Use of a kernel milkline score to determine stage of maturity in maize crops harvested for silage

Abstract

A scoring system based on the position of the boundary (milkline) between the solid starch phase and the liquid phase on the surface of the maize kernel was evaluated as an indicator of crop stage of maturity. Milkline score (MLS) varies from 0 when the kernel contents are all liquid and no milkline is visible to 5 when the kernel contents are all solid and grain filling is complete. The scoring sytem is continuous in intervals of 0.5 units. The MLS was linearly related to the dry matter (DM) content of the cro in experiments at Nowra (R2 = 0.72), Wagga Wagga (R2= 0.82), and Grafton (R2 = 0.65). The predicted dry matter content at MLS 2.5 was 34.2% at Nowra, 36.0% at Wagga Wagga, and 33.7% at Grafton. Under normal seasonal conditions, milkline scoring can be used by farmers to help decide when their crops are ready for harvest. Crop DM is optimal for silage productions when MLS is in the range 2-3. However, the technique may not be reliable with severely stressed crops. Sampling 10 cobs from an area of 0.25 ha gave a 95% confidence of detecting the MLS with a precision ¦ 0.37 unit. At Nowra the milkline moved down the kernel at a rate of 1 MLS unit/9 days. This rate may be different in other environments. At the same site there was a significant (P<0.05) quadratic relationship between milkline score and DM yield, with maximum yield obtained at MLS 3.4. However, this relationship accounted for only 16.76% of the variation, and clearly, other factors influenced DM yield.