Farm Resource Management (FRM) - College of Agricultural ...

AWATT Farm Resource Management Training ManualWEED CONTROLRotations can be used to cause shifts in weed populations. Populations of certain weed speciescan be suppressed by competition from the crop raised or by the selective use of herbicides.Wild mustard populations can be reduced by selective treatment of small grain grown inrotation with row crops. Grass weed populations, often a problem in small grains, can bereduced by the rotation with Egyptian clover.Herbicides can have both beneficial and harmful residual effects on the next crop. Therefore,planning the correct sequence of herbicide use together with crop selection has become anecessary part of rotation management.SOIL NITROGENAggressive weeds in wheat field in Baghlan Province, May 25, 2010.Legumes in the rotation can be used to increase the available soil nitrogen. Symbiotic nitrogenfixingbacteria called rhizobia form nodules on the roots of legume plants and convert or fixatmospheric nitrogen to organic nitrogen. The amount of nitrogen fixed varies with species,available soil nitrogen, and many other factors. Fixed nitrogen not removed from the land byharvest becomes available to succeeding crops as the legume tissues undergo microbialdecomposition. When the legume crop is seeded, rhizobia inoculum should always be appliedto the seed to ensure the most productive commercial strains are available to form nodulesand that inoculating bacteria are always present. Even though indigenous bacteria may bepresent in the soil, research shows improved commercial strains of rhizobia have more capacityto fix nitrogen.SOIL TILTH AND STRUCTUREMany farmers who rotate crops comment on the improvement in tilth or friability of soilfollowing soybean or other row crops. In a study involving corn, sugar beet, and barley plantedin succeeding years, soil aggregate stability was increased from 67 to 76 % when three years ofalfalfa were added to the rotation. Increased aggregate stability reduces the tendency of the soilAfghanistan Water, Agriculture and Technology Transfer Program 22