The growth curves of closed grassland swards obtained during the growing seasons of six successive years were compared with each other and with theoretical growth rates calculated by DE Wit's method and based on the mean light energy input data for the same years. The form of the growth curve consisted of a period with a constant rate, lasting for 6-7 weeks in May-June, then rapidly shortening to 3 weeks in August-September, after which there was a rather abrupt change to zero values. A comparison with theoretical values showed that a period of constant growth rate was possible, because the promoting influence of increasing LAI counteracted the effect of increasing respiration. Before the longest day this period was lengthened by an increasing daylength; thereafter the reverse was found. There is no ready explanation for the sudden decline to zero values. This is thought to be associated with changes in the rate of photosynthesis.
In 3 trials with perennial ryegrass given N in the range 0-1000 kg/ha and from 3 to 28 times/yr, DM production, N uptake and NO3 content in relation to N application rates and cutting frequencies of herbage were compared. Higher N application rates increased the herbage yield more at longer growing periods than at higher cutting frequencies. N uptake was positively affected by the application rate and not or only slightly by the cutting frequency. Consistent with this, appreciably high N conc. (max. 5.4%) were found on av. in the herbage at high fertilizer N rates and frequent cutting than at lower rates and less frequent cutting (1.6%). NO3 content increased during the growing season, especially as the N application rate was higher and the growing periods longer. (Abstract retrieved from CAB Abstracts by CABI’s permission)
Stigter, C. J., Goudriaan, J., Bottemanne, F. A., Birnie, J., Lengkeek, J. G. and Sibma, L., 1977. Experimental evaluation of a crop climate simulation model for Indian corn (Zea mays L.). Agric. Meteorol., 18:163-186.For the evaluation of a micrometeorological model, extensive measurements were taken of the microclimate in a maize cwp. Both the model and the measurements are discussed in this paper. In a comparison of the measured and simulated characteristics of the mic1·oclimate it is concluded that the absorption of radiative energy and the leaf and boundary layer resistances are adequately simulated, so that this micrometeorological model presents a sound basis for simulation models of crop production. Profiles of aerial temperature and humidity are also reasonably simulated. They can still be improved upon by a better incorporation of spatial and temporal variations of turbulence and wind as a function of the canopy characteristics, and probably by a better simulation of exchange at the soil surface. ·
Statistical treatment of yield data from potatoes, sugar-beet, peas, wheat, barley, flax and maize grown in short- and long-term experiments where water and mineral supplies were optimum showed that variations in yields, especially those of potatoes, were positively correlated with the total global radiation received during the growing period. Partial correlation coefficients showed that the length of the growing period and the annual yield increase might explain much of the yield variation.-G.M.H. (Abstract retrieved from CAB Abstracts by CABI’s permission)
The yields in kg/ha were calculated for potatoes, sugar beet and winter wheat for conditions under which water and mineral supply were not limiting growth rates. The date at which a closed crop canopy can be obtained in spring was an important criterion for the yield. Growth analyses of silage maize and sugar beet confirm that relatively high yields can be further improved by accelerating leaf development in spring. (Abstract retrieved from CAB Abstracts by CABI’s permission)
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