Publisher Summary Nitrogen, which is required in the greatest quantity of all mineral nutrients absorbed by plant roots, is an essential component of protein. The long-term strategy of nitrogen (N) use in agriculture likely will involve increased reliance on fertilizer N, biological N fixation (BNF) by leguminous crops, and wastes (including farm, urban, and industrial wastes) and their efficient management. The amounts of different nutrients absorbed by a crop from soil may vary 10,000-fold, from 200 kg of N ha-1 to less than 20 g of Mo ha-1, and yet rarely do these nutrients work in isolation. As N function in plant growth and nutrition is closely connected to C, the C=N ratio controls N availability. Nutrient interactions have a role to play in determining the course and outcome of two major issues of interest in fertilizer management—namely, balanced fertilizer input and efficient fertilizer use. The N x P (phosphorus) interaction can be termed the single most important nutrient interaction of practical significance. In addition to N, potassium (K) is the major plant nutrient absorbed and removed by crops in the largest amounts among all essential nutrients. Sulfur (S) is the fourth major fertilizer nutrient along with N, P, and K. The deficiency of S has been reported with increasing frequency in the past several years all over the world. Although Ca requirements for plant growth and metabolism are low—it has great significance in balancing levels of other nutrients—including N. Deficiencies of different micronutrients can result in a serious reduction in grain yield and quality of crops, and utilization efficiency of other nutrients and water. These include zinc, copper, manganese, iron, boron, cobalt, and molybdenum. Also, water and N are the most important factors controlling crop growth and grain production.

Interactions of Nitrogen with Other Nutrients and Water: Effect on Crop Yield and Quality, Nutrient Use Efficiency, Carbon Sequestration, and Environmental Pollution

Clubroot disease, caused by Plasmodiophora brassicae Wor, is highly damaging for Chinese cabbage The CR (clubroot resistant) Shinki DH (doubled haploid) line of Chinese cabbage carries a single dominant gene, CRb, which confers resistance to the P brassicae races 2, 4, and 8 An F2 population derived from a cross between the CR Shinki DH line and a susceptible line, 94SK, was used to map the CRb gene Inoculation of F3 families with SSI (single-spore isolate) resulted in a 1:2:1 segregation ratio Use of the AFLP technique combined with bulked segregant analysis allowed five co-dominant AFLP markers, and four and seven dominant AFLP markers linked in coupling and repulsion, respectively, to be identified Six of the 16 AFLP markers showing low frequencies of recombination with the CRb locus among 138 F2 lines were cloned A reliable conversion procedure allowed five AFLP markers to be successfully converted into CAPS and SCAR markers An F2 population (143 plants) was analyzed with these markers and a previously identified SCAR marker, and a genetic map around CRb covering a total distance of 675 cM was constructed One dominant marker, TCR09, was located 078 cM from CRb The remaining markers (TCR05, TCR01, TCR10, TCR08, and TCR03) were located on the other side of CRb, and the nearest of these was TCR05, at a distance of 192 cM

SCAR and CAPS mapping of CRb, a gene conferring resistance to Plasmodiophora brassicae in Chinese cabbage ( Brassica rapa ssp. pekinensis).

Plasmodiophora brassicae Wor. is viewed in this article from the standpoint of a highly evolved and successful organism, well fitted for the ecological niche that it occupies. Physical, chemical, and biological components of the soil environment are discussed in relation to their effects on the survival, growth, and reproduction of this microbe. It is evident that P. brassicae is well equipped by virtue of its robust resting spores for survival through many seasonal cycles. Germination is probably triggered as a result of signals initiated by root exudates. The resultant motile zoospore moves rapidly to the root hair surface and penetration and colonization follow. The short period between germination and penetration is one of greatest vulnerability for P. brassicae. In this phase survival is affected at the very least by soil texture and structure; its moisture; pH; calcium, boron, and nitrogen content; and the presence of active microbial antagonists. These factors influence the inoculum potential (sensu Garrett, 1956) and its viability and invasive capacity. There is evidence that these effects may also influence differentially the survival of some physiologic races of P. brassicae. Considering the interaction of P. brassicae with the soil environment from the perspective of its biological fitness is an unusual approach; most authors consider only the opportunities to destroy this organism. The approach adopted here is borne of several decades spent studying P. brassicae and the respect that has been engendered for it as a biological entity. This review stops at the point of penetration, although some of the implications of the environment for successful colonization are included because they form a continuum. Interactions with the molecular and biochemical cellular environment are considered in other sections in this special edition.

Plasmodiophora brassicae in its Environment

Calcium, pH and inoculum concentration influencing colonization by Plasmodiophora brassicae

Biosignature gas detection is one of the ultimate future goals for exoplanet atmosphere studies We have created a framework for linking biosignature gas detectability to biomass estimates, including atmospheric photochemistry and biological thermodynamics The new framework is intended to liberate predictive atmosphere models from requiring fixed, Earth-like biosignature gas source fluxes New biosignature gases can be considered with a check that the biomass estimate is physically plausible We have validated the models on terrestrial production of NO, H2S, and CH4, CH3Cl, and DMS We have applied the models to propose NH3 as a biosignature gas on a “cold Haber World” a planet with an N2-H2 atmosphere, and to demonstrate why gases such as CH3Cl must have too great of a biomass to be a plausible biosignature gas on planets with Earth or early-Earth-like atmospheres orbiting a sun-like star To construct the biomass models we developed a functional classification of biosignature gases, and found that gases (such as CH4, H2S, N2O) produced from life that extracts energy from chemical potential energy gradients will always have false positives because geochemistry has the same gases to work with as life does, and gases (such as DMS, CH3Cl) produced for secondary metabolic reasons are far less likely to have false positives, but because of their highly specialized origin are more likely to be produced in small quantities The biomass model estimates are valid to one or two orders of magnitude; the goal is an independent approach to testing whether a biosignature gas is plausible rather than on a precise quantification of atmospheric biosignature gases and their corresponding biomasses Subject headings: Astrobiology, Planets and satellites: atmospheres

A biomass-based model to estimate the plausibility of exoplanet biosignature gases

Under growth chamber conditions, the influence of soil moisture, soil pH, and liming sources on the germination, yield and infection of cabbage by Plasmodiophora brassicae Wor. was studied in artificially infested mineral and organic soils. Clubroot infection occurred at moisture levels as low as 9 and 60% in the mineral and organic soils, respectively. The growth of cabbage and the reduction of the incidence of clubroot were more dependent on liming source than on soil pH. Soil pH adjustment to effect complete clubroot control was invariably deleterious to cabbage growth. It was established for the organic soil that the effect of calcium hydroxide was important in correcting soil acidity as well as supplying calcium as an essential plant nutrient for cabbage. In addition, there was evidence that correction of the soil acidity favored clubroot development, but simultaneously the Ca ion had an inhibitory effect on the disease organism. On the mineral soil, Mg sources producing a soil pH not normally consid...

INFLUENCE OF SOIL MOISTURE, SOIL pH, AND LIMING SOURCES ON THE INCIDENCE OF CLUBROOT, THE GERMINATION AND GROWTH OF CABBAGE PRODUCED IN MINERAL AND ORGANIC SOILS UNDER CONTROLLED CONDITIONS

Vegetable response to fertilizer treatments of a well decomposed organic soil over a 4-yr period showed potassium as the primary nutrient to be first in short supply for celery (Apium graveolens L....

N–p–k fertilizer effects on yield, composition and residues of lettuce, celery, carrot and onion grown on an organic soil in quebec

Crop successions involving carrot (Daucus carota L.), onion (Allium cepa L.) celery (Apium graveolens L.) and lettuce (Lactuca sativa L.) were organized to study the effect of each crop on the yield of the subsequent crops when grown on an organic soil. Crop sequences affected yields significantly. Carrot yields were significantly greater when they followed celery or lettuce than when they followed carrot or onion. Onion yields were greatest after celery or lettuce, less after onion, least after carrot. Celery yields were greatest after celery or lettuce, less after onion, least after carrot. Lettuce yields were greater after lettuce or celery than after onion or carrot. The nematode species occurring in the largest numbers after continuous growing of carrot, onion, celery, and lettuce were Meloidogyne hapla, Paratylenchus hamatus, Pratylenchus penetrans and M. hapla, respectively.

Carrot, onion, celery and lettuce crop succession studies on an organic soil

The response of timothy in monoculture and m association with each of alfalfa and birdsfoot trefoil was studied when root zone temperatures of 10, 18.3 and 26.7 C were imposed on a soil receiving N at 0 and 100 pp2m of soil in all possible combinations with K at 0 and 166 pp2m of soil. The different plant associations resulted in highly significant differences in yields, irrespective of soil temperature or nitrogen addition, but only at 10 C was there a significant interaction between K and the plant associations. The legumes associated with timothy had a significant effect on timothy yield at all temperatures, and the behavior of the different legumes was in turn differently affected by fertilizer nutrients as well as by different temperatures. Shoot to root ratios of timothy tended to be greater when associated with trefoil than with alfalfa at all soil temperatures. The effect of soil temperature and fertilizer varied for alfalfa vs. trefoil when either was grown with timothy.

Influence of nitrogen, potassium and root zone temperature on the response of timothy in monoculture and in association with alfalfa and birdsfoot trefoil

Herman A. Hamilton

Papers

INFLUENCE OF SOIL MOISTURE, SOIL pH, AND LIMING SOURCES ON THE INCIDENCE OF CLUBROOT, THE GERMINATION AND GROWTH OF CABBAGE PRODUCED IN MINERAL AND ORGANIC SOILS UNDER CONTROLLED CONDITIONS

N–p–k fertilizer effects on yield, composition and residues of lettuce, celery, carrot and onion grown on an organic soil in quebec

Carrot, onion, celery and lettuce crop succession studies on an organic soil

Influence of nitrogen, potassium and root zone temperature on the response of timothy in monoculture and in association with alfalfa and birdsfoot trefoil