V. C. Baligar

Enhancing Nitrogen Use Efficiency in Crop Plants

Nitrogen is the most limiting nutrient for crop production in many of the worlds 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.

NUTRIENT USE EFFICIENCY IN PLANTS

Invariably, many agricultural soils of the world are deficient in one or more of the essential nutrients needed to support healthy plants. Acidity, alkalinity, salinity, anthropogenic processes, nature of farming, and erosion can lead to soil degradation. Additions of fertilizers and/or amendments are essential for a proper nutrient supply and maximum yields. Estimates of overall efficiency of applied fertilizer have been reported to be about or lower than 50% for N, less than 10% for P, and about 40% for K. Plants that are efficient in absorption and utilization of nutrients greatly enhance the efficiency of applied fertilizers, reducing cost of inputs, and preventing losses of nutrients to ecosystems. Inter- and intra-specific variation for plant growth and mineral nutrient use efficiency(NUE) are known to be under genetic and physiological control and are modified by plant interactions with environmental variables. There is need for breeding programs to focus on developing cultivars with high NUE. Identification of traits such as nutrient absorption, transport, utilization, and mobilization in plant cultivars should greatly enhance fertilizer use efficiency. The development of new cultivars with higher NUE, coupled with best management practices (BMPs) will contribute to sustainable agricultural systems that protect and promote soil, water and air quality.

Micronutrients in Crop Production

The essential micronutrients for field crops are B, Cu, Fe, Mn, Mo, and Zn. Other mineral nutrients at low concentrations considered essential to growth of some plants are Ni and Co. The incidence of micronutrient deficiencies in crops has increased markedly in recent years due to intensive cropping, loss of top soil by erosion, losses of micronutrients through leaching, liming of acid soils, decreased proportions of farmyard manure compared to chemical fertilizers, increased purity of chemical fertilizers, and use of marginal lands for crop production. Micronutrient deficiency problems are also aggravated by the high demand of modern crop cultivars. Increases in crop yields from application of micronutrients have been reported in many parts of the world. Factors such as pH, redox potential, biological activity, SOM, cation-exchange capacity, and clay contents are important in determining the availability of micronutrients in soils. Plant factors such as root and root hair morphology (length, density, surface area), root-induced changes (secretion of H + , OH − , HCO 3 − ), root exudation of organic acids (citric, malic, tartaric, oxalic, phenolic), sugars, and nonproteinogenic amino acids (phytosiderophores), secretion of enzymes (phosphatases), plant demand, plant species/cultivars, and microbial associations (enhanced CO 2 production, rhizobia, mycorrhizae, rhizobacteria) have profound influences on plant ability to absorb and utilize micronutrients from soil. The objectives of this article are to report advances in research on the micronutrient availability and requirements for crops, in correcting deficiencies and toxicities in soils and plants, and in increasing the ability of plants to acquire needed amounts of micronutrient elements.

The Role of Nutrient Efficient Plants in Improving Crop Yields in the Twenty First Century

ABSTRACT In the 21st century, nutrient efficient plants will play a major role in increasing crop yields compared to the 20th century, mainly due to limited land and water resources available for crop production, higher cost of inorganic fertilizer inputs, declining trends in crop yields globally, and increasing environmental concerns. Furthermore, at least 60% of the worlds arable lands have mineral deficiencies or elemental toxicity problems, and on such soils fertilizers and lime amendments are essential for achieving improved crop yields. Fertilizer inputs are increasing cost of production of farmers, and there is a major concern for environmental pollution due to excess fertilizer inputs. Higher demands for food and fiber by increasing world populations further enhance the importance of nutrient efficient cultivars that are also higher producers. Nutrient efficient plants are defined as those plants, which produce higher yields per unit of nutrient, applied or absorbed than other plants (standards) under similar agroecological conditions. During the last three decades, much research has been conducted to identify and/or breed nutrient efficient plant species or genotypes/cultivars within species and to further understand the mechanisms of nutrient efficiency in crop plants. However, success in releasing nutrient efficient cultivars has been limited. The main reasons for limited success are that the genetics of plant responses to nutrients and plant interactions with environmental variables are not well understood. Complexity of genes involved in nutrient use efficiency for macro and micronutrients and limited collaborative efforts between breeders, soil scientists, physiologists, and agronomists to evaluate nutrient efficiency issues on a holistic basis have hampered progress in this area. Hence, during the 21st century agricultural scientists have tremendous challenges, as well as opportunities, to develop nutrient efficient crop plants and to develop best management practices that increase the plant efficiency for utilization of applied fertilizers. During the 20th century, breeding for nutritional traits has been proposed as a strategy to improve the efficiency of fertilizer use or to obtain higher yields in low input agricultural systems. This strategy should continue to receive top priority during the 21st century for developing nutrient efficient crop genotypes. This paper over views the importance of nutrient efficient plants in increasing crop yields in modern agriculture. Further, definitions and available methods of calculating nutrient use efficiency, mechanisms for nutrient uptake and use efficiency, role of crops in nutrient use efficiency under biotic and abiotic stresses and breeding strategies to improve nutrient use efficiency in crop plants have been discussed.

Role of Cover Crops in Improving Soil and Row Crop Productivity

Abstract Cover crops play an important role in improving productivity of subsequent row crops by improving soil physical, chemical, and biological properties. The objective of this article is to review recent advances in cover crops practice, in the context of potential benefits and drawbacks for annual crop production and sustained soil quality. Desirable attributes of a cover crop are the ability to establish rapidly under less than ideal conditions, provide sufficient dry matter or soil cover, fix atmospheric nitrogen (N), establish a deep root system to facilitate nutrient uptake from lower soil depths, produce organic matter with low‐residue carbon/nitrogen (C/N) ratio, and absence of phytoxic or allelopathic effects on subsequent crops. Cover crops can be leguminous or nonleguminous. Leguminous cover crops provide a substantial amount of biologically fixed N to the primary crop, as well as ease of decomposition due to their low C/N ratio. Legume cover crops also possess a strong ability to absorb low available nutrients in the soil profile and can help in increasing concentration of plant nutrients in the surface layers of soil. Some nonleguminous cover crops having high N scavenger capacity compared with leguminous crops and sometimes, the growth of these scavenging grass cover crops is limited by N deficiency, growing grass/legume mixtures appears to be the best strategy in obtaining maximum benefits from cover crops.

Chapter 7 Ameliorating Soil Acidity of Tropical Oxisols by Liming For Sustainable Crop Production

Abstract The greatest potential for expanding the worlds agricultural frontier lies in the savanna regions of the tropics, which are dominated by Oxisols. Soil acidity and low native fertility, however, are major constraints for crop production on tropical Oxisols. Soil acidification is an ongoing natural process which can be enhanced by human activities or can be controlled by appropriate soil management practices. Acidity produces complex interactions of plant growth‐limiting factors involving physical, chemical, and biological properties of soil. Soil erosion and low water‐holding capacity are major physical constraints for growing crops on tropical Oxisols. Calcium, magnesium, and phosphorous deficiencies or unavailabilities and aluminum toxicity are considered major chemical constraints that limit plant growth on Oxisols. Among biological properties, activities of beneficial microorganisms are adversely affected by soil acidity, which has profound effects on the decomposition of organic matter, nutrient mineralization, and immobilization, uptake, and utilization by plants, and consequently on crop yields. Liming is a dominant and effective practice to overcome these constraints and improve crop production on acid soils. Lime is called the foundation of crop production or “workhorse” in acid soils. Lime requirement for crops grown on acid soils is determined by the quality of liming material, status of soil fertility, crop species and cultivar within species, crop management practices, and economic considerations. Soil pH, base saturation, and aluminum saturation are important acidity indices which are used as a basis for determination of liming rates for reducing plant constraints on acid soils. In addition, crop responses to lime rate are vital tools for making liming recommendations for crops grown on acid soils. The objective of this chapter is to provide a comprehensive and updated review of lime requirements for improved annual crop production on Oxisols. Experimental data are provided, especially for Brazilian Oxisols, to make this review as practical as possible for improving crop production.

Lowland rice response to nitrogen fertilization

Nitrogen deficiency is one of the most important nutritional disorders in lowland rice producing areas around the world. Nitrogen fertilizer recommendations for lowland rice (Oryza sativa L.) varieties grown on Inceptisols are limited. The objective of this study was to evaluate the response of lowland rice (cv. Metica 1) to added N and to determine N use efficiency and nutrient accumulation during the crop growth cycle. A field experiment was conducted during 3 consecutive years in the central part of Brazil on a Haplaquept Inceptisol. Nitrogen levels used were 0, 30, 60, 90, 120,150, 180, and 210 kg N ha−1. Nitrogen fertilization significantly increased dry matter and grain yield. Ninty percent of the maximum grain yield (6400 kg ha−1) was obtained with the application of 120 kg N ha−1 in the first year of experimentation. In the second and third years, 90% of the maximum yields (6345 and 5203 kg ha−1) were obtained at 90 and 78 kg N ha−1, respectively. Yield components were also significantly affected by N treatments. Among yield components, panicle length and panicle number m 2 had highest correlations with grain yield (r=0.70** and 0.78**); maximum grain yield across the 3 years was achieved at about 583 panicles m 2. Dry matter production and grain yield at the highest N level (210 kg N ha−1) across the 3 years were 9423 and 6389 kg ha−1, respectively. At this grain + straw yield, the rice crop accumulated 139 kg N, 26 kg P, 218 kg K, 36 kg Ca, 24 kg Mg, 850 g Zn, 5971 g Mn, 125 g Cu, 4629 g Fe, and 104 g B. Nitrogen use efficiency defined in several ways, decreased with increasing N rates. Agronomic efficiency across 3 yeras averaged over N rates, was 23 kg of grain produced per kg of N applied. Physiological efficiency was 146 kg biological yield (grain + straw) produced per kg of N accumulated across the 3 year and N rates. Average agrophysiological efficiency was 63 kg grain produced per kg of N accumulated in the grains plus + straw. Apparent N recovery efficiency was 39% across the 3 years and N rates. Average nitrogen utilization efficiency was 58 kg of grain produced per kg N utilized by the rice crop. Soil pH and calcium concentration in the soil decreased significantly at higher N rates, whereas, soil Al3+ level was significantly increased after the harvest of the third rice crop.

Cadmium effects on influx and transport of mineral nutrients in plant species

Abstract Solution culture experiments were conducted under controlled environmental conditions to determine the effects of cadmium(II) [Cd(II)] activity (0, 8, 14, 28, 42, and 54 μM) on influx (IN) into roots and transport (TR) from roots to shoots of zinc (Zn), copper (Cu), iron (Fe), manganese (Mn), calcium (Ca), magnesium (Mg), phosphorus (P), and sulfur (S) in ryegrass (Lolium perenne L.), maize (Zea mays L.), white clover (Trifolium repens L.), and cabbage (Brassica oleracea var. capitata L.). Shoot and root dry matter (DM) decreased with increased external Cd, and plant species differed extensively. Ryegrass and cabbage were relatively tolerant to Cd toxicity compared to white clover and maize. Influx and TR of Cu, Zn, Fe, Mn, Ca, and Mg were lower with increasing external Cd compared to controls, and species also differed. Influx and TR of P were enhanced in each species with up to 14 μM Cd, decreased in white clover and cabbage at higher Cd levels, while in maize and ryegrass continued to increase...

Fine root diameters can change in response to changes in nutrient concentrations

Plant roots function in the critical role of water and nutrient uptake. Although extensive data exist on functioning of seedling roots, little is known of the actual functionality of the fine roots of mature plants. Although this class of root represents 90% or more of the total root length of a given mature plant, their small size has inhibited detailed studies. Commonly, the critical metrics for studies of root function are root length and total weight, expressed as Specific Root Length. The metric that classifies “fine roots,” root diameter, is rarely a focus except as average diameter, even though this is the primary characteristic from which accurate estimates of surface area and volume can be calculated. Using data from several preliminary experiments, this study shows consistent changes in measured fine root diameter with changes in concentration of some nutrients. Twelve different species demonstrated concentration dependent diameter increases, or decreases, in response to increasing concentrations of nitrate, phosphorus, aluminum or tannic acid. On the other hand, Cacao (Theobroma cacao L) fine roots changed diameter in response to changes in nitrate concentration, but not ammonium. Clearly pattern of diameter change in response to nutrient concentration is dependent on nutrient, species and their interaction. It is suggested that the routine assessment of fine root diameter will be essential to understanding nutrient uptake dynamics.

Benefits and constraints for use of FGD products on agricultural land

Considerable amounts of flue gas desulfurization products (FGDs) are generated when S is recovered from coal burned at electrical generating plants to meet Clean Air standards. Beneficial uses of FGDs are continually being sought to reduce waste, decrease cost of disposal, and provide value-added products. Beneficial agricultural uses of FGDs include application as amendment to acidic soil to mitigate low pH problems (Al toxicity); provide plant nutrients (particularly Ca, S, Mg); improve soil physical properties (water infiltration, soil aggregation, particle stability); help alleviate soil compaction and improve aggregate stability of sodic soils; and inactivate P under high P-soil conditions to reduce P runoff. Co-utilization of FGDs with organic materials (manures, composts, biosolids) should also provide benefits when used on land. Constraints to use of FGDs on agricultural land could be both insufficient or excessive amounts of CaCO 3 , CaO, and/or Ca(OH) 2 to not raise soil pH sufficiently or to raise soil pH too extensively; excessive Ca to cause imbalanced Mg, P, and K in soils/ plants; Ca displacement of Al from soil exchange sites to induce Al toxicity in plants; high B to induce B toxicity in plants; excessive sulfite which is toxic to plants; and excessive amounts of undesirable trace elements (As, Cd, Cr, Ni, Pb, Se) which could potentially contaminate water and pose toxicity to plants/ animals. Most constraints are not and do not need to be problems for FGD use on land if these products are used appropriately.