The immigration enforcement action last week in this north-central Nebraska ranching community of 3,700 illuminated how important immigrant workers have become in Nebraska, particularly to the state’s largest industry, agriculture. More than 130 workers were snared in the operation, which was focused on a group that allegedly conspired to exploit, and profit from, the immigrant laborers.The raid left a shortage of workers at a local hydroponic tomato greenhouse, where 250,000 pounds of tomatoes are picked and packed each week, and at one of the state’s largest cattle feedlots, where reportedly 70,000 cattle a day are watered and fed.In rural Holt County, where the unemployment rate is 2.6 percent, the struggle to find people in a tight labor market to fill the often hard, dirty and low-paying jobs like feeding cattle or picking tomatoes has people turning to immigrants.“Labor is tough,” said rancher Kirk Shane, as he directed traffic at the Holt County Fair in Chambers. “I remember when we could hire kids for the summer. Now you can’t get them — they’re either too busy with sports or you can’t rely on them.”The “now hiring” signs outside of the O’Neill Ventures tomato greenhouse have been posted there for several weeks, and now they carry even more urgency after perhaps two-thirds of the company’s workforce was hauled away.