Effects of atmospheric ammonia (NH3) on terrestrial vegetation: a review.

Publisher Summary This chapter describes the various aspects of cereal-legume intercropping systems Intercropping is the growing of two or more crop species simultaneously in the same field during a growing season The intercropping of legumes with cereals offers scope for developing energy-efficient and sustainable agriculture The main types of intercropping include mixed intercropping, row intercropping, and strip intercropping Crop combinations differ with geographical location and there may be intercropping of tree crops, intercropping of tree and field crops, or intercropping of field crops Combinations of crops are determined primarily by the length of the growing season and the adaptation of crops to particular environments Different indices have been suggested for evaluating productivity and efficiency per unit area of land of cereal-legume intercrop systems These include comparisons of absolute yields, protein yields, caloric equivalent, and in economic terms, gross returns from intercrops and sole crops Differences in competitive ability affect the relative performance of component crops and thus the land equivalent ratio values of different cereal-legume intercrop systems It is found that phosphorus is a major nutrient that determines the production potential of most grain legumes usually intercropped with cereals

Cereal–Legume Intercropping Systems

Understanding maize–weed competition: resource competition, light quality and the whole plant

Publisher Summary A grass-legume association has been used in many countries of the world because a greater total herbage yield may be obtained by growing a grass and a legume in association, rather than in individual swards, where no fertilizer N is applied. Interferences and competition between legumes and associated grasses are of great importance in world pasture production. Such interspecific interferences are likely to be a dominating factor in the nonequilibrium, man-made and -managed pasture vegetation. It is generally accepted that grasses normally have a competitive advantage over legumes, and they tend to dominate pastures but to maintain high pasture productivity, a balance between grasses and legumes is desirable. This chapter examines the competitive relationships between grasses and legumes and also considers the way in which pasture management techniques alter the balance of legumes and grasses by manipulating the environment, which results in a competitive advantage to the legume component.

Competitive Aspects of the Grass-Legume Association

Weeds are often more competitive with crops at higher soil nutrient levels. This can result in increased de- pendency on herbicides and tiliage to maintain adequate weed control. A number of studies have shown weeds accu- mulate higher concentrations of nitrogen, phosphorus, po- tassium, calcium, and magnesium than crops, thus depleting soil nutrient levels more quickly and reducing crop yield. Understanding basic mechanisms and timing of nutrient uptake in weeds and crops can lead to fertilization strategies which will enhance the competitive ability of crops while reducing interference from weeds. Such strategies can in- clude deep band application of fertilizers to the crop row, as opposed to broadcast applications. Banding techniques also reduce the potential for nitrate contamination of surface or groundwater. The addition of nitrification inhibitors or in- creasing the proportion of nitrogen as ammonium or urea in fertilizer mixtures can restrict growth of ammonium- or urea-sensitive weeds. The timing of fertilizer applications can take advantage of maximal rates of nutrient uptake into crop roots at specific developmental stages. In addition, nutrient use efficiency can be enhanced by choosing appropriate crop cultivars, maintaining effective weed control practices, or altering row spacing or seeding rate to increase accumulation of nitrogen, phosphorus, and potassium in crops. Additional index words. Banding, competition, ecophysiology, fertilizers, nitrogen, nutrient uptake.

Approaches for Improving Crop Competitiveness Through the Manipulation of Fertilization Strategies

RECENTLY the idea has been advanced that clean cultivation of field corn is not necessary and perhaps not even desirable (2, 3, 6 j . Proponents of growing corn without cultivating, point out that the accompanying weed growth controls soil erosion and adds additional organic matter to the soil. By using a specially designed mulch planter, the usual operations in seedbed preparation of plowing, discing, and harrowing are eliminated. Although heavier rates of fertilization are required to supply the nutritional requirements of both th,corn and the weeds, the additional cost of the fertilizer is more than offset by savings made in eliminating certain tillage operations. Thus far, few investigations have been carried out to measure the added requirements of weeds for essential nutrients as well as for moisture, when growing in association with corn plants. Previous investigations by the authors ( 5 ) concerning the extent to which common weeds compete with cultural plants for essential plant nutrients, raised serious doubts in their minds about the possibility, to say nothing of the practicability, of meeting the nutritive requirements of cultural plants growing in association with weeds simply by the addition of more fertilizer. The objective of these experiments was to gather som quantitative data relative to this point, particularly with regard to varying rates of phosphate fertilization.

Plant Nutrient Competition Between Weeds and Corn1

Cation-Exchange Capacity of Plant Roots

The study of nutrient requirements of various weeds species and their relative importance as serious competitors for essential nutrients with their companion crop plants is a field that has been long neglected. Only a few references occur in the literature dealing specifically with weeds as important competitors for plant nutrients. The principal objective of this study was to determine the chemical compositon of field-collected weed species and also their companion cultural plants. The plant nutrients studied were nitrogen, phosphorus, potassium, calcium, and magnesium. Weeds commonly found in grassland, onion, corn, and potato fields were included in the investigation. Lucas, Scarseth, and Sieling ( l o ) presented analytical data indicating that the uptake of potassium by weeds was greater than that for red clover. Recently Bear et al. (2) , investigating nutrient requirements of alfalfa, found that where the available. soil potassium was low, crabgrass (Digitaria spp.) and other weeds contained much larger percentages of K than the alfalfa that was growing on the same plots. Blaser et al. ( 3 ) found that weeds in a grasslegume mixture contained more K than the grasses, and the grasses in turn contained more K than the legumes. These relationships were consistent for all treatments and for all the seasonal harvests. However, since we do not know the exact botanical composition of the species, it is highly doubtful that we are justified in attributing these properties to all the species that may be found in grasslegume mixtures. Kling, in Germany, quoted by Korsmo (9), reported the following mineral composition of weeds on a dry-matter basis: nitrogen, 2 .77445%; phosphoric oxide, 0.5-2.01%; potassium, 4.91-11.98%. Korsmo (9) also reported a very high concentration of plant nutrients for weeds in Norway. Klapp (8), in Germany, found in general that grassland weeds accumulate more P, K, Ca, and Mg than their associated grasses or legumes.

Jonas Vengris

Papers

Plant Nutrient Competition Between Weeds and Corn1

Cation-Exchange Capacity of Plant Roots

Chemical Composition of Weeds and Accompanying Crop Plants1

Use of Grass‐Killing Herbicides in Establishing Grass‐Legume Mixtures

Competition Between Barnyardgrass and Alfalfa1