Nitrogen Effects on Seedling Roots of Crucifers and Legumes

Abstract

AbstractCrucifers, like oilradish and mustard as well as the legumes pea and vetch, are often grown as catch crops. Differences in the content of soil nitrogen, left by preceding crops, may influence seedling root development. Exact observations under field conditions are difficult. For this reason, plants of the above mentioned species were grown in tubes filled with a solid soil substrate for 14 days. Nitrogen was added at six levels (mg N/100 g substrate: 0, 0.32, 0.64, 1.28, 2.56, 3.84). Shoot dry matter increased with N supply, but N concentrations of 2.56 g N and 3.84 N hindered the production of shoot dry matter. A low to medium N supply was generally optimum, while above this level of N a strong reduction in root dry matter occurred. The shoot: root ratios for pea, vetch and oilradish were minimum at a low N supply, and increased with a higher N supply. In mustard, the root surface area was reduced by any increase in N supply, while pea, vetch and oilradish had optimum values at medium N supply. Generally, the root surface area was reduced by a very high N supply. In crucifers, an initially very wide ratio of root surface area: root dry matter decreased with even a slight increase in N supply. In the legumes, a rather close ratio remained almost constant at lower levels of N supply but increased somewhat at medium and higher N levels. The length of the main root axis of the legumes had an optimum at a higher N concentration than that of oilradish while an increase in N supply always reduced the length of the main root of mustard. With the exception of pea, a very high N supply generally reduced the length of the main root. Length of lateral roots was usually retarded by nitrogen. In crucifers, a low to medium N supply increased the number of laterals markedly, whereas they were clearly reduced at a high N supply. The legumes showed no reaction to a low N supply, whereas at a high N supply the number of lateral roots increased. Implications of these results for the choice of catch crops for specific purposes are discussed.