1975 Volume 21 Issue 2 Pages 124-135
Maximum crop growth rate (_<max>CGR) was examined for seasonal regrowth in the pure swards of alfalfa (Medicago sativa L., Du Puits) and ladino clover (Trifolium repens L., Pajbjerg Milka), grown under well fertilized and managed conditions with four times of defoliations, and the correlations of _<max>CGR and net assimilation rate (NAR) with several growth attributes in optimal LAI (_<opt>L) period were determined. NAR was expressed as the following equation revised from those of IWAKI (1958). NAR=(a-γ)-γ_n/SLA-R・(C/F)・(1/SLA)…equation (3), in the text. Here, (a-γ) is apparent photosynthetic rate of canopy leaves on leaf area basis in the daytime, γ_n respiratory rate during night canopy leaves on dry weight basis and R respiratory rate of non-photosynthetic organs on dry weight basis. Other symbols are given in the explanation of table 1. The methods for measurements of dry matter production, stratified clipping for light attenuation (extinction) coefficient (K), solar radiant flux density (S) are the same as OKUBO et al (1969). For measurement of chlorophyll content on leaf area basis (ChA), the canopy was cut with the stratified clip method into four or five layers from the top to the bottom and weighd for fresh leaf weight. Duplicate fresh materials of 2-4g were samlped for chlorophyll content, 10g for moisture content and about 10g for leaf area measurement, from which the chlorophyll content on leaf area basis (ChA), that on dry weight basis (ChW) and specific leaf area (SLA) were calculated for each of leaf layers of a canopy. For the calculation of CI, the chlorolpyll amount of each leaf layer was once determined individually, summed it to the total chlorophyll amount of leaves per unit ground area (CIL ; leaf part of CI), and added stalk chlorophll (CIS ; stalk part of CI) to the CIL into the CI for a whole canopy. The average ChA of a whole canopy leaves was determined by dividing the CIL by the LAI. Other procedures were approximately the same as BROUGHAM (1960), but the equations for chlorophyll determination by ARNON (1949) were corrected as the equation 1 in the text because there were found some slight mistakes in ARNON's equations. 1._<max>CGR attained to the highest in spring growth (exactly in June) in alfalfa and in midsummer growth in ladino clover at the value of 20 and 21g/m^2/day, respectively, among those of four seasons. _<max>CGR during autumn growth period was the lowest in both species at the value of 12.1 and 5.8g/m^2/day in alfalfa and ladino clover swards, respectively. These variations in _<max>CGR depended more on the NAR than on the _<opt>L in the growth of four seasons. Since the solar radiation for the period of _<opt>L in autumn growth was very low, one thirds of that in spring, the low values in _<max>CGR, NAR and _<opt>L also might be partly caused by the low level of the solar radiation. 2. The highest ChA among the four seasonal growth was observed in June for alfalfa sward at the value of 4.68mg/dm^2 of leaf surface and in August for ladino clover of 4.68mg/dm^2 also. The lowest was found in autumn sward at 2.94 and 2.96mg/dm for each species. This variation in ChA was closely proportional to the _<max>CGR and the NAR. 3. The _<max>CGR significantly correlated positively to ChA (r=0.93), S (0.74) and T (0.81) and negatively to C/F ratio (-0.75). The correlation coefficient of NAR with ChA only attained to significant level among the several growth attributes (table 2). Partial correlation of the _<max>CGR showed a significant value to ChA and K, and the correlation of the NAR was significant only in case with ChA (table 3). ChA showed a simple correlation significantly with S, T and C/F, and a partial correlation with S and K. 4. Photosynthetic rate under saturated light for a single leaf, taken from various depth within a canopy around _<opt>L
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