Nterpretation of Data of Stanberry & Lowrey (1965); Winter Barley, Nitrogen & Irrigation

Interpretation of data of Stanberry & Lowrey (1965); Winter Barley, Nitrogen & Irrigation


Plants are dependent on a range of essential nutrients, which are extracted from the soil by the roots. These are categorised as either macro or micro nutrients depending on the amounts required by the plant. One of the macro nutrients required for plant growth is nitrogen (Lack & Evans; 2001). Nitrogen is a component of amino acids and proteins, contributing to many structural and metabolic compounds in plants. It is a major component of chlorophyll which is required for photosynthesis, producing photoassimilates (Carbohydrates). The earth’s atmosphere is composed of 78% nitrogen (N2), however in its gaseous form nitrogen remains unavailable to plants, nitrogen is taken up by the plant roots as either nitrate (NO3-) or ammonium (NH4+). As a rule mineral nutrients taken up by the roots are transported to the shoots via the xylem and photoassimilates are transported to the roots via the phloem. In nitrogen deficient soils root growth is enhanced, in the Thornley model (1972) growth is dependent on the carbon supply from the shoots and the nitrogen supply from the roots. In principle using the Thornley model, an increase in the carbon concentrations should therefore lead to an increase in biomass partitioning towards the roots, whereas an increase in nitrogen concentrations would lead to an increase in biomass partitioning towards the shoots (Marschner, Kirkby & Cakman; 1996).
Water is one of the most important factors limiting plant growth, (Lin, Bing-Cheng & Feng-Min; 2007), in an environment with limited water there is a trade-off between reproductive growth and investment in roots to increase the water supply (Chaves, Maroco & Pereira; 2003). If the water potential of a soil drops below -1.5 MPa it causes mesophytic plants to permanently wilt. This would be best...