No-till Maize Research Articles

Soil Carbon Sequestration by Switchgrass and No-Till Maize Grown for Bioenergy

Net benefits of bioenergy crops, including maize and perennial grasses such as switchgrass, are a function of several factors including the soil organic carbon (SOC) sequestered by these crops. Life cycle assessments (LCA) for bioenergy crops have been conducted using models in which SOC information is usually from the top 30 to 40 cm. Information on the effects of crop management practices on SOC has been limited so LCA models have largely not included any management practice effects. In the first 9 years of a long-term C sequestration study in eastern Nebraska, USA, switchgrass and maize with best management practices had average annual increases in SOC per hectare that exceed 2 Mg C year−1 (7.3 Mg CO2 year−1) for the 0 to 150 soil depth. For both switchgrass and maize, over 50 % of the increase in SOC was below the 30 cm depth. SOC sequestration by switchgrass was twofold to fourfold greater than that used in models to date which also assumed no SOC sequestration by maize. The results indicate that N fertilizer rates and harvest management regimes can affect the magnitude of SOC sequestration. The use of uniform soil C effects for bioenergy crops from sampling depths of 30 to 40 cm across agro-ecoregions for large scale LCA is questionable.

Influence of tillage on maize yield in soil with shallow fragipan

A genuine concern for landowners and other stake holders is whether conservation tillage contaminates shallow groundwater even though it greatly reduces erosion. A six-year continuous maize (Zea mays L.) study that compared yields from no-tillage (NT), reduced-tillage (RT), and conventional-tillage (CT) was conducted in the upland hills of northern Mississippi on 4–6% sloping soils overlying a shallow fragipan. The objective was to test the hypothesis that neither no-tillage nor reduced-tillage has the same effect on maize crop as conventional-tillage on soils with a shallow water restricted layer. The study showed conservation tillage had fewer detrimental effects on the water quality in runoff and shallow groundwater and promoted more soil water for crop use during the growing season than conventional tillage. With adequate weed control, NT produced higher yields than CT on these silt loam soils due to soil water conservation. However, inadequate weed control occurred in several years of the study along with above normal rain resulting in lower NT maize yields than CT yields. Significant differences in maize yield were found for type of tillage, year, and tillage-year interaction. These differences were explained by a tillage system's ability to conserve soil water and control weeds. Other results included low sediment amounts lost from NT maize plots and insignificant free water quantities at the fragipan's surface during the cropping season for all tillage systems. Maximum groundwater movement across the surface of the fragipan occurred during the non-cropping season under soil profile saturation. Amount, timing, and distribution of rainfall rather than tillage system primarily influenced agrichemical movement from maize systems in this study. Some form of conservation tillage that decreases or prevents erosion will be required on sloping lands with shallow fragipan to sustain long term continuous corn production. Information from this study provides additional guidance for making tillage and pesticide management recommendations to farmers.

The Effects of a Winter Cover Crop on Diabrotica virgifera (Coleoptera: Chrysomelidae) Populations and Beneficial Arthropod Communities in No-Till Maize

The effects of an autumn-planted, spring-killed, grass cover crop (Elymus trachycaulus [Link] Gould ex Shinners) on populations of Diabrotica virgifera virgifera LeConte and its predator community were evaluated in South Dakota maize fields over two seasons. Abundance and size of D. virgifera larvae and adults and sex ratio of adults were measured in maize produced under two treatments (i.e., a winter cover crop or bare soil), as were maize root damage and the abundance and diversity of the predator communities collected on the soil surface and in the soil column. First and second instars and adults of D. virgifera were similarly abundant in the two treatments, but third instars were significantly fewer in maize planted after a winter cover crop. Larvae developed at different rates in the two treatments, and second instars were significantly smaller (head capsule width and body length) in the maize planted after a cover crop. First and third instars and adults were of similar size in the two treatments, and adult sex ratios were also similar. Although initially similar, predator populations increased steadily in the cover-cropped maize, which led to a significantly greater predator population by the time D. virgifera pupated. There was significantly less root damage in the cover-cropped maize. Predator communities were similarly diverse in both treatments. Predator abundance per plot was significantly and negatively correlated with the abundance of third instars per plot. Clearly, winter cover crops reduce D. virgifera performance and their damage to the crop, and we suspect that this reduction is caused by both environmental effects of the treatment on D. virgifera size and development, and of increased predation on the third instars of the pest. Additional data on the impact of cover crops on actual predation levels, grain yield and quality, and farmer profitability, and correlations among pest performance, crop characteristics, and predator populations and behaviors are key components of this system that remain to be addressed.

Soil nitrous oxide emissions in long-term cover crops-based rotations under subtropical climate

It has been shown that cover crops can enhance soil nitrous oxide (N 2O) emissions, but the magnitude of increase depends on the quantity and quality of the crop residues. Therefore, this study aimed to evaluate the effect of long-term (19 and 21 years) no-till maize crop rotations including grass [black oat ( Avena strigosa Schreb)] and legume cover crops [vetch ( Vigna sativa L.), cowpea ( Vigna unguiculata L. Walp), pigeon pea ( Cajanus cajan L. Millsp.) and lablab ( Dolichos lablab)] on annual soil N 2O emissions in a subtropical Acrisol in Southern Brazil. Greater soil N 2O emissions were observed in the first 45 days after the cover crop residue management in all crop rotations, varying from −20.2 ± 1.9 to 163.9 ± 24.3 μg N m −2 h −1. Legume-based crop rotations had the largest cumulative emissions in this period, which were directly related to the quantity of N ( r 2 = 0.60, p = 0.13) and inversely related to the lignin:N ratio ( r 2 = 0.89, p = 0.01) of the cover crop residues. After this period, the mean fluxes were smaller and were closely related to the total soil N stocks ( r 2 = 0.96, p = 0.002). The annual soil N 2O emission represented 0.39–0.75% of the total N added by the legume cover crops. Management-controlled soil variables such as mineral N (NO 3 − and NH 4 +) and dissolved organic C influenced more the N 2O fluxes than environmental-related variables as water-filled pore space and air and soil temperature. Consequently, the synchronization between N mineralization and N uptake by plants seems to be the main challenge to reduce N 2O emissions while maintaining the environmental and agronomic services provided by legume cover crops in agricultural systems.

Monoculture Maize (Zea mays L.) Cropped Under Conventional Tillage, No-tillage and N Fertilization: (II) Fumonisin Incidence on Kernels

Planting maize under no-tillage is an increasing farming practice for sustainable agriculture and sound environmental management. Although several studies on yield of no-till maize have been done, there is few information about the effect of tillage on fumonisin contamination. The present study was done to determine the effect of notillage and conventional tillage with two rates of nitrogen on fumonisin content in kernels of continuous maize. Average grain contamination with fumonisins B1 and B2 over the years 2004-06 was not significantly different, with mean values of 1682, 1984 and 2504 μg kg-1, respectively. Fumonisin B1 was the most abundant toxin found in the samples. No-tillage significantly affected the incidence of fumonisins during the first year of the trial, in which fumonisin content was significantly higher with no-till (2008 μg kg-1) compared with conventional tillage (1355 μg kg-1). However, no-tillage did not significantly affect the incidence of fumonisins in the second and third years of the study. Fumonisin content at the rate of 300 kg N ha-1 was not statistically different compared to that obtained without N fertilization. The interaction between the soil management system and the rate of applied nitrogen was only evident in the second year. Our results indicate that fumonisin contamination was affected by no-tillage only in the first year. Nitrogen fertilization had no significant effect on fumonisin content in any year. The weather conditions during susceptible stages of maize development have probably overridden the effect of nitrogen fertilization.

Assessment of the mycorrhizal community in the rhizosphere of maize ( Zea mays L.) genotypes contrasting for phosphorus efficiency in the acid savannas of Brazil using denaturing gradient gel electrophoresis (DGGE)

Community structure of indigenous arbuscular mycorrhizal fungi (AMF) in the rhizosphere of tropical maize genotypes contrasting for phosphorus efficiency was evaluated using denaturing gradient gel electrophoresis (DGGE). Fragments of AMF ribosomal DNA (rDNA) were amplified using nested PCR with fungal universal primers and ITS (internal transcribed spacer) specific primers for Acaulosporaceae, Glomaceae and Gigasporaceae. ITS-Acaulosporaceae and Glomaceae-specific primers and DGGE were efficient in differentiating the composition of mycorrhizal communities. Maize genotypes had a greater influence on the rhizosphere mycorrhizal community than the level of P in the soil. DGGE profiles of maize roots revealed bands that were present only in P efficient genotypes (L3 and HT3060), suggesting that some mycorrhizal groups were stimulated by P efficient maize genotypes. Acaulospora longula, A. rugosa, A. scrobiculata, A. morrowiae and Glomus caledonium were found only in the rhizosphere of P efficient maize genotypes cultivated in low P soils. A greater number of mycorrhizal DGGE bands were found in soil samples from no-till maize than conventional tillage. Effective mycorrhizal colonization of crops may influence the maize yield under Brazilian savanna acid soils by modulating the capacity of different cultivars to tolerate P deficiency.

Efeito de doses e da época de aplicação de nitrogênio nos caracteres agronômicos da cultura do milho sob plantio direto

A cultura do milho é de grande importância na região Centro-Oeste para produção de grãos. Com o objetivo de avaliar o efeito da melhor dose e época de aplicação de N nos caracteres agronômicos do milho em sistema plantio direto, instalou-se um ensaio no município de Rio Verde (GO), no ano agrícola 2002/03. O delineamento experimental empregado foi o de blocos casualizados, em esquema fatorial 6 x 4 + 1, com quatro repetições, sendo constituído por seis épocas de aplicação de N (antecipada; semeadura; 30 dias em cobertura; semeadura mais 30 dias em cobertura; semeadura mais 30 e 45 dias em cobertura; e antecipada mais semeadura mais 30 dias em cobertura) e quatro doses de N (25, 50, 100 e 150 kg ha-1), acrescido da testemunha sem a aplicação de N. Foi utilizado o híbrido P30K75 e a uréia como fertilizante nitrogenado. A dose de 150 kg ha-1 proporcionou maiores valores de rendimento de grãos, teor de N nas folhas, peso de grãos por espiga e altura de plantas. Os maiores teores de N nas folhas foram obtidos nas aplicações em cobertura, semeadura mais 30 dias em cobertura e semeadura mais 30 e 45 dias em cobertura. As aplicações de N em cobertura (30 dias) e parcelada (antecipada mais semeadura mais 30 dias em cobertura) proporcionaram maiores pesos de grãos por espiga e de mil grãos. Não foi constatado efeito significativo das doses e épocas de aplicação de N para rendimento de proteína e severidade de doenças. A maior rentabilidade da aplicação de N foi obtida com aplicação de 25 kg ha-1 na semeadura.

Potential of Carbon Accumulation in No‐Till Soils with Intensive Use and Cover Crops in Southern Brazil

The area under no-till (NT) in Brazil reached 22 million ha in 2004-2005, of which approximately 45% was located in the southern states. From the 1970s to the mid-1980s, this region was a source of carbon dioxide to the atmosphere due to decrease of soil carbon (C) stocks and high consumption of fuel by intensive tillage. Since then, NT has partially restored the soil C lost and reduced the consumption of fossil fuels. To assess the potential of C accumulation in NT soils, four long-term experiments (7-19 yr) in subtropical soils (Paleudult, Paleudalf, and Hapludox) varying in soil texture (87-760 g kg(-1) of clay) in agroecologic southern Brazil zones (central region, northwest basaltic plateau in Rio Grande Sul, and west basaltic plateau in Santa Catarina) and with different cropping systems (soybean and maize) were investigated. The lability of soil organic matter (SOM) was calculated as the ratio of total organic carbon (TOC) to particulate organic carbon (POC), and the role of physical protection on stability of SOM was evaluated. In general, TOC and POC stocks in native grass correlated closely with clay content. Conversely, there was no clear effect of soil texture on C accumulation rates in NT soils, which ranged from 0.12 to 0.59 Mg ha(-1) yr(-1). The C accumulation was higher in NT than in conventional-till (CT) soils. The legume cover crops pigeon pea [Cajanus cajan (L.) Millsp] and velvet beans (Stizolobium cinereum Piper & Tracy) in NT maize cropping systems had the highest C accumulation rates (0.38-0.59 Mg ha(-1) yr(-1)). The intensive cropping systems also were effective in increasing the C accumulation rates in NT soils (0.25-0.34 Mg ha(-1) yr(-1)) when compared to the double-crop system used by farmers. These results stress the role of N fixation in improving the tropical and subtropical cropping systems. The physical protection of SOM within soil aggregates was an important mechanism of C accumulation in the sandy clay loam Paleudult under NT. The cropping system and NT effects on C stocks were attributed to an increase in the lability of SOM, as evidenced by the higher POC to TOC ratio, which is very important to C and energy flux through the soil.

Imobilização de nitrogênio da uréia e do sulfato de amônio aplicado em pré-semeadura ou cobertura na cultura de milho, no sistema plantio direto

Sulfato de amônio (SA) e uréia (U) marcados com 15N foram aplicados na cultura do milho, em sucessão à aveia preta (Avena strigosa Schieb.), no sistema plantio direto, 43 dias antes e 31 dias depois da semeadura, na dose de 80 kg ha-1 de N, incorporados a 5-7 cm de profundidade, em sulcos espaçados de 0,8 m, nas entrelinhas do milho. O objetivo foi quantificar o N dos fertilizantes imobilizado no solo (15N-orgânico), no sulco de adubação, e o N-recuperado na planta nos estádios de 5-6 folhas, 11-12 folhas, florescimento e maturação fisiológica. O delineamento experimental foi inteiramente casualizado com parcelas subdivididas e três repetições. As parcelas foram constituídas das fontes U e SA, e as subparcelas, das épocas de aplicação de N. O experimento foi realizado em Latossolo Vermelho ácrico típico fase cerrado subcadocifólio, na Fazenda Floresta do Lobo-Pinusplan, em Uberlândia (MG). Na aplicação em pré-semeadura, a máxima imobilização foi observada aos 19 dias da aplicação do SA (13,3 kg ha-1 ou 16,6 % do N-aplicado) e aos 40 dias da aplicação da U (13,7 kg ha-1 ou 17,1 % do N-aplicado). A maior quantidade de N fertilizante assimilado pela planta ocorreu entre os estádios de 5-6 e 11-12 folhas (44,1 e 23,4 % do N-SA e N-U, respectivamente). Na aplicação em cobertura, a imobilização do N-SA foi inferior a 3,5 % do N-aplicado, enquanto a imobilização do N-U foi de 9,9 kg ha-1 e 7,9 kg ha-1, respectivamente, nos estádios de 11-12 folhas e florescimento. Até o estádio de maturação fisiológica da cultura, 61,8 % do N-SA e 42,0 % do N-U foram recuperados pelo milho. Em média, nos estádios de 11-12 folhas e de florescimento, para cada kg de N-SA imobilizado, as plantas de milho recuperaram 8,0 e 16,7 kg ha-1 de N fertilizante em pré-semeadura e cobertura, respectivamente. Nos tratamentos com U, a média foi de 3,1 kg ha-1, independentemente da época de aplicação. As produtividades de grãos obtidas com SA e U, independentemente da época de aplicação, foram de 7.824 kg ha-1 e 6.977 kg ha-1, respectivamente. Na adubação em pré-semeadura do milho, o SA apresentou maior rapidez na ciclagem do N imobilizado-mineralizado ("turnover"), em relação a U, e, conseqüentemente, causou maior assimilação do N pela cultura. Em cobertura, no sulco de adubação, somente houve imobilização do N-U, retardando a sua assimilação pela planta.

Impact of tillage on maize rooting in a Cambisol and Luvisol in Switzerland

Soil conditions under no-tillage (NT) are often unfavorable for the growth of maize roots in comparison to conventional tillage (CT). In 1997 and 1999, the impacts of tillage on the morphology and spatial distribution of maize ( Zea mays L.) roots at anthesis were investigated in a 5-year field trial at two sites (loamy silt and sandy loam soils) in the Swiss midlands. Four soil cores, perpendicular to the maize row, were taken to a depth of 100 cm in each plot; the root length density (RLD), the mean root diameter (MD), and the relative length per diameter-class distribution (LDD) of the roots were determined. Roots were longer and thinner in 1999 than in 1997. The RLD was significantly higher and the MD was smaller on the loamy silt than on the sandy loam. The RLD and MD decreased with the distance from the plant row. Most of the maize roots, about 80% of the total root length, were in the layer from 0 to 40 cm, with maximum values from 5 to 10 cm; the thickest roots were in the soil layer from 10 to 50 cm. Significant differences in RLD with increasing distance from the row of plants were found in the top 30 cm. Averaged over the whole soil profile, RLD was higher and MD was smaller under CT than under NT. The impact of tillage on RLD and MD interacted with spatial factors and years. Within the soil profile, RLD was significantly higher under NT than under CT at a depth of 5 cm, whereas it was higher under CT than under NT below 10 cm. Below 50 cm, there was no difference in RLD between the tillage systems. In a horizontal direction, MD was consistently higher in the row and lower in the mid-row under NT than under CT. Our results show that differences in maize root growth between tillage systems, which were reported in previous studies, persist until anthesis. The accumulation of maize roots near the soil surface in NT suggests that subsurface-banding of starter fertilizer is a more efficient way of applying fertilizer (particularly immobile nutrients such as phosphorus) compared with broadcasting in order to supply sufficient nutrients for NT maize.

Gaseous nitrogen losses and ammonia volatilization measurement following land application of cattle slurry in the mid-Atlantic region of the USA

To provide locally-determined field data for extension and environmental management purposes, gaseous N losses were measured following cattle slurry application to an arable silty-loam soil in the mid-Atlantic region of the USA. The field had been cropped to no-till maize. NH3 volatilization was measured with the micro-meteorological, integrated horizontal flux (IHF) method, and denitrification with a core incubation method using acetylene inhibition. An early-winter surface application (5 December 1996; 88 m3 ha−1 supplying 91 kg NH4+-N ha−1) was either unincorporated or immediately incorporated. NH3 volatilization was measured from the unincorporated application, and denitrification from both slurry treatments and appropriate control soils. Total NH3 loss from the unincorporated slurry application was 19% of applied NH4+-N; temperatures were cool (4–6 °C), and 25 mm of rain fell within 24 h of application. For 3 months, enhanced denitrification occurred from the two slurry treatments, with generally higher rates from the incorporated slurry. Total net denitrification loss from the surface-applied and incorporated slurry treatments was, respectively, 11 and 17% of applied NH4+-N. Denitrification loss over the winter/early-spring period was appreciable but not substantial, even where NH3 volatilization was restricted by immediate incorporation. From the spring application (30 April 1997, 39 m3 ha−1 supplying 51 kg NH4+-N ha−1), total NH3 loss was 71% of applied NH4+-N. These NH3 volatilization loss data and the similarity of climate suggest that NH3 loss factors from recent NW European work are likely to be generally applicable in the mid-Atlantic region. NH3 volatilization from the spring application was also measured using the Z-instrument (ZINST) approach, and with a system of small wind tunnels. A comparative assessment of the three methods is reported.

Effects of management practices on annual net N-mineralization in a restored prairie and maize agroecosystems

Nitrogen (N) mineralization is a spatially variable and difficult component of the N cycle to quantify accurately under field conditions. Net N-mineralization was compared by direct measurement, indirect estimate, and laboratory incubation for a restored tallgrass prairie and for deficiently and optimally N-fertilized, no-tillage (NT) and chisel-plowed (CP) maize (Zea mays L.) agroecosystems on Plano silt loam soil (fine-silty, mixed, superactive, mesic Typic Argiudoll) in Wisconsin, USA. Four years of in-situ field measurements using an incubated-soil-core/ion-exchange-resin-bag technique showed that land use significantly affected net N-mineralization. Net N-mineralization was consistently smaller in the restored prairie than in the maize agroecosystems and typically larger in the CP than in the NT maize agroecosystems. Three independent methods for indirectly estimating annual net N-mineralization (i.e., N budget residual, deficiently N-fertilized plant N uptake, and profile-scaled in-situ field measurements) were relatively consistent at capturing land-use and tillage effects on net N-mineralization. Laboratory incubation and periodic leaching of Fall-sampled soils demonstrated that both mineralized N and labile C were co-limiting factors influencing N-mineralization in agricultural soils and generally supported field measurements by showing a significant difference in net N-mineralization with and without added fertilizer-N.

Identification of suitable cultivars for organically grown maize (Zea mays) French bean (Phaseolus vulgaris L.) cropping system of Eastern Himalayas

An experiment was conducted at Umiam, Meghalaya, to assess the performance of different cultivars of maize (Zea mays L.) followed by no-till French bean (Phaseolus vulgaris L.) in cropping system mode under organic pro- duction system. During 2015, 2016 and 2017. The experiment was conducted with 10 cultivars of maize (8 com- posite cultivars and 2 local lines) followed by 10 cultivars of French bean (8 improved cultivars and 2 local variet- ies). Among all the maize cultivars evaluated over the years, maximum and minimum values of cob length, cob weight, green cob yield and kernel yield were noticed in variety RCM 1-61 and Local white respectively. Signifi- cantly higher chlorophyll index at 60 days after sowing (DAS) was recorded in RCM 1-61 followed by RCM 1-3 and minimum in RCM 1-1 followed by Hemant. Moreover, RCM 1-3 and RCM 1-2 varieties of maize recorded significantly higher crude protein content, whereas RCM 1-3 followed by Local Yellow recorded higher crude fi- bre against the other varieties of maize. The average highest yield of French bean in terms of green pod was re- corded in Naga local (8.91 t/ha) followed by RCM FB 18 (7.93 t/ha), RCM FB 19 (5.74 t/ha) and RCM FB 80 (5.73 t/ha). The maximum maize-equivalent yield (17.1 t/ha) and system productivity (6.3 t/ha) was observed for RCM 1-61 (maize cultivar)Naga local (French bean) followed by RCM 75 (maize)RCM FB 18 (French bean) sequence. The highest net returns (`2,24,059/ha) also recorded from the RCM 1-61 (maize cultivar)Naga local (French bean) cropping sequence. The soil organic carbon concentration was also enhanced after 3 years owing to adoption of maizeFrench bean cropping sequence and the highest value (21.8 g/kg) was recorded in RCM 1- 61 (maize cultivar)Naga local (French bean) sequence. The present study reveals the scope of successful culti- vation of French bean in no-till maize fallow under organic rainfed production system.

Multisensor tissue identification: the NASA smart probe project

Better methods are needed to accurately measure and record soil water content in real-time and at specified depths on a field scale. Recent developments of such a system using multisensor capacitance probes offers great potential for rigorous investigation of soil water dynamics over large areas. The purpose of this report is to show some of the kinds of information that can be obtained using this system to study the real-time soil water content dynamics at short time intervals (10 min), typically at four depth positions, under long-term, field-scale conditions, with our probes located as far as 125 m form the data logger. The systems have been used in the field for three years of continuous study (at 10 min increments), to study changes in soil water content, at four soil depths (commonly at 10, 20, 30, and 50 cm) as part of a research project to quantify temporal and spatial variation in soil properties under plow-tillage (PT) and no-tillage (NT) maize (Zea mays, L.). The multisensor capacitance probes and monitoring system have proven to be highly sensitive and robust for field scale soil water research. Viewing the soil water dynamics in real-time provides opportunity for precise control over the timing and amount of water that needs to be applied for optimal crop production yet avoiding excess deep percolation losses of water and agrochemicals to groundwater.

Measuring Agricultural Sustainability: Energy Analysis of Conventional Till and No-Till Maize in the Georgia Piedmont

The ecological sustainability of human production systems has been a major topic of discussion and study since the late 1980s. In the realm of agriculture, scholars have had difficulty identifying a whole ecosystem measure of sustainability. This paper examines the feasibility of using energy input/output analysis as a measure of agricultural sustainability, and uses such analysis to compare the efficiency of conventional and no-till farming practices. The study presents results from an experiment conducted in the Georgia Piedmont to determine the energy output/input ratios for conventional and no-till maize plots under irrigated and nonirrigated conditions. The experiment provided mixed results on whether or not no-till agriculture is a more energy efficient or sustainable agricultural practice. The authors conclude that the question as to which system is more sustainable depends on what is being measured and over what time frame. Even within the context of a short-term experiment, no-till was more efficient, hence sustainable, if total above-ground biomass production was considered. This is a justifiable approach if benefits of carbon sequestration are considered. In contrast, conventional till was more efficient in the short-term if maize kernel production alone was considered (the most important aspect to individual farmers in economic terms). Energy input/output analysis is a potentially viable measure of agricultural sustainability that deserves further study.

Measurements and Modeling of Carbon and Nitrogen Cycling in Agroecosystems of Southern Wisconsin: Potential for SOC Sequestration during the Next 50 Years

Landmanagement practices such as no-tillage agriculture and tallgrass prairie restoration have been proposed as a possible means to sequester atmospheric carbon, helping to refurbish soil fertility and replenish organic matter lost as a result of previous agricultural management practices. However, the relationship between land-use changes and ecosystem structure and functioning is not yet understood. We studied soil and vegetation properties over a 4-year period (1995–98), and assembled measurements of microbial biomass, soil organic carbon (SOC) and nitrogen (N), N-mineralization, soil surface carbon dioxide (CO2) flux, and leached C and N in managed (maize; Zea mays L.) and natural (prairie) ecosystems near the University of Wisconsin Agricultural Research Station at Arlington. Field data show that different management practices (tillage and fertilization) and ecosystem type (prairie vs maize) have a profound influence on biogeochemistry and water budgets between sites. These measurements were used in conjunction with a dynamic terrestrial ecosystem model, called IBIS (the Integrated Biosphere Simulator), to examine the long-term effects of land-use changes on biogeochemical cycling. Field data and modeling suggest that agricultural land management near Arlington between 1860 and 1950 caused SOC to be depleted by as much as 63% (native SOC approximately 25.1 kg C m−2). Reductions in N-mineralization and microbial biomass were also observed. Although IBIS simulations depict SOC recovery in no-tillage maize since the 1950s and also in the Arlington prairie since its restoration was initiated in 1976, field data suggest otherwise for the prairie. This restoration appears to have done little to increase SOC over the past 24 years. Measurements show that this prairie contained between 28% and 42% less SOC (in the top 1 m) than the no-tillage maize plots and 40%–47% less than simulated potential SOC for the site in 1999. Because IBIS simulates competition between C3 and C4 grass species, we hypothesized that current restored prairies, which include many forbs not characterized by the model, could be less capable of sequestering C than agricultural land planted entirely in monocultural grass in this region. Model output and field measurements show a potential 0.4 kg C m−2 y−1 difference in prairie net primary production (NPP). This study indicates that high-productivity C4 grasslands (NPP = 0.63 kg C m−2 y−1) and high-yield maize agroecosystems (10 Mg ha−1) have the potential to sequester C at a rate of 74.5 g C m−2 y−1 and 86.3 g C m−2 y−1, respectively, during the next 50 years across southern Wisconsin.

Genetic variation in Fusarium section Liseola from no-till maize in Argentina.

Strains of Fusarium species belonging to section Liseola cause stalk and ear rot of maize and produce important mycotoxins, such as fumonisins. We isolated two species, Fusarium verticillioides (Gibberella fujikuroi mating population A) and Fusarium proliferatum (G. fujikuroi mating population D) from maize cultivated under no-till conditions at five locations in the Córdoba province of Argentina. We determined the effective population number for mating population A (N(e)) and found that the N(e) for mating type was 89% of the count (total population) and that the N(e) for male or hermaphrodite status was 36%. Thus, the number of strains that can function as the female parent limits N(e), and sexual reproduction needs to occur only once every 54 to 220 asexual generations to maintain this level of sexual fertility. Our results indicate that the fungal populations isolated from no-till maize are similar to those recovered from maize managed with conventional tillage. We placed 36 strains from mating population A into 28 vegetative compatibility groups (VCGs). Of the 13 strains belonging to five multimember VCGs, only 2 isolates belonging to one VCG were clones based on amplified fragment length polymorphism (AFLP) fingerprints. Members of the other four multimember VCGs had an average similarity index of 0.89, and members of one VCG were no more closely related to other members of the same VCG than they were to other members of the population as a whole. This finding suggests that the common assumption that strains in the same VCG are either clonal or very closely related needs to be examined in more detail. The variability observed with AFLPs and VCGs suggests that sexual reproduction may occur more frequently than estimated by N(e).

Evaluation of the Presidedress Soil Nitrogen Test for No‐Tillage Maize Fertilized at Planting

Soil N transformations under no‐tillage (NT) could affect the utility of the presidedress soil nitrate test (PSNT), particularly where early season growing conditions are cool as in Balcarce, Argentina. The PSNT was evaluated for irrigated NT maize (Zea mays L.) with different N rates (Exp. 1) and for rainfed maize under NT and conventional tillage (CT) with different preceding crops and N rates (Exp. 2). In both experiments, N was surface broadcast as (NH2)2CO at planting. The reliability of the PSNT was evaluated when NH+4–N was determined and when samples were taken up to a 60‐cm depth in the first experiment. In this experiment, the relative yield (RY) was highly correlated (R2 = 0.61−0.86) with soil NO−3–N concentration (0–30 cm) at the six‐leaf stage (V6). The reliability (R2) did not improve when NH+4–N was determined or when sampling was done up to a 60‐cm depth. In the second experiment, there was a good relationship between the RY and NO−3–N concentration (0–30 cm) at V6 (R2 = 0.47), and the R2 value increased (R2 = 0.61) when the preceding crop was wheat (Triticum aestivum L.). Soil NO−3–N critical concentrations ranged between 17 and 27 mg kg−1 and were associated with a RY of 0.92 or higher in both experiments. The results of this study show that the PSNT can be used to evaluate preplant N applications as a complementary method to N budget in maize under different management practices.

Chemical fractionation of phosphorus, sulphur, and molybdenum in Brazilian savannah Oxisols under different land use

In soils, P, S, and Mo occur organically bound or as oxyanions. In Oxisols, oxyanions may be strongly sorbed due to the high positive surface charge. The objective of this work was to compare chemical fractions of P, S, and Mo in differently used Oxisols with similar properties in an on-farm experiment. Soil samples (0–0.15 m) were taken from three replicate plots of each of conventional tillage (CT) and no-till (NT) maize–soybean and conventional tillage sugarcane (SC) cropping systems, degraded (DP) and productive pastures (PP), Eucalyptus (EU) and Pinus reforestations (PI), and native savannah (CE). The samples were sequentially extracted with (1) 0.5 M NaHCO 3, (2) 0.1 M NaOH, (3) 1 M HCl, (4) hot concentrated HCl, and (5) concentrated HClO 4/HNO 3. In the extracts, inorganic (P i) and total P, S, and Mo were determined. Organic P (P o) was calculated as total P−P i. Total concentrations were 333–567 mg P kg −1, 231–284 mg S kg −1, and 3.2–3.9 mg Mo kg −1. The most important fractions in all studied systems were the NaOH fraction for P (38–49% of total P), the HClO 4/HNO 3 fraction for S (27–35% of total S) and the concentrated HCl fraction for Mo (86–90% of total Mo). The proportion of the more easily extracted NaHCO 3+NaOH fractions decreased along the line S>P>Mo. Fertilisation increased plant-available P and S fractions in CT and NT whereas recalcitrant fraction (concentrated HCl and HClO 4/HNO 3) remained unchanged. The P i/P o ratios in NT and CT were higher than in CE because fertiliser P mainly accumulated in inorganic P fractions. The pasture soil had lower P concentrations indicating export by grazing. Thus, 12–20 years of land use had marked effects on P, smaller ones on S, and almost none on Mo concentrations and chemical fractions.

Arbuscular mycorrhizae and the phosphorus nutrition of maize: A review of Guelph studies

The role of mycorrhizae in phosphorus nutrition of maize (Zea mays L.) is related to the fact that the P concentration in maize shoots at the four- to five-leaf stage affects final grain yield.In the early 1980s we observed greater early-season shoot-P concentration (mg g−1) and P absorption (mg plant−1) from a no-till compared to a conventional tillage system. Further studies established that the greater P absorption is due to a more effective arbuscular mycorrhizal (AM) symbiosis when the soil is not disturbed. The greater P absorption is largely a result of the undisrupted mycelium present in an undisturbed soil, rather than to increased colonization. This mycelium retains viability through extended periods in frozen soil. In the spring this mycelia network is able to acquire P from the soil and deliver it to the plant immediately upon becoming connected to a newly developing root system. Increased P absorption has not resulted in increased grain yield in field trials. Some additional factor limits yield with no-till maize preventing the advantage of early P absorption from being realized as yield. When maize follows a non-mycorrhizal crop such as canola (Brassica napus L.), mycorrhizal colonization is delayed, reducing early-season P absorption. Yield reductions may occur.In summary, AM mycorrhizae are involved in P nutrition of maize and an understanding of their functioning will assist us in modifying management practices to maximize economic returns through increased fertilizer efficiency. Key words: Maize, arbuscular mycorrhizae, phosphorus nutrition, tillage, canola