Effects Of Nitrogen Supply Research Articles

Effect of nitrogen supply on the response of Majestic potato to gibberellic acid

SUMMARYPotato plants sprayed with gibberellic acid (GA) were given extra nitrogen either through the soil (as ammonium nitrate) or through the leaves (as urea). GA increased the initial production of dry matter but the effect did not persist, even with additional N. The number of leaves on lateral branches was decreased by GA partly because leaf production on laterals at lower nodes was inhibited. N increased the rate leaves were produced on lateral branches; the soil application doubled the leaf number and the urea increased it by 50%. GA, but not N, increased the area of a main‐stem or lateral‐stem leaf; however, nitrogen produced the largest total leaf area because it produced more leaves. There was no evidence for any interaction between GA and N either in the effect on leaf number or total leaf area. The fall in total N content per unit area caused by GA found in an earlier experiment was confirmed and additional N did not arrest this decline. Loss of efficiency of GA‐sprayed plants is unlikely to result from indirect deficiency caused by rapid leaf expansion.

GROWTH AND NUTRITION OF TIMOTHY (PHLEUM PRATENSE L.)

During the first year of growth of timothy, variations in nitrogen supply affected the number of tillers and leaves, leaf area and dry weight, but had little influence on relative growth and net assimilation rates, except at very low levels of nitrogen. Differentiation and ear emergence occurred slightly earlier at high nitrogen and ear length was increased; there was also an increase in the proportion of fertile tillers among the total number produced after the first few weeks of tillering. The effect of nitrogen supply on the number, dry weight and ear length of early primary tillers was small but became larger in later tillers. Irrespective of the level of nitrogen supply, tillers had particularly high net assimilation rates during the first few weeks following their appearance.

Effects of nitrogen supply for the various stages of growth on the yield and quality of potato tubers

Experiments were carried out to clarify the effects of nitrogen supply for the various stages of growth on the yield and quality of potatoes (var. Irish Cobbler) in the sand culture. Seed potatoes were planted late in March (1955) or early in April (1956), and plants were harvested early in July (1955) or middle in July (1956). The concentration of nitrogen in the solution was 140 ppm and other nutrient elements also were supplied sufficiently. The results obtained are as follows. (1) The emergence of tubers in the minus nitrogen treatment was delayed five days compared with that of the control treatment in 1955. But the difference between both treatments was only two days in 1956 experiment, in which larger seed potatoes were used (seed weight was 42_??_43g in 1955, while about 110g in 1956). (2) In both years, plants which were withheld nitrogen supply after late in June (almost ceasing stage of top growth) showed earlier yellowing of ower leaves, but their yields did not fall behind the control plants supplied with nitrogen throughout all stages of growth. But, when nitrogen supply was discontinued after late in May (begining stage of tuber thickening), or early in June (vigorously growing stage of both top and tubers), yield decreas-ed considerably. On supplying with nitrogen after early in May (completing stage of emergence), top growth caught up soon with that of the control, but tuber yield did not reach. And yield of plants supplied with nitrogen during the period between early in May and late in June, was almost the same as the yield of the control plants. Further, nitro-gen supply being delayed till late in May, yield lowered considerably. (3) As to tuber quality, there were no distinct differences in dry matter percentage among the treatments But, in ascorbic acid and total nitrogen, the earlier nitrogen supply was discontinued, or the later nitrogen supply was delayed, the lower were their contents. In conclusion, the period most needed for nitrogen in this experiment, was between early in May (30_??_40 days after planting) and late in June (about 80 days after planting), and nitrogen supply from planting to emergence was also effective for yield increase. But nitrogen supply after late in June was not effective.

Morphorgical and Physiological Studies on Nodule Formation in Soybean : (I) Relation between nitrogen over supply and nodule formation

This experiment has been carried out in order to clarify the effects of nitrogen supply on soybean plants to nodule formation. Particular attention is given to the mechanisum of inhibition on nodule formation by nitrogen over supply. 1) The nodule formation was inhibited with an accompanying increase of nitrogen supply and it indicated on nodule numbers and nodule weight per plant during the growing period. 2) Different nitrogen, levels in host tissues and culture media have no effect to activety and the penetration of Rhizobium japonicum (Table. I). 3) The nitorgen over supply induced higher concentration of total nitrogen and lower concentration of total suger and reducing suger in soybean root. Auther conclude that the reducing suger levels of host tissues control the nodule formation.

INFLUENCE OF NITRATE SUPPLY UPON THE ASCORBIC ACID CONTENT OF TOMATOES

THE APPLICATION of nitrogen fertilizer has been reported to lower the ascorbic acid content of various crops (Hamner and Maynard, 1942; Maynard and Beeson, 1943-44; Somers and Beeson, 1948, for reviews; also Jones and Parker, 1947). Hamner et al. (1945) reported that the ascorbic acid content of tomatoes from field plots which received fertilizer containing large amounts of nitrogen (2020-10) was about 20 per cent less than from comparable plots which received a fertilizer containing no nitrogen (0-20-10) at the same rate. In sand culture, however, Hamner et al. (1942) failed to find any effect of nitrogen supply upon the ascorbic acid content of tomatoes. Other instances where the amount of nitrogen applied failed to influence significantly the ascorbic acid content of plants are cited by Somers and Beeson (1948). In some cases these different findings may result from the nitrogen source used. Nitrate and ammonium sources of nitrogen supply under suitable conditions may have quite different effects upon the ascorbic acid content of plant tissues (Sideris and Young, 1945; Somers and Kelly, 1950). The following experiment was undertaken to study in more detail the physiological basis for the influence of the amount of nitrogen supplied to tomato plants upon the ascorbic acid content of the ripe tomatoes produced. MATERIALS AND METHODS.-Tomato seed (variety Bonny Best) was planted in sand April 7, 1945, and was watered for 1 week subsequently with Hoagland Solution No. 1 diluted 1:5 (Hoagland and Arnon, 1938). Throughout the rest of the experiment the plants were watered with full strength Hoagland solution except as indicated in table 1. The plants were transplanted to 2 gal. crocks of sand May 6, where they were watered once a day with Hoagland solution and flushed once a week with distilled water. All of the plants were allowed to grow in the greenhouse until June 21, when they were moved outside and were tied to tall stakes. They were pruned to a single stem by frequent removal of the lateral buds. Upon being moved outside the plants were arranged in two blocks of thirty-six plants each. Each block contained six treatments with six plants in each, and the plants were spaced so that they shaded each other very little, if any. The various treatments differed from each other in the amount of nitrate which was supplied to the plants at various periods during the experiment. They are summarized in table 1. The greatest nitrate supply, 15 me./l., was that obtained by using full strength Hoagland solution. The lower rates of nitrate suip-

Effects of Nitrogen Supply on Rates of Photosynthesis and Respiration in Plants

On the basis of the foregoing data it is evident that the composition of any given plant is in a marked degree correlated with its respiratory activity. Thus tomato plants very high in carbohydrates but low in their nitrate or soluble nitrogen content may have a relatively low respiratory rate, whereas one which is higher in its nitrate content will have an appreciably higher one. Or any given plant high in its carbohydrate reserves will have its respiratory rate increased if nitrates are supplied to it in abundance, other conditions remaining the same. Although all the plants used in the various experiments were very high in reserve carbohydrates, a relatively slight change in the amount of this reserve had a great effect upon the time required for nitrates to make their appearance in the tops of the plants after they had been applied in the nutrient solution. In every case the addition of nitrates to plants high in reserve carbohydrates caused an increase in respiration, the greater such reserve the mor...