A field experiment was conducted to investigate the dynamics of ammonium nitrogen (NH 4 +-N) in the soil during an entire ricegrowing season. The NH 4 +-N dynamics were measured in paddy soils from two N application methods, namely, urea deep placement (UDP) and broadcast prilled urea (PU). The pore water samples from a 10 cm soil depth were collected using a "rhizon sampler." The samples were collected at 0, 7, 10, 14, 20, and 22 cm from the urea briquette (UB) placement point at 7, 14, 21, 35, 64, and 83 days after transplanting (DAT) of rice. The NH 4 +-N in the floodwater sample was measured for a week after each split application of PU. UDP retained NH 4 +-N at the placement site (7-10 cm depth) until 64 DAT. A small amount of NH 4 +-N moved horizontally up to 14 cm from the placement site. It's movement to the soil surface and floodwater was very low to negligible. In contrast, PU produced more NH 4 +-N in both the floodwater and in the soil surface. Therefore, broadcast urea had significantly (p < 0.05) higher ammonia volatilization (~15% of applied N) compared to UDP (<1%). UDP significantly (p < 0.05) increased grain yields, N uptake, and N recovery compared to broadcast urea. These results confirm that a single application of UDP could meet plants' N demand throughout the rice-growing period, particularly for short-and medium-duration rice varieties.

Pomegranate (Punica granatum L.) is one of the most important fruit trees in semi-arid land. Previous studies were primarily focused on soil microbial community composition under different pomegranate plantation managements. However, soil microbial community composition under long-term pomegranate plantation has rarely been studied. We investigated pomegranate plantation along with an age sequence (i.e., 1, 3, 5, and 10 years after pomegranate plantation; abbreviated by P1, P3, P5, P10, respectively) in the Middle Yellow River floodplain. Our objectives were to address (1) variations of soil physicochemical properties and (2) changes in soil microbial community composition and the influential factors. The results demonstrated that the soil water content of pomegranate plantation decreased with the increase of pomegranate plantation stand age. Specifically, dissolved organic carbon, ammonium, and available phosphorus increased significantly with stand age both at 0–10- and 10–20-cm soil depths. The P10 had the highest microbial phospholipid fatty acid (PLFA) profiles, including fungi, bacteria, Gram-positive bacteria, Gram-negative bacteria, and arbuscular mycorrhizal fungi. The ratio of fungal PLFAs to bacterial PLFAs increased and the ratio of Gram-positive to Gram-negative bacterial PLFAs decreased along the pomegranate plantation stand age. Dissolved organic carbon was the most important influential factor among the studied variables, which explained 42.2% variation of soil microbial community. In summary, the long-term plantation of pomegranate elevated soil microbial biomass and altered microbial community composition.

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