Land (or buildings) and managerial talent (top management) are fixed inputs in the short run.
Although there is no fixed time frame for what can be termed "short run" and "long run", generally, short run is any time duration in which a firm or business cannot make major changes or install new capital equipment to increase production. In comparison, long run is a relatively longer stretch of time during which all the inputs are variable. Fixed inputs are the input parameters that cannot be easily varied, unlike variable parameters (such as raw material or labor).
In the short run, it is not possible for a business to vary the managerial talent and/or gain new land (i.e., expand the land size or building size). These along with capital equipment are inputs that take relatively longer to be varied. It takes a long time to build a management team and hire and retain good managerial talent. Similarly, it takes time to gain land and build the infrastructure on it. Hence these are not variable inputs in the short run.
Hope this helps.