No abstract

Conservation agriculture (CA) does have several advantages over conventional tillage (CT)-based agriculture in terms of soil health parameters. However, weeds are the major biotic constraint in CA, posing as a great challenge towards its adoption. The presence of weed seeds on the upper soil surface, due to no tillage operation, leads to higher weed infestation in CA, and so far, herbicides are the only answer to deal with this problem. Overreliance of herbicide use showed its consequence in terms of environmental pollution, weed shift and herbicide resistance development in weeds. Growing herbicide-tolerant crops using nonselective herbicides could be a broad-spectrum weed management technique to tackle weed shift, but the same is being resulted in the evolution of more problematic 'super weed'. These observations indicate the need of integrated weed management technologies involving the time tested cultural practices, viz. competitive crop cultivars, mulches, cover crops, intercrops with allelopathic potential, crop diversification, planting geometry, efficient nutrient, water management, etc., along with limited and site-specific herbicide application. The modern seeding equipment, e.g. 'Happy Seeder' technology, that helps in managing weeds through retention of crop residues as mulches, besides providing efficient seeding and fertilizer placement, shows the promise of becoming an integral part of CA system.

A model of flowing solutions that takes into account the structure, orientation, and mechanism of action of drag reducers is analyzed. For each polymer chain that causes drag reduction (DR), the model assumes the existence of two kinds of sequences that interact with the flow in different ways. The resulting solution structure seems to agree with the available experimental evidence on DR. A theoretical analysis of conformational states is provided. Computer calculations for model chains show the effects of varying solvent quality, polymer concentration, and free volume in the system. The results of the computer work provide clear criteria for choosing drag reducers with high efficacy X. The model is represented by equations in terms of the parameters that determine DR. Among other things, the theory provides a relation between the DR efficacy and time t, this for unary as well as multicomponent drag reducers. Calculations performed for a variety of DR agents in aqueous solutions show that the predicted X(t) values agree with the measured ones within limits of the experimental accuracy. The parameters obtained can be used to optimize multicomponent DR agents. While our primary interest in the present paper is in polymers, it is at least possible that nonpolymeric drag-reducing agents act by a similar mechanism.

No abstract

Weedy rice, a menace in rice growing areas globally, is biosimilar having attributes similar to cultivated and wild rice, and therefore is difficult to manage. A study was initiated to characterize the functional traits of 76 weedy rice populations and commonly grown rice cultivars from different agro-climatic zones for nine morphological, five physiological, and three phenological parameters in a field experiment under an augmented block design. Comparison between weedy and cultivated rice revealed a difference in duration (days) from panicle emergence to heading as the most variable trait and awn length as the least variable one, as evidenced from their coefficients of variation. The results of principal component analysis revealed the first three principal components to represent 47.3% of the total variation, which indicates an important role of transpiration, conductance, leaf-air temperature difference, days to panicle emergence, days to heading, flag leaf length, SPAD (soil-plant analysis development), grain weight, plant height, and panicle length to the diversity in weedy rice populations. The variations existing in weedy rice population are a major reason for its wider adaptability to varied environmental conditions and also a problem while trying to manage it.