cereal grain harvest were 10 to 22% of the original seeding rates. Red clover DM production and return was maximized at 3.49 Mg ha−1with 900 seeds m−2in 2003 and 6.67 Mg ha−1with 1200 seeds m−2in 2004. Winter cereal/red clover intercrops in the North Central USA can maximize return using a cereal grain seeding rate between 300 and 400 seeds m−2and red clover seeding rates between 900 and 1200 seeds m−2

Frost‐seeding red clover (Trifolium pratenseL.) into winter cereals is a cost effective establishment method. Abiotic effects on seedling establishment have been reported, but information on cultivar differences is lacking. The objectives of this study were to quantify the effect of winter wheat (Triticum aestivumL.) on the establishment, persistence, and forage dry matter (DM) production of 15 red clover cultivars of diverse origin. Cultivars were frost‐seeded near Ames, IA in March of 2003 and 2004 and Prairie du Sac, WI in 2004. Presence of the wheat crop caused 19 and 23% mortality in 2003 and 2004 compared with the no‐wheat treatment in Iowa and 51% mortality in 2004 in Wisconsin. Dry matter yield of diploid cultivars exceeded tetraploids in all environments (439 vs. 559 g m−2). Favorable conditions for germination and emergence in 2003 resulted in high plant densities and no relationship between post‐wheat red clover density and DM yield. In 2004, unfavorable environmental conditions reduced plant densities, creating a relationship between red clover density (x) and DM yield (y) (y = 305 + 8.86x, R2= 0.65 in Iowa; y = 382 + 3.83x, R2= 0.22 in Wisconsin). The southern cultivar Cherokee generally had greater performance than the average northern cultivar. Differences across years and locations were inconsistent for elite and land races. Within different origins and selection histories, large variability exists in cultivar performance. More data are needed to determine if the cultivar‐by‐wheat interaction is important for screening cultivars for dual grain/forage systems.

Cover crops provide environmental and soil quality benefits, yet their adoption into production agriculture has been limited. This study was conducted to determine the influence of the growth stage and method of rye (Secale cerealeL.) control on soybean [Glycine max(L.) Merr.] development and resource utilization. Fall‐planted rye was controlled the following spring using a stalk chopper (mechanical) or glyphosate (chemical) at the second‐node, boot, and anthesis growth stages near Boone, IA, in 2002 and 2003. Regrowth from mechanical rye control in 2002 depleted soil water until rye matured. Maximum light interception by soybean was reduced by as much as 43 and 30% in chemical and 51 and 23% in mechanical control compared with the no‐rye check in 2002 and 2003. Dry matter (DM) accumulation was reduced by as much as 267 and 907 g m−2in chemical and mechanical control in 2002 compared with the check. In 2003, the range in DM accumulation was 242 g m−2. Rye delayed pod maturity in both years by as much as 7.9 d. Producers who adopt these methods of rye management can expect delayed soybean maturity and reduced DM accumulation.

Cover crops provide many environmental and soil quality benefits, yet their adoption into production agriculture has been limited by insufficient management information. This study was conducted to determine a combination of method and timing of rye (Secale cerealeL.) control that would not hinder soybean [Glycine max(L.) Merr.] growth or result in resource competition. The effects of mechanical and chemical rye control at 2nd node, boot, and anthesis growth stages on soil water, light interception, soybean growth and maturity were investigated near Boone, IA, on Spillville loam (Fine-loamy, mixed, superactive, mesic Cumulic Hapludolls), and Clarion loam (Fine-loamy, mixed, superactive, mesic Typic Hapludolls) in 2002 and 2003 growing seasons. In 2002, untimely rainfall reduced soil water 0.0325 kg kg-1from 2nd node to anthesis in the 0–15 cm depth in chemical control. In mechanical control, rye depleted soil water until it matured, at which point larger plants in check subplots utilized soil water at a higher rate than soybean in treatments with rye. Soybean light interception was reduced by rye in mechanical treatments in both years. Anthesis and check plots in chemical control had similar values for light interception. Biomass accumulation was lower under mechanical control than chemical control. However, even the best treatment in chemical control, anthesis, accumulated 140 g m–2less biomass than check treatments in 2002. All treatments containing rye delayed maturity. Anthesis timing matured closest to check subplots at 6.5 and 3.8 days after the check in 2002 and 2003, respectively. The possibility of allelopathy delaying maturity is worthy of further investigation. Chemical control at anthesis was the most effective management system next to the check, differing significantly only in date of maturity. Periods of low rainfall, ineffective rye control, and possible allelopathy were critical limiting factors in this rye cover crop system.

Regression analysis of repeated‐measures data from plots in large experiments is both labor intensive and time consuming. When duration estimates characterizing each individual repeated‐measures series are of interest, numerical integrations are possible alternatives. This note evaluates a trapezoidal rule for estimating a wetness duration index that is derived from repeated tensiometer readings of matric potential associated with plots in a recent soybean [Glycine max(L.) Merr.] study. Tensiometer repeated‐measures series were randomly selected from four of the treatments with their replications for a total of 15 plots (of 420 total) associated with a 2‐yr experiment. Regression‐based duration estimates were developed and compared with those derived using an unequally spaced trapezoidal rule. Equivalence between the two estimators was assessed based on multiple statistical analyses. The estimators were virtually identical by all criteria. The numerical method is faster and easier to employ. Furthermore, the concept can be applied to other repeated measurements, and the results may be useful as covariates in other analyses.

Soybean [Glycine max(L.) Merr.] producers in many regions of the USA are confronted with significant yield losses because of crop damage from white‐tailed deer (Odocoileus virginianus). Our objectives were to quantify soybean resource utilization and yield responses to variety, row spacing, and simulated repeated biomass removal. Field research was conducted in 2000 and 2001 on a Quakertown silt loam soil (fine‐loamy, mixed, mesic Typic Hapludult) near Pittstown, NJ. Biomass removal during early vegetative and vegetative/reproductive growth extended the soil wetness duration index on average by 1.5 and 2.9 d compared with the control from the 0‐ to 30‐ and 30‐ to 60‐cm soil depths in 2000 and by 5.1 and 2.1 d in 2001. Biomass removal during early vegetative growth delayed pod maturity up to 7 d compared with the control, but biomass removal during reproductive growth hastened pod maturity by as much as 3 d. Averaged across row spacing and biomass removal, variety ‘APK394NRR’ yielded 12 and 24% lower than ‘93B53’ in 2000 and 2001. In 2000, averaged across variety and biomass removal, the 20‐ and 41‐cm row widths yielded 19 and 16% less than the 76‐cm row width. Averaged across variety and row spacing, all biomass removal treatments lowered yield compared with the control except the midvegetative/early reproductive treatment in 2001 (661 vs. 663 g m−2). The greatest yield reductions occurred (up to 89%) when biomass was removed repeatedly during vegetative and reproductive growth. Management implications for soybean producers include variety selection and row spacing to diminish the effects of deer damage.

Determining the extent of change in fresh versus field‐cured grass hay quality, mineral, and NO3‐N concentrations under rain‐free conditions provides valuable information to hay producers. The objectives of this research were to evaluate the effect of fresh vs. field‐cured forage on crude protein (CP), neutral detergent fiber (NDF), total digestible nutrients (TDN), P, K, Ca, and NO−3‐N concentrations of orchardgrass (Dactylis glomerataL.), smooth bromegrass (Bromus inermisLeyss.), and timothy (Phleum pratenseL.), and to determine if interactions with N rate exist. At the low N rate in 1999 and 2000, orchardgrass CP in fresh and field‐cured forage, NDF, and TDN concentrations were different. Orchardgrass P and K concentrations were lower in field‐cured compared with fresh forage, but differences were inconsistent across N rates. In contrast, smooth bromegrass K (23 vs. 27 g kg−1) and Ca (4.3 vs. 6.2 g kg−1) concentrations were greater in field‐cured compared with fresh forage in 1999 across N rates. Tissue NO−3‐N concentration was greater in field‐cured orchardgrass at all N rates and at the low N rate in smooth bromegrass in 1999. Interactions between N rate and fresh vs. field‐cured smooth bromegrass were detected for all variables in 1999 and orchardgrass K concentration in 2000. These results demonstrate that changes in grass quality, mineral, and tissue NO−3‐N concentrations occur under rain‐free field curing conditions. Consequently, forage scientists conducting research on grass hay quality indices and mineral content should sample subsequent to field‐curing to provide accurate results.

Numerous studies have evaluated growth, stand dynamics, and botanical composition of grass swards separately, but little information is available on the interaction of these factors. The objectives of this study were to determine the response of growth rate, tiller density, and botanical composition in orchardgrass (Dactylis glomerataL.), smooth bromegrass (Bromus inermisLeyss.), and timothy (Phleum pratenseL.) to different N levels. Growth rates ranged from 8.6 to 1.54, 9.14 to 0.67, and 4.19 to 0.29 g dry matter (DM) m−2d−1in orchardgrass, smooth bromegrass, and timothy. Orchardgrass growth rates responded to changes in abiotic conditions, while smooth bromegrass and timothy expressed less plasticity under favorable growth environments. All species exhibited temporal fluctuations in tiller density. Orchardgrass and smooth bromegrass tiller densities were not closely associated with yield, presumably because of compensation in tiller weight. Nitrogen did not affect tiller density during the first production year, but orchardgrass tiller density was influenced by N throughout the second production year, including the fall growth period, when tiller density in all species was affected. Aggressive growth rates in orchardgrass reduced species diversity by 65% by the end of the second production year. Total diversity in smooth bromegrass decreased from 7.2 to 3.5 species 0.25 m−2compared with an increase in timothy from 1.5 to 5.7 species 0.25 m−2due to a combination of slow growth and reduced tiller density. Orchardgrass and smooth bromegrass are superior to timothy in Northeast hay production systems because of greater DM production and less weed competition.

Biomass removal effects on soybean [Glycine max(L.) Merr.] light interception and yield under different row spacings have not been documented. Objectives for this study were to evaluate biomass removal, light interception, seed yield, and yield components of soybean under seven clipping treatments. Treatments in this study were clipping at V5, R1, R4, V5 + R1, V5 + R4, R1 + R4, and V5 + R1 + R4, and a control in 18‐ or 20‐cm and 76‐cm rows. In 1998, a dry year, biomass removal exhibited a negative linear relationship with seed yield in narrow rows (r2= 0.62). A row spacing–clipping interaction was observed. In wide rows, clipping at V5 or R1 produced a compensatory response by increasing yield 12 and 5%, respectively. Generally, soybean in 76‐cm rows maintained seed yield by adjusting the number of pods or seed weight, except when clipping occurred at V5 + R4 or at three growth stages. In 1999, under severe moisture stress, row spacing influenced seed yield. Averaged across clipping treatments, narrow rows yielded 16% more (301 vs. 254 g m−2) than wide rows. Generally, soybean yield declined as clipping timing was delayed and as clipping frequency increased in narrow rows, except when clipping occurred at V5 + R1. Clipping at V5 and V5 + R1 did not affect yield in wide rows. All other clipping treatments suffered yield reductions ranging from 20 to 58%. A quadratic relationship (R2= 0.83) was observed between biomass removal and seed yield.

The USDA has a goal of implementing integrated pest management (IPM) practices on 75% of the cropland in the USA so growers may adopt weed control practices that emphasize crop rotation and cultivation. Our objectives were to estimate weed densities in corn (Zea maysL.) and to examine weed emergence in an unmanaged weed area of corn following 4 yr of continuous corn, which received preemergence broadcast herbicides, and following soybean [Glycine max(L.) Merr.]–corn and soybean–wheat (Triticum aestivumL.)/red clover (Trifolium pratenseL.)–corn cropping systems, which received banded herbicides and cultivation, on four farms in New York. More total weeds emerged at two sites and more perennial weeds emerged at all sites in the unmanaged weed area of corn in the soybean–wheat/red clover–corn cropping system compared with continuous corn because of poor red clover establishment, which resulted in a fallow period after wheat harvest. Weed densities in corn averaged 6.3 and 9.9 weeds m−2in the soybean–wheat/red clover–corn cropping system, compared with 1.7 and 1.0 weeds m−2in continuous corn at two of the sites, because of greater weed emergence and unsatisfactory weed control with banded herbicides and a single cultivation in the soybean–wheat/red clover–corn cropping system. When red clover does not establish well, growers should expect increased weed densities in the subsequent corn crop. Growers should then consider fall tillage or herbicide application after wheat harvest, or additional cultivation(s) or herbicide applications in the subsequent corn crop.

Rotation effects on corn (Zea maysL.) growth have not been documented. Our objective was to evaluate dry matter (DM) and N accumulation of corn following corn, soybean [Glycine max(L.)Merr.], or wheat/red clover (Triticum aestivumL./Trifolium pratenseL.) using moldboard plow, chisel, and ridge tillage under high (broadcast herbicides and 163 kg N ha−1) and low chemical management (banded herbicides and 95 kg N ha−1). In 1993, corn following soybean, compared with corn under high chemical management, had greater DM and N accumulation during vegetative development but similar N accumulation after silking (45 kg ha−1) and yield (7.6 and 7.2 Mg ha−1, respectively). In 1994, corn following soybean, compared with corn under high chemical management, had similar DM and N accumulation during vegetative development, but greater N accumulation (59 and 35 kg ha−1, respectively) after silking and yield (11.4 and 10.7 Mg ha−1). Corn following wheat/clover under both management systems, compared with corn following corn under high chemical management, had greater DM and N accumulation during vegetative development in 1994. Corn following wheat/clover under high chemical management had the greatest N accumulation after silking (79 kg ha−1) and yield (12.0 Mg ha−1), whereas the other two systems had the same N accumulation after silking and yield. Corn yield had linear responses to N accumulation after silking in 1993 (r2= 0.47) and 1994 (r2= 0.87). We conclude that N accumulation after silking influenced the yield response to rotation more than DM and N accumulation during vegetative development did.

Surveying end‐users about their use of technologies and preferences provides information for researchers and educators to develop relevant research and educational programs. A mail survey was sent to Corn Belt farmers during 2006 to quantify cover crop management and preferences. Results indicated that the dominant cereal cover crops in Indiana and Illinois are winter wheat (Triticum aestivumL.) and cereal rye (Secale cerealeL.), cereal rye and oat (Avena sativaL.) in Iowa, and oat in Minnesota. Legumes were used more frequently in Indiana and Illinois, and red clover (Trifolium pratenseL.) was the dominant choice across the region. Farmers relied solely on herbicides 54% of the time to kill cover crops. Ninety‐three percent of respondents indicated that they received no cost sharing for using cover crops and 14% indicated that they would plant cover crops on rented land. Corn Belt farmers prefer cover crops that overwinter (68%) and fix N (64%). The information provided in this survey supplements existing knowledge that can be used to develop relevant research and educational programs to address agronomic production systems that include cover crops.

Despite evidence for biological control in North America, outbreaks of the invasive soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae), continue to occur on soybean (Glycine max L. Merr.). Our objectives were to determine whether natural enemies delay aphid establishment and limit subsequent population growth and whether biological control can be improved by altering the within-field habitat. We hypothesized that a living mulch would increase the abundance of the aphidophagous community in soybean and suppress A. glycines establishment and population growth. We measured natural enemy and A. glycines abundance in soybean grown with and without an alfalfa (Medicago sativa L.) living mulch. Soybean grown with an alfalfa living mulch had 45% more natural enemies and experienced a delay in A. glycines establishment that resulted in lower peak populations. From our experiments, we concluded that the current natural enemy community in Iowa can delay A. glycines establishment, and an increase in aphidophagous predator abundance lowered the rate of A. glycines population growth preventing economic populations (i.e., below the current economic threshold) from occurring. Incorporation of a living mulch had an unexpected impact on A. glycines population growth, lowering the aphids’ intrinsic rate of growth, thus providing a bottom-up suppression of A. glycines. We suggest future studies of living mulches or cover crops for A. glycines management should address both potential sources of suppression. Furthermore, our experience suggests that more consistent biological control of A. glycines may be possible with even partial resistance that slows but does not prevent reproduction.