Yoshida - 1981 - Fundamentals of Rice Crop Science

More documents

Recommendations

Info

202 FUNDAMENTALS OF RICE CROP SCIENCE (b) For droopy leaves with a k value of 0.8: [1n (0.05/l.00)] F = = 3.7 . (5.10) (– 0.8) Thus, 95% of the sunlight is absorbed by the leaves in an erect-leaved rice canopy and 5% reaches the soil surface when LAI is 7.5. In a droopy-leaved canopy, a LAI of 3.7 is sufficient to intercept 95% of the sunlight. In other words, erect leaves allow the sunlight to penetrate deeper into the canopy. Because both canopies intercept the same amount of sunlight (95%), and because the erect-leaved canopy requires a greater LAI than does the droopy-leaved canopy, the erect-leaved canopy receives weaker sunlight per unit of leaf area. Consequently, the erectleaved canopy achieves greater photosynthesis. Erect leaves allow deeper penetration of incident light because they are oriented with the incident sun beams when the sun is high. For the same reason, erect leaves receive light at lower intensities than droopy leaves. The intensity of light received by the leaf surface is determined by the angle between beams of direct radiation and the normal to the leaf surface. If the angle is q° , the light intensity at the leaf surface ( I ) is related to the intensity of incident light ( I 0 ) as: (5.11) When the sun is high, flat leaves receive a higher light intensity per unit of leaf surface but for a smaller leaf area because q is close to zero. Erect leaves, however, receive a lower light intensity per unit of leaf surface but for a larger leaf area because q is close to 90°. A rice canopy in which leaves are very erect near the top and become more horizontal toward the ground reduces the foliar absorption coefficient of the upper leaves, leaving more light for the lower leaves. A mathematical crop photosynthesis model indicates that a combination of erect upper leaves and droopy lower leaves in a plant canopy gives the maximum crop photosynthesis (Duncan 1971). The LAI values necessary to intercept 95% of the incident light in rice canopies suggest that a LAI of 4–8 is needed for good rice photosynthesis. When light intensity reaches the light compensation point, there is no net gain by photosynthesis. Assuming that the light compensation point is 400 lx for a leaf temperature of 25°C and a CO 2 concentration of 300 ppm, and incident sunlight is 20 klx, at what cumulative leaf area per unit ground area ( F ) is the light compensation point reached? By equation 5.8: (5.12) (5.13) Thus, when the incident sunlight is moderate (about one-fifth of the full sunlight), the upper 10 layers of leaves in the erect-leaved rice canopy are above the light
PHOTOSYNTHESIS AND RESPIRATION 203 5.2. The influence of leaf angle distribution of a canopy on total dailygross photosynthesis at high light intensity (van Keulen 1976). compensation point. Only the upper 5 layers in the droopy canopy receive sunlight higher than the light compensation point. To get a quantitative estimate of crop photosynthesis, as influenced by LAI and leaf angle, a more complicated mathematical manipulation is needed. In crop photosynthesis models, leaf orientation is usually simplified to extreme arrangements within a canopy. In a planofile (extremely droopy) canopy, all the leaves are oriented at 0° with respect to the horizontal plane. In an erectofile (extremely erect) canopy, all the leaves are oriented at 90°. With these leaf orientations, one crop photosynthesis model (van Keulen 1976) indicates for low latitudes that: • an extremely planofile distribution gives the highest total photosynthesis at low LA1 and, • at high LA1 and high solar radiation, extremely erectofile leaves lead to a 20% increase in gross photosynthesis (Fig. 5.2). 5.1.4. Critical vs optimum leaf area index Whether there is an optimum LA1 for net dry matter production has been a widely debated subject (Yoshida 1972). The gross photosynthesis of a canopy increases curvilinearly with increasing LA1 because, as LAI increases, lower leaves are more shaded, so the mean photosynthetic rate of all leaves decreases. Net photosynthetic production, usually considered as the difference between gross photosynthesis and respiration, is determined by the nature of respiration. In early models for canopy production, respiration was assumed to increase linearly with increasing LAI and, therefore, the existence of optimum LAI was expected (Fig. 5.3). The concept of optimum LA1 was so easy to understand and looked so reasonable that it was accepted by many rice scientists. Reexamination of the relationship between LAI, respiration, and crop growth rate (Fig. 5.4) indicates that:
Page 3 and 4:
FOREWORD Rice is vital to more than
Page 5 and 6:
CONTENTS Foreword Preface GROWTH AN
Page 7 and 8:
3.2. Adaptation to Submerged Soils
Page 9 and 10:
4.5. Corrective Measures for Nutrit
Page 11 and 12:
1 .1. OUTLINE OF THE LIFE HISTORY T
Page 13 and 14:
GROWTH AND DEVELOPMENT OF THE RICE
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73 and 74:
Page 75 and 76:
66 FUNDAMENTALS OF RICE CROP SCIENC
Page 77 and 78:
Page 79 and 80:
Page 81 and 82:
Page 83 and 84:
Page 85 and 86:
Page 87 and 88:
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
100 FUNDAMENTALS OF RICE CROP SCIEN
Page 111 and 112:
Page 113 and 114:
Page 115 and 116:
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
Page 145 and 146:
Page 147 and 148:
Page 149 and 150:
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160: 150 FUNDAMENTALS OF RICE CROP SCIEN
Page 203 and 204: 5.1. PHOTOSYNTHESIS 5.1.1. Photosyn
Page 205 and 206: PHOTOSYNTHESIS AND RESPIRATION 197
Page 207 and 208: Photosynthetic characteristics Meas
Page 209: PHOTOSYNTHESIS AND RESPIRATION 201
Page 223 and 224: A traditional tall variety vs an im
Page 257 and 258: Table 7.6. An example of high yield
Page 261 and 262:
REFERENCES AGRICULTURAL POLICY STUD
Page 263 and 264:
Page 265 and 266:
Page 267 and 268:
Page 269 and 270:
Page 271 and 272:
Page 273 and 274:
Page 275 and 276:
Page 277 and 278:
show all

Yoshida - 1981 - Fundamentals of Rice Crop Science

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?