The estimation of crop water use is critical for accurate irrigation scheduling and water licenses. However, the direct measurement of crop water use is too expensive and time consuming to be performed under all possible conditions, which necessitates the use of water use models. The FAO-56 procedure is a simple, convenient and reproducible method, but as canopy cover and height vary greatly among different orchards, crop coefficients may not be readily transferrable from one orchard to another. Allen and Pereira (2009) therefore incorporated a procedure into the FAO-56 approach which estimates crop coefficients based on a physical description of the vegetation and an adjustment for relative crop stomatal control over transpiration. Transpiration crop coefficients derived using this procedure and fixed values for citrus, did not provide good estimates of water use in three citrus orchards. However, when mean monthly leaf resistance was taken into account, 1 good agreement was found with measured values. A relationship between monthly reference evapotranspiration and mean leaf resistance provided a means of estimating mean leaf resistance which estimated transpiration crop coefficients with a reasonable degree of accuracy. The use of a dynamic estimate of mean leaf resistance therefore provided reasonable estimates of transpiration in citrus.

Subtropical fruit crops form an important part of the fruit industry in many countries. Many of these crops are grown in semi-arid regions or subtropical regions where rainfall is seasonal and as a result the vast majority of these perennial, evergreen orchards are under irrigation. This represents a significant irrigation requirement and with more emphasis being placed on the conservation of water and orchard profitability, it is becoming increasingly important to accurately estimate water use of these crops and schedule irrigation accordingly. The FAO-56 procedure is a simple, convenient and reproducible method for estimating water use. However, the transferability of crop coefficients between different orchards and growing regions is not always readily achieved, due largely to differences in canopy size and management practices. In addition, as subtropical crops tend to exhibit a higher degree of stomatal control over transpiration than most other agricultural crops, some measure of canopy or leaf resistance must be taken into account when using models based on atmospheric demand. The challenge is therefore to provide reliable and dynamic estimates of canopy resistance from relatively simple parameters which can be of use to irrigation consultants and farmers for determining the water requirements of these crops. The challenge remains to ensure that these dynamic estimates are realistic and readily applicable to a number of growing regions. The derivation of transpiration crop coefficients, based on canopy cover and height and a dynamic estimate of leaf resistance, provided reasonable estimates of transpiration in three orchards in contrasting climates, suggesting that this approach could prove useful in future for subtropical crops.

No abstract

Maternal season defined, as the prevailing environmental conditions during crop growth has been known to influence not only grain yield but also seed quality. A laboratory and field experiment were conducted in October 2014, to determine the influence of total rainfall and mean monthly temperature on germination, vigor and emergence of sorghum seeds which were harvested from three different seasons and were kept under controlled conditions. The laboratory experiment was a 3 x 3 factorial experiment laid in completely randomized block design (CRD) replicated three times. The first factor was variety (Macia, SDSL 89473 and Sima), the second factor was growing season (2004/5, 2006/7, 2007/8). A field experiment was carried out to investigate the emergence of seed materials used in the laboratory experiment. The experiment was a 3 x 3 x 3 factorial treatment structure laid out in a Randomized Complete Block Design (RCBD) with the third factor being sowing depth at 5.0, 7.5 and 10.0 cm. Seedling emergence was observed at 10 days after sowing. In the laboratory experiment it was observed that there was no significant difference (P>0.05) on the effects of season and variety on germination of seeds. However, there was significant difference (P<0.001) on seed vigor due to variety under laboratory conditions. For the

No abstract