Soil Chemical Analysis

Worldwide, nitrogen use efficiency (NUE) for cereal production (wheat, Triticum aestivum L.; corn, Zea mays L.; rice, Oryza sativa L. and O. glaberrima Steud.; barley, Hordeum vulgare L.; sorghum, Sorghum bicolor (L.) Moench; millet, Pennisetum glaucum (L.) R. Br.; oat, Avena sativa L.; and rye, Secale cereale L.) is approximately 33%. The unaccounted 67% represents a $15.9 billion annual loss of N fertilizer (assuming fertilizer-soil equilibrium). Loss of fertilizer N results from gaseous plant emission, soil denitrification, surface runoff, volatilization, and leaching. Increased cereal NUE is unlikely, unless a systems approach is implemented that uses varieties with high harvest index, incorporated NH₄-N fertilizer, application of prescribed rates consistent with in-field variability using sensor-based systems within production fields, low N rates applied at flowering, and forage production systems. Furthermore, increased cereal NUE must accompany increased yields needed to feed a growing world population that has yet to benefit from the promise of N₂-fixing cereal crops. The Consultative Group on International Agricultural Research (CGIAR) linked with advanced research programs at universities and research institutes is uniquely positioned to refine fertilizer N use in the world via the extension of improved NUE hybrids and cultivars and management practices in both the developed and developing world. Contribution from the Okla. Agric. Exp. Stn.

https://nue.okstate.edu/Index_Publications/Improving_NUE.pdf

Improving Nitrogen Use Efficiency for Cereal Production

High variability in plant-growth response to the presence of different mycorrhizal fungi can be a major determinant of local plant species diversity. Multiple species of arbuscular mycorrhizal fungi can coexist in terrestrial ecosystems, and co-occurring plants can differ in their response to colonization by these different fungi. However, the range of mycorrhizal plant-growth responses that can occur within communities has not been determined. In the present study, I crossed a large number of plant and fungal species that co-occur to determine the range of responses that can exist within an ecosystem. I also crossed exotic fungal isolates vs. local plant isolates and local fungal isolates vs. exotic plant isolates to determine whether the range of plant growth responses differs when using foreign genotypes. The data indicate that plant growth responses to mycorrhizal inoculation within an ecosystem can range from highly parasitic to highly mutualistic. In this study, the direction and magnitude of the response depended on the combination of plant and fungal species. No plant did best with the same fungal isolate. The range of responses was greatest when using local plants and fungi. Whereas parasitic and mutualistic responses were also detected when using foreign plant or fungal genotypes, the range of responses was significantly reduced, as was the relative frequency of positive responses. Overall, this study suggests that, within ecosystems, arbuscular mycorrhizal fungi can function along a continuum from parasitism to mutualism, and that extreme responses are more common when using locally adapted plants and fungi. This high variation in plant growth response may be a large contributor to plant species coexistence and the structure of plant communities.

Variation in plant response to native and exotic arbuscular mycorrhizal fungi

Nitrogen is the most limiting nutrient for crop production in many of the world's agricultural areas and its efficient use is important for the economic sustainability of cropping systems Furthermore, the dynamic nature of N and its propensity for loss from soil‐plant systems creates a unique and challenging environment for its efficient management Crop response to applied N and use efficiency are important criteria for evaluating crop N requirements for maximum economic yield Recovery of N in crop plants is usually less than 50% worldwide Low recovery of N in annual crop is associated with its loss by volatilization, leaching, surface runoff, denitrification, and plant canopy Low recovery of N is not only responsible for higher cost of crop production, but also for environmental pollution Hence, improving N use efficiency (NUE) is desirable to improve crop yields, reducing cost of production, and maintaining environmental quality To improve N efficiency in agriculture, integrated N management strategies that take into consideration improved fertilizer along with soil and crop management practices are necessary Including livestock production with cropping offers one of the best opportunities to improve NUE Synchrony of N supply with crop demand is essential in order to ensure adequate quantity of uptake and utilization and optimum yield This paper discusses N dynamics in soil‐plant systems, and outlines management options for enhancing N use by annual crops

Enhancing nitrogen use efficiency in crop plants

Understanding how terrestrial ecosystems function requires a combined aboveground–belowground approach, because of the importance of feedbacks that occur between herbivores, producers, and the decomposer subsystem. In this paper, we identify several mechanisms by which herbivores can indirectly affect decomposer organisms and soil processes through altering the quantity and quality of resources entering the soil. We show that these mechanisms are broadly similar in nature for both foliar and root herbivory, regardless of whether they operate in the short term as a result of physiological responses of individual plants to herbivore attack or long-term following alteration of plant community structure by herbivores and subsequent changes in the quality of litter inputs to soil. We propose that a variety of possible mechanisms is responsible for the idiosyncratic nature of herbivore effects on soil biota and ecosystem function; positive, negative, or neutral effects of herbivory are possible depending upon the balance of these different mechanisms. However, we predict that positive effects of herbivory on soil biota and soil processes are most common in ecosystems of high soil fertility and high consumption rates, whereas negative effects are most common in unproductive ecosystems with low consumption rates. The significance of multiple-species herbivore communities is also emphasized, and we propose that if resource use complementarity among herbivore species or functional groups leads to greater total consumption of phytomass, and thus greater net herbivory, then both positive and negative consequences of increasing herbivore diversity for belowground properties and processes are theoretically possible. Research priorities are highlighted and include a need for comparative studies of herbivore impacts on above- and belowground processes across ecosystems of varying productivity, as well as a need for experimental testing of the influence of antiherbivore defense compounds on complex multitrophic interactions in the rhizosphere and the significance of multiple herbivore species communities on these plant–soil interactions.

Herbivore-mediated linkages between aboveground and belowground communities

Knowledge about the interactive effects of N and drought stresses on corn (Zea mays L.) root morphology and rate of N uptake is important for selecting drought tolerant and/or N efficient genotypes and for determining mechanisms that control root growth under stress. The objective was to study these interactions by growing three and four genotypes of known N utilization efficiency (NUE, kg grain/kg N uptake) responses in greenhouse and field experiments, respectively. Nitrogen application rates were 0, 30, 60, and 90 mg N kg −1 soil in the greenhouse and 0, 60, 120, and 180 kg N ha −1 in the field experiment. Water regimes included nonstress vs. an 8-d water stress in the greenhouse experiment and dryland vs. irrigation in the field []

Root Development and Nitrogen Influx of Corn Genotypes Grown under Combined Drought and Nitrogen Stresses

An improved light sensor with a spectral response based on photon absorption between 400 and 700 nm was developed for both field and environmental chamber use. The indicated sensor response was selected because it approximates the photosynthetic response of plants for which data are available. A silicon photo cell with high response in the visible range was used as a sensor. The spectral response was controlled by use of a Kodak Gelatin Wratten Filter. A visible bandpass interference filter produced a sharp cutoff at 700 nm. Heat—absorbing glass eliminated transmission beyond 1,000 nm, and a diffusing plastic and filters were mounted in a miniaturized cosine—corrected head that was fitted with a collimating system to eliminate spectral shifts which arise when light enters the interference filter at oblique angles. Error calculations indicate that under sun—and—sky radiation and various artificial light sources the errors are smaller than those associated with available standard calibration lamps. The device also includes a battery—operated meter circuit suitable for making measurements over a wide range of intensities.

Photosynthesis Light Sensor and Meter

A means of quantification of plant root branching, specifically under stress, is of importance for evaluating the contribution of plant roots to water and nutrient uptake and subsequently plant growth. An experiment was conducted to describe the morphology of corn (Zea mays L.) root systems using fractal analysis and also to determine if a root's fractal dimension (D) is altered by N stress. Corn genotypes (B73 × LH105 and N74 × Mo17) were planted in peg boxes, 1.2 m long, 1.2 m deep, and 0.05 m wide filled with 20:80 soil to sand mixture and were grown with N rates of 0, 10, 20 and 30 mg kg −1 . Thirty-nine days after planting, the mixture was gently washed from the roots and the roots were divided into nine sections (squares of side 304.8 mm) and slide photographs were taken from each section [...]

Fractal Analysis for Morphological Description of Corn Roots under Nitrogen Stress

Sorghum [Sorghum bicolor (L.) Moench] plants were grown in growth chambers at 20, 25 and 30°C in a low P Typic Argiudoll (3.65 µg P g−1 soil, pH 8.3) inoculated with Glomus fasciculatum, Glomus intraradices, and Glomus macrocarpum to determine effects of vesicular-arbuscular mycorrhizal fungi (VAMF) species on plant growth and mineral nutrient uptake. Sorghum root colonization by VAMF and plant responses to Glomus species were temperature dependent. G. macrocarpum colonized sorghum roots best and enhanced plant growth and mineral uptake considerably more than the other VAMF species, especially at 30°C. G. fasciculatum enhanced shoot growth at 20 and 25°C, and mineral uptake only at 20°C. G. intraradices depressed shoot growth and mineral uptake at 30°C. G. macrocarpum enhanced shoot P, K, and Zn at all temperatures, and Fe at 25 and 30°C above that which could be accounted for by increased biomass. Sorghum plant growth responses to colonization by VAMF species may need to be evaluated at different temperatures to optimize beneficial effects.

Effects of species of VA-mycorrhizal fungi on growth and mineral uptake of sorghum at different temperatures

Nitrogen (N) is one of the most limiting nutrients for cereal production in many areas of west Africa such as Niger. One of the strategies to improve yields is to choose crops with high N use efficiency (NUE) that can produce economic yield under limited water supply. Little information is available on comparative performance of pearl millet [Pennisetum glaucun (L.) R. Br.], sorghum [Sorghum bicolor (L.) Moench], and maize (Zea mays L.) for their NUE. A field experiment was conducted to evaluate several components of NUE for the three crop species on a Psammentic Paleustalf sand at two locations in 1997 and three locations in the 1998 rainy seasons in Niger. Nitrogen use efficiency components were calculated as incremental increases in yield per applied N or per plant N. Leaf area index and leaf chlorophyll were determined as concomitant data. Among the three cereals, sorghum and millet had greater responses to N (kg grain kg−1 N) than maize. Nitrogen use efficiency differed widely among species. Partial ...

Jerry W. Maranville

Papers

Root Development and Nitrogen Influx of Corn Genotypes Grown under Combined Drought and Nitrogen Stresses

Photosynthesis Light Sensor and Meter

Fractal Analysis for Morphological Description of Corn Roots under Nitrogen Stress

Effects of species of VA-mycorrhizal fungi on growth and mineral uptake of sorghum at different temperatures

Nitrogen fertilizer response and use efficiency for three cereal crops in niger