Characteristics of rice stem in response to different silicon fertilizers under high nitrogen supply level

Objectives Lodging is a major limiting factor in rice production, which not only reduces rice yields but also affects the grain quality and production costs. Silicon usually plays an important role in alleviating rice lodging. The response of rice stems to silicon fertilizer application was thus investigated under two levels of nitrogen supply.

Methods A field experiment of rice (Oryza sativa japonica cv. Tang No.2) was conducted using sodium silicate (Si1) and calcium silicon fertilizer (Si2) as Si sources. The Si supply level was setup as SiO₂ 70 kg/hm², with no Si supply as control (–Si). All the Si treatments were under two nitrogen supply levels of normal N (180 kg/hm², N1) and high N (450 kg/hm², N2). The rice height, internode length, stem diameter, the leaf angles of the flag and the second leaves, stem wall thickness, and stem bending force were measured, respectively. The contents of silicon and potassium in the stalk of rice were analyzed. The anatomic structure of rice stem was also surveyed.

Results Under normal N supply level, applying Si did not show significant effects on all the tested items. Under high level supply of nitrogen, Si fertilization significantly lowered the first and the second internode length, reduced the leaf angles of the second leaf significantly by 20% (P < 0.05), increased the stem cell layers and tightness, and promoted vascular development, but did not affect the content of silicon in rice plant at the late growth stage. However, the contents of silicon in the plants were increased respectively by 14.2% at the jointing stage and by 11.3% (P < 0.05) at the maturing stage of rice under sodium silicate application, and all increased by 14.9% (P < 0.05) with calcium silicon fertilizer under high nitrogen supply level. The rice stem bending force was represented in turn by Si2, Si1, and –Si at the maturing stage of rice. Application of calcium silicon fertilizer significantly decreas the lodging-resistance index of rice (P < 0.05) by 6.2% compared with sodium silicate application. Under nitrogen supply of high level, application of sodium silicate and calcium silicon fertilizer significantly increased the rice yields by 12.3% and 12.5% compared with the treatment without Si application (P < 0.05).

Conclusions When nitrogen fertilizer is over used, silicon fertilizer application could decrease the length of the first and second internodes at the rice plant base, increase the stem cell layers and tightness, so increase the ability of rice lodging-resistance significantly and the rice yields. Under the tested soil condition, calcium silicon fertilizer demonstrates better effects than sodium silicate fertilizer under high nitrogen supply.