Abstract
Relative yields and evapotranspiration (ET) of sugarcane were determined under different climatic conditions using the model PLANTGRO which was developed in Western USA. Field measurements of ET from Bhalwal, Mianchannu, Faisalabad and Bhakkar in the Punjab were used to verify the predictions. Computed seasonal ET for Bhalwal, Mianchannu, Faisalabad and Bhakkar was 122.5, 133.4, 142.5 and 150.3 cm, respectively, and was within average measured ET. Since prediction were accurate, the model can be used to aid in crop management and irrigation scheduling.
INTRODUCTION MATERIALS AND METHODS
Crops like sugarcane which are drought and waterlogging sensitive, require special water management to maintain the proper soil water environment. Methods and models are available to facilitate irrigation scheduling at farm level (Jenson et aL, 1970; Allen and Lambert, 1971). Most of these methods require a knowledge of water requirement of crop, and soil and climatic behaviour of a particular site. Crops differ for their water demand. If ET is known for a particular crop, yield can be predicted, Relationship between seasonal ET and dry matter and grain yield of many crops can be represented by a linear func-tion when irrigation scheduling is optimal (Rajput and Singh, 1986). Hanks (1974) developed a model, PLANTGRO, which used some crops soil and climate data as in-put to estimate ET and relative yield. Thus the same model, PLANTGRO, was used for this study to predict yield of sugarcane under different climatic, soil and irrigation man-agement conditions prevailing in Pakistan.
For this study, model PLANTGRO was used to predict sugarcane yields in loca-tions where the model has not been tested earlier. Different input data required in the model were collected from Bhalwal, Bhakkar, Faisalabad and Mianchannu. Values of input data with computer output for Bhakkar (as an example) are shown in Table 1. Original model is quite large (Hanks, 1974), however, a brief discussion of the parameters used is given below:
DA = AD = AF = RM -- PP =
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Length of season in days. The maximum amount of water (cm) that can be, evaporated from top layer. The ratio of relative water content in a layer below which transpira-tion will be less than potential (0.5 in the example, Table 2). The time (days) required to reach maximum root depth. A coefficient to convert relative seasonal transpiration into per cent yield (always 100).
