Crop Yield and Root System
The crop yield and quality are the final targets for crop production. In agriculture, soil treatment is one of the most important in the practice. Feeding the soil is feeding the crop. Roots as the part that directly interact with the soil particles, play an important role to the crop yield.
Root, mostly presents as a plant under the earth surface (sometimes the roots can also in the liquid solution instead of growing in the earth) organ (exceptional like mangroves’ air roots), plays extremely important roles to support the plant’s life. Providing a steady mechanical strength to the up-ground parts, up taking and transporting the nutrients, air and water, etc. Fourteen essential nutrients are various about the amount requirement. Nitrogen (N), Phosphate (P) and Potassium (K) are absorbed much greatly than Iron (Fe) or Manganese (Mn). The determining nutrient for the crop yield is N, constituting to proteins, chlorophyll, nucleic acids. The soil N naturally is from the fixation of atmospheric nitrogen by bacteria, and the decomposition of organic matter, usually decaying plant material. Around 80% of nitrogen exists in the atmosphere as the form of nitrogen gas (N2), which is unavailable for plants roots up taking. However, by the symbiotic nitrogen-fixing bacteria rhizobium invading into the leguminous plant roots, nutrients exchange between the infected roots and bacteria. The plant cortex cells provide nutrients, such as carbohydrates and energy, to the rhizobium. And the rhizobium cover nitrogen to ammonia and provide to the roots.
The main mechanisms for plant root up taking nutrients, one is directly absorption form the soil particles, accounting for only 2%, and the other one is taking the solved nutrients while water transportation. Soil pH changes the nutrients existing formation. Additionally, the pH effects on the root cells and the soil microbe’s vigor, indirectly changing the soil structure and then changing the roots growth as well. For example, in the real farming practice, liming is important for soil pH balance for crop yield. Large annually rainfalls and soils underlain by carboniferous calp limestone with shales, the soils in Ireland generally are acidic. While the ideal soil pH for most crops and grasses is at natural or slight alkaline. Liming is cost effective to increase the soil productivity, managing soils to keep them in the optimum soil pH range offers many benefits, including maintaining productive ryegrass swards and increasing the availability of major (N, P ; K) soil nutrients. Recent research from Teagasc, Johnstown Castle shows lime un-locks soil P and significantly increases the efficiency of freshly applied P. Optimum soil pH for ryegrass is 6.3 in mineral soils, increasing its persistence and productivity. The application of 5t/ha ground limestone produced similar grass yields compared to the application of 40 kg/ha P fertilizer. However, the addition of combination of lime and P fertilizer produced the largest grass yield response (1.5 t/ha more grass than the control) (D.P. Wall, 2015). However, greater pH acts negative effects to crops and animals as well. In grassland, soil pH effects greatly on the molybdenum (Mo) availability. When soil pH is above 6.2, more availability of Mo while inducing Cu deficiency for the grazing animals.
Nutrients deficiency sometimes reflected by the crops can be similar to the disease symptoms visually, such as when a plant suffering K deficiency appearing as brown scorching and curling of leaf tips as well as chlorosis (yellowing) between leaf veins. Purple spots may also appear on the leaf undersides. And the nutrient deficiencies can through altering the plant cells functions and processes to be infected. Nitrogen is greatly used for plant growing and color darkening (proteins and nucleus producing). Efficiency of N normally with the diagnoses of reducing growth and chlorosis of lower leaves. Phosphorus is important during the plant young period (for seedling and good root system developing). Reduced growth, poor root systems, reduced flowering, thin stems and browning or purpling of foliage are obvious signs for the P deficiency. Potassium is mined as a rock, which is much easier leaching than P. Shortened internodes and some burn, scorched marks in the leaves will express when K lacks. The nutrients needed is various in different crop varieties. Different nutrients are in significant required amount differences. For a specific individual, the same nutrient requirement varies during different growing stage as well. Other abiotic and biotic factors changing the amount needed, like the seasonal temperature, the seasonal precipitation. The nutrients inter-influence each other as well. It is not as much as the nutrients are provided is better for the crop growing. For example, surplus of K leads magnesium deficiency. Von Liebigs Law of the minimum points out that the plant growth (biological productivity) is limited by the scarcest resource. Greatest crop responses in yield when the limiting nutrient is met. The optimal N application is below the maximum crop yield, considering the cost efficiency for less crop-response to the N adding, avoiding more pests attracted, which the N is as the developing essential element for the pests, and avoiding N leaching and contaminating the freshwater system. To maximize the crop yield, cropping management is practical. Right source of the fertilizers needs to be match to the crop and field specific condition. Right rate of the amount of the fertilizers needed to be concerned. Right time needed to be decided to apply during the crop growth. Earlier than the optimal time applying can attract more pests and crop diseases, as well as costlier. Lastly, choosing a right place while topping the fertilizers. Overall, they all indirectly effect on the root system and in return to the crop growth.
In Ireland, a characteristic landscape of peatland, that is, the accumulation of partially decayed vegetation or organic matter, generally is not suitable for crop cultivating, like the oligotrophic bog. Except for the heavy soil structure, water logging and oxygen deficiency limit root developing, less available nutrients containing is another factor, responding to hard for the plant’s growth. Less soil microbes’ activities for the soil pores building and the organic matters decomposition and mineralization, roots relatively grow slowly. The peatlands in Ireland, including raised and blanket bogs, are beautiful and characteristic of the Irish landscape, hosting unusual assemblages of habitats. Additionally, peatlands are important to carbon sinks, contributing to carbon dioxide storage, also is a great carbon fuel source, like the coal. However, depending on the IPCC’s Peatland Sites Database in 2009 survey, turbary and mechanical cutting have resulted in a 47% loss of peatland habitats, forestry (19% loss) and agricultural (6% loss) reclamation (drainage and fertilization). In the agricultural practice, annual fertilization to bring some productivity to the land, which causes problems of freshwater eutrophication and the soil. The extinguish of peatlands causes immediate negative impacts on the hydrology and nutrient status of the host peatland, which making great peatland birds (Red Grouse, Curlew, Golden Plover, Lapwing) and other species loss. In the agricultural practice, annual fertilization to bring some productivity to the land, which causes problems of freshwater eutrophication and the soil.
In addition to cropping management strategies to improve root system function for improving agricultural productivity and minimize environmental damage, genetic study has also become a global interest. Improved root systems for soil resources using efficiently, and balancing the water, nutrients and gases absorbing, and finally contribute to increase crop yield and quality. The ideal root systems are managed for better adapted to take up the growth-limiting nutrients from the soil profiles. Longer and denser of the root hair, longer seminal roots, more lateral roots, greater biomass and steeper root angles all are the target trails of the root system. Water is the most yield-limiting soil resource on a global scale, and N is the major yield-limiting nutrient. The global climate change, such as global warming, has exacerbated the effects of water stresses on plant growth. Deeper root systems are developed for the drought resistance plants, reaching into the still-moist soil layers (Yusaku Uga, 2015). Quantitative trait locus (QTL) analyses are performed to detect the control of root traits such as root length, thickness, volume, and distribution. Then using the marker assistant selection (MAS) and PCR to breed for the improved root plants. In the wheat DRO1(which controls the gravitropic curvature in roots) experiments of Yusaku, 2015, demonstrating the modulation of root growth angle, which determines the direction of root elongation in the soil and affects the area in which roots capture water and nutrients. Plants with the DRO1 genes, such as the cultivar ‘Kinandang Patong’, meet farmer desires of higher grain yields under stressed conditions (Yusaku Uga et al. 2015).
Good root system is important to the crop yield and quality. Many factors influence the root systems, including husbandry methods, nutrients availability and the cultivar varieties. Except the importance to the agricultural economic benefits, roots contribute significantly to soil structure and nutrient maintenance as well as biomass. More scientific research to better understand the plant roots is essential and meaningful.
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