Abstract
Chico, one of the low nitrate accumulating varieties, was grown in the field and the effects of fertilizing and managing practices were studied on NO3-N content in tomato fruit.
As to the effect of fertilizing, it became obvious that NO3-N content in ripe fruits tended to decrease by decreasing the amount of applied nitrogen and potash, and considerable decrease of NO3-N content was observed by increasing the amount of applied lime. Tomato fruit grown with the split application of slow-acting nitrogen fertilizer and nitrogen fertilizer containing nitrification inhibitor contained low level of NO3-N.
For the purpose of reduing NO3-N level in the soil by soil disinfection, one of the test fields was flooded during the previous winter season and drained in the early spring, and another one of the fields was sterilized with chloropicrin. As a result, NO3-N contents in the soils and those in the fruits grown in the treated fields were actually lower. It was also confirmed that the flooding practice accelerated leaching of NO3-N in the soil, and chloropicrin treatment greatly inhibited the nitrification.
Based on the above knowledge, Chico was tested as to the practical ways for reducing NO3-N content in the fruits. Chico was grown in the field which had been flooded during the previous winter season or had been previously sterilized with chrolopicrin, by fertilizing high level of lime and split application of crotonyliden diurea or ammonium sulfate with thiourea. The result obtained was satisfactory, i.e., NO3-N content in the fruit was always below 3ppm throughout the harvest season, and the fruit yield did not decrease.
The conditions of the modified cultivation to lower NO3-N content in tomato fruit described in the previous paper, i.e., “lowering NO3-N level in the fruit at the breaker stage”, and “lowering the level during the subsequent ripening process” were realized by management practice mentioned in this paper and the introduction of the low nitrate accumulating varieties.
