John A. Lamb

Soil strength and water content influences on corn root distribution in a sandy soil

Initial field observations revealed a shallow corn (Zea mays L.) root system on a Zimmerman fine sand in a corn/soybean (Glycine max L.) rotation. Since root distribution influences crop water and nutrient absorption, it is essential to identify factors limiting root growth. The objective of this study was to determine the factor(s) limiting corn rooting depth on an irrigated fine sand soil. Bulk density, saturated hydraulic conductivity, and soil water retention were measured on undisturbed soil cores. Corn root distribution assessed at tasseling over a 3-yr period showed an average of 94% of total root length within the upper 0.60 m of soil with 85% in the upper 0.30 m of soil. Mechanical impedance was estimated with a cone penetrometer on two dates with differing water contents. Cone penetrometer measurements greater than 3 MPa indicated mechanical impedance in soil layers extending from 0.15 to 0.35 m deep. Penetration resistance decreased as soil water content increased. However, soil water contents greater than field capacity were required to decrease penetration resistance below the 3 MPa threshold. Such water saturated conditions only occurred for short periods immediately after precipitation or irrigation events, thus roots usually encountered restrictive soil strengths. The soil layer from 0.15 to 0.60 m had high bulk density, 1.57 Mg m-3. This compacted soil layer, with slower saturated hydraulic conductivities (121 to 138 mm hr-1), held more water than the soil above or below it and reduced water movement through the soil profile. Crop water use occurred to a depth of approximately 0.75 m. In conclusion, a compacted soil layer confined roots almost entirely to the top 0.60 m of soil because it had high soil strength and bulk density. The compacted layer, in turn, retained more water for crop use.

Impact of manure application on soil phosphorus sorption characteristics and subsequent water quality implications

For nutrient management purposes, it is important to understand the impact of manure application on soil phosphorus (P) sorption characteristics and what it means with regard to potential environmental problems. The objectives of this study were (i) to determine whether previous manure applications impact P sorption capacity and strength; (ii) to characterize the relationship between water soluble-P (WSP) and degree of P saturation (DPS); and (iii) to characterize the relationship between WSP and P sorption capacity and strength. Phosphorus sorption isotherms were constructed for seven pairs of soils with and without a history of manure application. Within a soil series, P sorption isotherms were compared to determine the effects of manure application. Manure application increased sorption capacity significantly in the Nicollet soil series. Phosphorus sorption capacity was unchanged by manure application in the Waukegan soil series. Manure application reduced P sorption capacity in the Port Byron, Sanburn, Verndale, Ves, and Barnes soils. Phosphorus sorption strength decreased in five of the seven soil series after manure application. The degree of P saturation and soil test P were strongly linearly correlated to WSP. Water soluble-P was less than 1 mg L−1 when DPS was less than 21.7%. When manure application increased DPS to more than 26%, sorption strength was reduced; P was bound less tightly to the soil on low strength sorption sites, such that P was more readily available. Sorption strength was used to determine the soil test P level above which there is increased risk to water quality because of reduced sorption strength and subsequent increases in WSP; this occurred when Bray-P was greater than 60 mg kg−1. Phosphorus sorption strength seems to be the sorption property that is most sensitive to applications of P.

The Impact of Corn Stover Removal on N2O Emission and Soil Respiration: an Investigation with Automated Chambers

Corn stover removal, whether for silage, bedding, or bioenergy production, could have a variety of environmental consequences through its effect on soil processes, particularly N2O production and soil respiration. Because these effects may be episodic in nature, weekly snapshots with static chambers may not provide a complete picture. We adapted commercially available automated soil respiration chambers by incorporating a portable N2O analyzer, allowing us to measure both CO2 and N2O fluxes on an hourly basis through two growing seasons in a corn field in southern Minnesota, from spring 2010 to spring 2012. This site was part of a USDA multilocation research project for five growing seasons, 2008–2012, with three levels of stover removal: zero, full, and intermediate. Initially in spring 2010, two chambers were placed in each of the treatments, but following planting in 2011, the configuration was changed, with four chambers installed on zero removal plots and four on full removal plots. The cumulative data revealed no significant difference in N2O emission as a function of stover removal. CO2 loss from the full removal plots was slightly lower than that from the zero removal plots, but the difference between treatments was much smaller than the amount of C removed in the residue, implying loss of soil carbon from the full removal plots. This is consistent with soil sampling data, which showed that in five of six sampled blocks, the SOC change in the full removal treatments was negative relative to the zero removal plots. We conclude that (a) full stover removal may have little impact on N2O production, and (b) while it will reduce soil CO2 production, the reduction will not be commensurate with the decrease in fresh carbon inputs and, thus, will result in SOC loss.

Effect of manure on accumulation of dry matter, nitrogen, and phosphorus by soybean

Manure application for soybean [Glycine max (L.) Merr.] production is being considered by livestock producers, but the manures influence on dry matter (DM), nitrogen (N), and phosphorus (P) accumulation is not well documented. The objectives of this study were to measure N, P, and DM accumulation patterns and quantities by three genetically-different soybean varieties. Two preplant, sweep-injected manure application rates and a control were main plot treatments and three soybean varieties were subplots at seven experimental sites in 1996 and 1997. Starting in mid-June and continuing on a 15-d schedule until maturity, whole-plant samples were collected, dried, weighed, and analyzed for N and P. Plant DM increased with increasing manure rates at each sampling after mid-June. Nitrogen concentration differences among manure rates were greatest early in the season and diminished with time, whereas P concentration differences were consistent throughout the sampling period. Compared to the control treatment, manure resulted in an average of 25% more N accumulation at the first sampling date, 35% more at the second sampling, 42% at the third sampling, and then steadily decreased to a 10% increase at the final sampling date. Similar to N accumulation, mean P accumulation differences between the control and the manure treatments increased to 27% at the third sampling and then gradually decreased to 14% by the final sampling date. The overall effect of variety was minimal, yet statistically significant, and interactions between manure rate and variety were not found. Applying manure for soybean increased end-of-season accumulation of DM, N, and P by 9, 10, and 14%, respectively, compared to the non-manure treatment.

REDIRECTION OF PRECIPITATION BY A CORN CANOPY AND RELATED SOILWATER STATUS

Redirection of precipitation by a crop canopy significantly affects the distribution of water entering soil. This knowledge can be used to improve crop management practices for protecting ground water. Over a 4-y period, rain and/or irrigation water was collected at 8 equidistant positions between corn (Zea mays L.) rows. Soil water status was measured to a 0.3-m depth in the same relative positions. Wind direction and speed, and crop canopy development influenced the location where throughfall entered the soil surface and resultant soil water content. Stemflow increased to > 60% of incoming precipitation with canopy closure in most years. These large amounts of water entering the soil as stemflow increased percolation in the row and soil water content below the row, the zone of greatest depletion of plant available water. Associated with canopy closure, reduced throughfall reached the soil surface within 0.2 m of the row; hence, a reduced potential for leaching of agrichemicals applied in this area. * Minnesota Agric. Exp. Stn. Scientific J. Series No. 991250097.

Evaluation of methods to determine residual soil nitrate zones across the northern Great Plains of the USA

A four-year study was conducted from 2000 to 2004 at eight field sites in Montana, North Dakota and western Minnesota. Five of these sites were in North Dakota, two were in Montana and one was in Minnesota. The sites were diverse in their cropping systems. The objectives of the study were to (1) evaluate data from aerial photographs, satellite images, topographic maps, soil electrical conductivity (ECa) sensors and several years of yield to delineate field zones to represent residual soil nitrate and (2) determine whether the use of data from several such sources or from a single source is better to delineate nitrogen management zones by a weighted method of classification. Despite differences in climate and cropping, there were similarities in the effectiveness of delineation tools for developing meaningful residual soil nitrate zones. Topographic information was usually weighted the most because it produced zones that were more correlated to actual soil residual nitrate than any other source of data at all locations. The soil ECa sensor created better correlated zones at Minot, Williston and Oakes than at most eastern sites. Yield data for an individual year were sometimes useful, but a yield frequency map that combined several years of standardized yield data was more useful. Satellite imagery was better than aerial photographs at most locations. Topography, satellite imagery, yield frequency maps and soil ECa are useful data for delineating nutrient management zones across the region. Use of two or more sources of data resulted in zones with a stronger correlation with soil nitrate.

Influence of rate and placement of phosphate fertilizer on growth and yield of hard red spring wheat in diverse tillage systems

Management of P is a major issue for crop producers who grow hard red spring wheat (Triticum aestrivum, L.) with conservation tillage. Compared to the use of the moldboard plow, tillage that leaves crop residue on the soil surface can cause changes in soil chemical, biological, and physical properties. These changes may affect management practices for fertilizer P. Two studies were conducted to evaluate the impact of rate and placement of fertilizer P on hard red spring wheat production in various tillage systems. In one study, P rates of 0, 5.5, 11.0, 16.5, and 22.0 kg ha−1 were: (1) broadcast and incorporated, or (2) applied in a subsurface band prior to tillage, or placed with the seed at planting. The chisel plow was used for primary tillage in this study. In a separate study, P rates of 0, 20, 40, and 60 kg ha−1 were: (1) broadcast and incorporated, (2) applied in a subsurface band, or (3) applied with the seed at planting. These P rates and placements were used in a moldboard plow, chisel plow, and no-till planting system. There was a positive response to rate of fertilizer P used in both studies, with a higher rate needed for optimum yield when soil test levels for P were in the low rather than the medium range. Tillage system had an effect on yield with no-till < chisel plow < moldboard plow. There was no interaction between: (1) tillage system and rate of P applied, (2) tillage system and P placement, and (3) rate and placement of P fertilizer. The data collected from these studies lead to the conclusion that the recommended rate of fertilizer P should not be adjusted for either method of placement or tillage system.

Maize Stover and Cob Cell Wall Composition and Ethanol Potential as Affected by Nitrogen Fertilization

Maize (Zea mays L.) stover and cobs are potential feedstock sources for cellulosic ethanol production. Nitrogen (N) fertilization is an important management decision that influences cellulosic biomass and grain production, but its effect on cell wall composition and subsequent cellulosic ethanol production is not known. The objectives of this study were to quantify the responses of maize stover (leaves, stalks, husks, and tassel) and cob cell wall composition and theoretical ethanol yield potential to N fertilization across a range of sites. Field experiments were conducted at rainfed and irrigated sites in Minnesota, USA, over a 2-year period. Stover cell wall polysaccharides, pentose sugar concentration, and theoretical ethanol yield decreased as N fertilization increased. Stover Klason lignin increased with N fertilization at all sites. Cob cell wall composition was less sensitive to N fertilization, as only pentose and Klason lignin decreased with N fertilization at two and one site(s), respectively, and hexose increased with N fertilization at one of eight sites. Cob theoretical ethanol yield was not affected by N fertilization at any site. These results indicate variation in stover cellulosic ethanol production is possible as a result of N management. This study also demonstrated that cell wall composition and subsequent theoretical ethanol yield of maize cobs are generally more stable than those with stover because of overall less sensitivity to N management.

MODELING OF SUGARBEET QUALITY VARIABLES FROM CANOPY SPECTRAL INDICES IN A FERTILITY TRIAL

Sugarbeet quality varies inversely with N fertility, while gross yield varies positively with N. Existing models of yield from remotely sensed data do not consider crop quality. A fertility trial was used as the basis for a canopy reflectance study to correlate quality variables to canopy characteristics. Sugarbeet canopy reflectance and radiance were measured with a portable spectroradiometer, and from airborne images of the trial plots. Canopy data were collected five times from early August to early October of 1999. Linear regression models were used to correlate canopy indices to sugarbeet quality variables on each date. Both a green NDVI and the conventional NDVI indices showed strong correlation to recoverable sucrose concentration in sugarbeet roots. Correlations to harvest quality in October were highest in spectral measurements taken in early to mid–August. Other quality variables including root concentrations of sodium, potassium, and amino–N were poorly correlated to spectral properties of the canopy. The results suggest that a single image of a field in August could provide spatial indication of variability in root quality.

Rotating alfalfa with dry bean as an alternative to corn-soybean rotations in organic systems in the Upper Midwest

Dry bean (Phaseolus vulgaris) can be grown as a local food source and as an alternative to soybean (Glycine max) to diversify organic crop rotations. To understand the benefits of diversification of organic cropping systems, the effects of preceding alfalfa (Medicago sativa) and corn (Zea mays) crops on yields of five dry bean types and one soybean type, and the effect of bean type on following spring wheat (Triticum aestivum) yields, were tested at four Minnesota locations. Dry bean and soybean yields following alfalfa were 25% greater than yields following corn at two of four locations, though bean yields following corn were greater at one location. A preceding alfalfa crop benefited bean yields at locations where hog manure or no manure was applied to corn, whereas bean yields following corn fertilized with cow manure were similar to or greater than bean yields following alfalfa. Among dry bean types, black bean yielded similarly to soybean at three of four locations, but dark red kidney bean consistently yielded 25–65% lower than soybean. Navy, pinto and heirloom dry bean types yielded similarly to soybean at two of four locations. Across locations, weed biomass was 3–15 times greater in dry bean than in soybean and dry bean yield response to weed competition varied among bean types. However, dry bean, regardless of the preceding crop, demonstrated the potential to produce yields comparable with soybean in organic systems and the substitution of dry bean for soybean did not affect subsequent wheat yields. More studies are needed to identify nitrogen fertility dynamics in organic systems as they relate to dry bean yield.