Project Leader and Principal UC Investigators
D.E. Seaman,UC Davis
The effect of nitrogen rate and time of application on performance of new
rice varieties was studied in six experiments located in different
environments. The short-stature varieties M-101, S-201, M9, M-301 and M7
were slightly more nitrogen responsive than tall varieties in 1979, but the
yield advantage of short-stature types over the tall ones was not as great
as observed in the past. The optimum time of nitrogen application depended
on total rate applied. A single preplant application was superior to split
applications when the nitrogen rate was below optimum levels. Split nitrogen
applications were superior to a single preplant application of the total
rate, however, when the rate was excessive. These results are consistent
with those of 1978. The data indicate that a single preplant application of
nitrogen is most efficient and will provide maximum yields when the
application rate is near optimum, regardless of variety (Figure 2). Split
applications, however, provided ' maximum yields when excessive nitrogen is
applied because of the inefficiency associated with nitrogen application in
water. It appears that a preplant nitrogen rate great enough to prevent
early nitrogen deficiency in rice is necessary for maximum grain yield.
Improved rice plant types, with short plant stature, greater resistance to lodging and increased nitrogen fertilizer responsiveness offer significant rice production advantages. The experimental variety 78-Y-38-41 was outstanding among the early varieties evaluated in nitrogen fertilizer trials.
The critical nitrogen values for the short-statured, nitrogen responsive varieties must be readjusted to higher values than those currently recommended for tall varieties. Tentative values have been suggested, but recent findings must be studied in detail for varietal and location effects.
The experimental Orange 6-colorimetric test for diagnosing the critical nitrogen levels in rice requires more research involving tests at different plant growth stages.
Land levelling and/or subsoiling can expose limestone hardpan material which elevates soil pH and induces zinc deficiency. The chlorosis can be corrected with zinc fertilizer, which enhances zinc uptake, plant growth and rice yields.
The short-stature M-101 and S-201 showed much greater seedling vigor and yielded significantly greater than M9 and L-201 in a calcareous soil that had a marginal zinc level. The new long-grain L-201 appeared more sensitive to the problem and developed "bronzing" symptoms which appeared to be associated with zinc nutrition.