farmOS/modules/farm/farm_soil/farm_soil.module

<?php
/**
 * @file
 * Code for the Farm Soil feature.
 */

include_once 'farm_soil.features.inc';

/**
 * Implements hook_farm_log_categories().
 */
function farm_soil_farm_log_categories() {

  // Provide log categories: Soil, Tillage.
  return array('Soil', 'Tillage');
}