Inhibition of nitrogen uptake by rice after wheat straw application determined by tracer NH₄⁺-¹⁵N

This experiment was carried out to determine whether the delay in rice growth associated with wheat straw application, especially at the early stage, was due to the acceleration of N assimilation or N uptake inhibition. Tracer ¹⁵N was used for rice plants cultivated in pots. After 24 h of tracer application the plants and soils were sampled for analysis. Seventeen days after transplanting, N uptake of rice decreased and the amount of unavailable tracer remaining in soil increased by wheat straw application. At the booting stage, 6 d before heading, N uptake was larger and the amount of remaining tracer was lower in the plots in which wheat straw was applied than in the control. It was obvious that the decrease of N uptake by wheat straw application was caused by N uptake inhibition and not by N starvation for a period of time at the early stage. The inhibition was removed at the booting stage.