Effect of NH4-N Application Amount in Free Drainage Substrate System on the Growth and Nutrient Uptake of Chinese Chive Plants

Abstract

In order to investigate the effect of the amount of NH4-N applied (hereafter referred to as the “NH4-N application amount”) on the growth and nutrient uptake of Chinese chive (Allium tuberosum Rottler ex Spreng.) plants in hydroponic culture, seven different NH4-N application amounts using a free drainage system were examined between transplantation and harvest. To exactly evaluate the absorption of nutrients, all of the drained fluid was collected and analyzed. NH4-N was applied with irrigation once for each 1 MJ of accumulated solar irradiation per square meter. The NH4-N application amount for each irrigation event was 0, 5, 11, 21, 42, 84, and 168 μg/plant/MJ/m2 (expressed as μg/plant/MJ in this paper) respectively. The results showed that the amounts of K, Ca, and Mg taken up by the plants decreased with the increase of the NH4-N application amount. The amount of NH4-N taken up by the plants (hereafter referred to as the “NH4-N uptake amount”) increased significantly with the increase of the NH4-N application amount, while the absorption of NO3-N was not influenced. There was a significant positive relationship between the NH4-N application amount and NH4-N uptake amount, based on the law of diminishing returns. When the NH4-N application amount ranged from 0 to 84 μg/plant/MJ, the yield of Chinese chive plants increased gradually with the increase of the NH4-N application amount. The highest yield was obtained when the NH4-N application amount was 84 μg/plant/MJ. The corresponding uptake amounts of NH4-N, NO3-N, P, K, Ca, and Mg were 10.7, 14.6, 6.0, 22.5, 3.3, and 2.0 mg/plant, respectively. When the NH4-N application amount increased up to 168 μg/plant/MJ, the yield of the Chinese chive plants significantly decreased. Comparison of the results obtained in the previous and present studies suggested that the critical amount of NH4-N for the growth of Chinese chive plants should be in the range of 33–35 mg·g-1 DW, as excessive absorption damaged growth. For the cultivation of Chinese chive plants, the NH4-N uptake amount of Chinese chive plants appeared to be more important than its concentration in the nutrient solution.