Nitrogen fertilizers (applied as nitrate, NO3-, or ammonium, NH4+) improve the amount of grain produced per acre, but nitrogen runoff and volatilization pollute the water and the air. Production of nitrogen fertilizers also uses fossil fuels. The major grain crops (such as rice and wheat) use only about 40% of the applied fertilizer—the rest is lost to the air, water, and soil microbes. Application of nitrogen fertilizers delays flowering, leaving crops vulnerable to late-season cold weather, which can impair grain filling. Traits that increase the amount of grain produced by plants and allow the grain crop to mature early will improve yields and also important for both double/triple cropping systems and for increasing the geographical range of rice into higher latitude regions. Although these traits will prove valuable for grain crops, crop breeders have had little success in this area.