of lactic acid bacteria, and the most common is Lactobacillus plantarum. Other bacteria used include Lactobacillus buchneri, Enterococcus faecium and Pediococcus species. Ryegrasses have high sugars and respond to nitrogen fertiliser better than any other grass species. These two qualities have made ryegrass the most popular grass for silage-making for the last sixty years. There are three ryegrasses in seed form and commonly used: Italian, Perennial and Hybrid. Pollution and waste The fermentation process of silo or pit silage releases liquid. Silo effluent is corrosive. It can also contaminate water sources unless collected and treated. The high nutrient content can lead to eutrophication (hypertrophication), the growth of bacterial or algal blooms. Plastic sheeting used for sealing pit or baled silage needs proper disposal, and some areas have recycling schemes for it. Traditionally, farms have burned silage plastics; however odor and smoke concerns have led certain communities to restrict that practice. Storing silage Silage must be firmly packed to minimize the oxygen content, lest it spoil. Silage goes through four major stages in a silo: Presealing, which, after the first few days after filling a silo, enables some respiration and some dry matter (DM) loss, but stops. Fermentation, which occurs over a few weeks. pH drops, and there is more DM loss, but hemicellulose is broken down; aerobic respiration stops. Infiltration, which enables some oxygen infiltration, allowing for limited microbial respiration. Available carbohydrates (CHOs) are lost as heat and gas. Emptying, which exposes surface, causing additional loss; rate of loss increases. Safety Silos are potentially hazardous: deaths may occur in the process of filling and maintaining them, and several safety precautions are necessary. There is a risk of injury by machinery or from falls. When a silo is filled, fine dust particles in the air can become explosive because of their large aggregate surface area. Also, fermentation presents respiratory hazards. The ensiling process produces "silo gas" during the early stages of the fermentation process. Silage gas contains nitric oxide (NO), which will react with oxygen (O2) in the air to form nitrogen dioxide (NO2), which is toxic. Lack of oxygen inside the silo can cause asphyxiation. Molds that grow when air reaches cured silage can cause organic dust toxic syndrome. Collapsing silage from large bunker silos has caused deaths. Silage itself poses no special danger. Nutrition Ensilage can be substituted for root crops. Bulk silage is commonly fed to dairy cattle,