Effects of pre-harvest and post-harvest factors on grain hardness and stress cracking in three maize hybrids

The effects of several pre-harvest factors (hybrid, nitrogen, harvest grain moisture content) and post-harvest drying factors (drying temperature and relative cooling rate) on grain physical attributes and stress cracking were investigated. While the proportion of hard endosperm. (H/S ratio) increased in all three hybrids with nitrogen application, the effects of nitrogen on grain hardness and drying rates were small. Stress cracking and the stress crack index (SCI) in grain were significantly affected by the main effects of hybrid, nitrogen, harvest moisture, drying temperature and cooling rate. As drying temperature increased from 50degreesC to 80degreesC, the percentage of grains with multiple and checked stress cracking increased. As cooling rate reduced from 1.11 to 0.23 degreesC/degreesC/minute x 10(-2), the numbers of sound grains (non-stress cracked grains) significantly increased. At the lowest cooling rate of 0.23 degreesC/degreesC/minute x 10(-2), checking was minimal and less than 15% of the grains had multiple stress cracks. Prediction curves indicated that hybrid P3902 had the lowest SCI among the three hybrids, the SCI being around 205 at 0 kg N/ha and 240 at 230 kg N/ha, respectively. The SCI value for hybrids Furio and P3753 was more than 300 irrespective of nitrogen. Stress cracking in grains was affected more by cooling rate than any other factors.