The practical adaptability of a formula for estimating the amount of absorbed nitrogen (absorbed nitrogen (g/m2/14 days)=increased leaves (no./m214 days) ×0.0383+1.856) was tested as a fertilization index in autumn cucumber, cultivated using drip tubes, in a commercial greenhouse. Ammonium nitrate and potassium nitrate were used as nitrogen sources.
First, the total applied nitrogen was -1.8kg/a on both sides of the greenhouse. The final marketable yields were 543-615kg/a, i. e., the same as those produced by means of conventional cultivation, although markedly less nitrogen fertilizer was used. The NO3-N level in the soil was kept under 20mg/100g throughout the period. No nitrogen remained in the soil because fertilization was stopped one month before the end of harvest.
Second, the distribution of EC and pH throughout the field was estimated. The variation of the EC distribution may have been due to unequal nitrogen application before the introduction of drip fertilization, which improved distribution. Conversely, drip fertigation did not improve the variation in pH, because no basic elements were applied in this system.
In conclusion, our formula should be used to estimate the amount of nitrogen to apply. This saves fertilizer, while providing sufficient yields and controlling the unequal distribution of EC in autumn cucumber raised using drip tubes.
