Crop residues are an important source of nitrogen (N) for rice
(Oryza sativa L.). The objective of this research was to
determine how the supply of mineral N from different prior crops or fallow
might affect the growth and yield of rice. The study also tested whether N use
by rice might be improved by timing the application of inorganic fertiliser N
to supplement the N mineralised after prior crops. Experiments consisted of
fallow, or cereal or legume crops in the dry-season followed by wet-season
rice; and fallow, or cereal or legume crops in the wet- season followed by
dry-season rice. Urea at one-third of the rate required for optimum rice yield
was applied at 3 times during the rice crop: sowing, permanent flood,
and/or panicle initiation. The prior fallow and crop treatments
significantly influenced the growth and yield of rice crops. After a fallow,
the pattern of soil N mineralisation promoted vegetative growth but was
limiting during grain-filling. In contrast, after a cereal crop, rice
vegetative growth was limited but grain-filling was promoted. Legume prior
crops promoted both vegetative and grain growth. The benefits derived from
growing the cereal or legume crops before rice, in terms of replacing
fertiliser N, were dependent on the time at which fertiliser N was applied to
the rice crop. In particular, legume crops frequently nullified the rice
growth responses to fertiliser N. The results demonstrated that fallow and
prior crops can alter the amount and timing of mineral N supply to a rice
crop. Farmers should consider including a legume crop in rotation with rice
because legumes supply N, which increases rice yield and reduces the
requirement for fertiliser N. Cereal crops also contribute N, although farmers
who use a cereal rotation should monitor the soil and crop N status during
early rice growth, and supply extra fertiliser N to alleviate N deficiency.
Improving rice growth and yield with silicon addition in Oxisols
