Potential yield of wheat in the United Kingdom: How to reach 20 t ha-1

Given the need for increased yields in wheat, new cultivars will be wanted with higher potential yield (in optimal physical environment, without weeds, pests or diseases). The aim in the United Kingdom is 20 t ha(-1). Potential yield can be predicted from the annual total solar radiation incident on the crop, the fraction of incident photosynthetically active radiation (PAR) which is intercepted, radiation use efficiency (RUE), and harvest index. The potential yield of current crops (interception of 0.46 of annual incident PAR; RUE 2.7 g MJ(-1) dry matter above ground, intercepted PAR; harvest index 0.5) was 12-14 t ha(-1) for annual solar radiation 3300-3800 MJ m(-2) which is typical across wheat-growing regions of the United Kingdom. Many combinations of increases in interception (especially retention of green leaves into August and September), RUE and harvest index would achieve potential yields of 20 t ha(-1) in sunny locations or sunny years with annual solar radiation of 3800 MJ m(-2) or above. Advancing growth duration by one month reduced yields because there was little radiation to be intercepted in March and much to be missed in July and August. If duration was advanced one month and extended by one month of maximum interception then yields were increased by around 16%. From the relationships among yield, nitrogen concentrations of grain and straw, and nitrogen supply from soil and fertilizer, yields of 20 t ha(-1) would require fertilizer application of 450-680 kg N ha(-1) for breadmaking wheat (13% protein) and 350-580 kg N ha(-1) for feed wheat (11% protein), with soil supply 100-200 kg N ha(-1) and harvest index 0.5-0.6. If nitrogen application was restricted to the N-max limit for Nitrate Vulnerable Zones (440-500 kg N ha(-1)) then 20 t ha(-1) was achievable only with soil supply well above 100 kg N ha(-1). Potential yield of wheat of 20 t ha(-1) is possible in the United Kingdom from new cultivars with improved interception of radiation, RUE and harvest index (e.g. by 17%, 32% and 18%, respectively). Improved RUE can be exploited if optimum water and nutrients are maintained throughout crop duration. Increased harvest index raises yield and reduces straw and also produces a larger yield for a given amount of nitrogen supplied. High yielding crops will require proportionate increases in nitrogen supply from the soil and fertilizer.