Yoshida - 1981 - Fundamentals of Rice Crop Science

164 FUNDAMENTALS OF RICE CROP SCIENCE
Table 3.31. Effect of sulfur on dry weight of tops and sulfate-S, organic-S, total-S, and
percent dry weight of blade-3 from greenhouse (GH) and outdoor (OD) alfalfa. Means
of 5 replications. a
Dry wt
Blade-3
Sulfate
S
(mg)
0
20
40
80
120
160
320
640
1280
2560
Tops Blade-3 Greenhouse Outdoors
GH OD GH OD SO 4 -S Organic-S Total-S SO 4 -S Organic-S Total-S
(g) (g) (%) (%) (ppm) (ppm) (ppm) (ppm) (ppm) (ppm)
2.1 7.2 20.5 17.6 44 700 750 156 1240 1400
22 26 20.9 18.4 49 990 1040 113 1240 1350
39 38 20.9 18.8 44 1130 1170 100 1380 1480
61 63 21.5 20.6 57 1500 1560 98 1580 1680
64 73 21.7 20.8 96 2300 2400 113 1740 1860
70 79 20.4 19.5 210 2610 2820 150 2380 2530
81 91 20.8 19.6 1250 3430 4690 840 3120 3960
75 93 20.9 20.5 1870 3500 5370 1540 3420 4970
78 89 21.3 20.7 2070 3100 5170 1680 3340 5020
70 91 19.8 20.1 2080 3320 5400 1780 3410 5190
a Ulrich et al (1967).
from cars, and burning of disposed materials release sulfur oxide into the atmosphere.
The sulfur may be absorbed directly through the leaves, be dissolved in
rain water, fall onto the ground, and be absorbed through the roots. Radioactive
sulfur has been used to show that the plant can absorb SO 2 through its leaves
(Thomas et al 1944).
To illustrate the importance of atmospheric sulfur as a sulfur source for plants,
alfalfa plants were exposed to unfiltered air and to air filtered through thin beds of
activated carbon (Table 3.31). Air-borne sulfur was absorbed by alfalfa, resulting
in a significant increase in growth and in the concentration of sulfate S and organic
S when the sulfur supply was low.
The amount of sulfur brought by precipitation ranges from 0.1 to 140 kg/ha per
year (Fried and Broeshart 1967). The large amount of sulfur in precipitation comes
primarily from burned fossil fuels, particularly in industrial centers where SO 2
and other gaseous sulfur compounds are continuously released into the atmosphere.
The quantities of sulfur in precipitation in rural areas are usually low.
3.13.4. Critical sulfur content and critical N-S ratio at different growth
stages
Two critical levels can be graphically defined (Fig. 3.29): the critical sulfur
content and the critical N-S ratio in plant tissues required to obtain maximum dry
weight (DC 100 ), and the critical sulfur content and the critical N-S ratio in plant
tissues to obtain 50% of the maximum dry weight (DC 50 ). The critical sulfur
content in straw for the maximum dry weight vanes from 0.16% at the tillering
stage to 0.07% at flowering and to 0.06% at maturity (Table 3.32).