Comparative effects of app1ication of coated and non-coated urea in clayey and sandy paddy soi1 microcosms examined by the ¹⁵N tracer technique

Abstract

Nitrogen fertilizer and soil types exert an impact on plant growth. An experiment was conducted to compare the effects of application of controlled-release coated urea (CRCU) and urea on the growth of rice plants cultivated in gley (clayey) and sandy paddy soils. The ¹⁵N labeled fertilizers were applied at the rate of 8 g N m⁻² for CRCU and 10 g N m⁻² for urea. Both soil and fertilizer types significantly influenced the plant N and ¹⁵N uptake at 30 and 60 days after transplanting (DAT), with only the fertilizer type influencing the ¹⁵N uptake at 90 DAT. Sandy soil and urea increased the plant N and ¹⁵N uptake compared to the gley soil and CRCU at 30 DAT while the opposite was observed at 60 DAT, with CRCU inducing a higher ¹⁵N uptake than urea at 90 DA T. Plant ¹⁵N uptake at harvest was similar for the two types of fertilizers. Also at harvest, the average fertilizer use efficiency and proportion of unaccounted-for N for CRCU were about 74 and 25%, compared to 39 and 60% for urea, respectively. At harvest time, the total N and ¹⁵N contents in the plant parts were similar between gley and sandy soils, and between CRCU and urea, respectively, Except for the harvest index and the percentage of filled grains that were significantly influenced by the soil type, there were no significant differences in the dry weight of straw, panicle, grains, and 1,000-grains between the two soil and fertilizer types at harvest, Statistically non-significant results were obtained for the two soil and fertilizer types despite the fact that the application of CRCU in gley and sandy soils increased the values of the agronomic traits by >40% compared to urea application in the two soil types, The soil type affected the agronomic traits of rice plants much more significantly than the fertilizer type applied. Even though analysis in the absence of ¹⁵N tracer showed only minimal variations in the effects of CRCU and urea application on the agronomic traits of rice plants, the ¹⁵N analysis revealed a significant influence of the fertilizer type on the plant ¹⁵N uptake, Higher fertilizer use efficiency and a lower proportion of unaccounted-for N achieved with CRCU application resulted in a similar or in some aspects superior performance of the rice crop to that obtained with urea application, although the amount of total N applied in the CRCU treatment was 20% less than the total N amount applied in the urea treatment.

Key Words:

• controlled-release coated urea (CRCU)
• conventional urea fertilizer
• fertilizer use efficiency
• paddy soil
• proportion of unaccounted-for N