The combination of optimal crop sowing terms and component composition are important factors that influence the growth, development and productivity of plants in compatible crops. One of the problems in growing corn and sweet sorghum in compatible crops is that the wax ripeness of grain in the sorghum occurs 7–10 or more days later than corn. Therefore, it is possible to achieve practically simultaneous harvesting these crops in the phase of wax ripeness of grain by choosing late-maturing corn hybrid (FAO 500) or by shifting the sowing terms in compatible crops with sweet sorghum.

The aim of the research was to determine the effect of sowing terms on crop growth, development, interphase periods duration and corn productivity in compatible crops with sorghum. The research was carried out in 2014–2016 in the experimental field of the Bila Tserkva National Agrarian University with the following terms of corn sowing:
1. Simultaneously with sweet sorghum. 2. In the sprouting phase of sorghum. 3. In the phase of 2–3 leaves in sorghum 4. In the phase of 4–5 leaves in sweet sorghum. In the experiment, the corn hybrid Monica 350 MB and the sorghum hybrid Dovista were sown. Rows ratio was 2:2. The first term of sowing was carried out when the average daily temperature of the soil at a depth 10 cm was 10–12 °C, the rest – according to the experimental scheme.

Under the simultaneous sowing of sweet sorghum and corn, the duration of the sowing-sprouting period was 10 days. Under sowing corn in the phase of the sprouting and in the phase of 2–3 leaves of sweet sorghum, the length of the sowing-sprouting period reduced to 9 days. On average, over the years of the research under the simultaneous sowing of corn and sweet sorghum, field germination of corn seeds was 78.3 %, which is 1.5, 2.9 and 5.2 % less compared to the following sowing dates. A high correlation between the temperature of the soil at a depth 10 cm and the field germination of corn seeds (r = 0.95) and the average between amount of precipitation and field germination (r = 0.56) were noted. Duration of the vegetation period of corn in compatible crops with sorghum increases by 1–2 days from the first sowing term to the fourth, and the vegetation period of the sweet sorghum remains practically unchanged (127–128 days). Duration
of the period sprouting-wax ripeness of corn grain in the first sowing period was 115 days, the second and the third –
116 days, the fourth – 117 days. The increase in the length of the vegetation period was mainly observed in the period of 6–7 leaves – the milk ripeness of grain.

Depending on the corn sowing terms in the harvest structure of compatible crops with sweet sorghum, the cobs ranged from 39.2 to 40.4 %, and the sweet sorghum panicles – 16.3–16.7 % from the whole plant. When shifting the corn sowing terms from the first to the fourth, there is a decrease in the proportion of the cobs from 40.4 to 39.2 % and the increase in the stem proportion from 71.9 % to 72.3 %, while the total weight of one corn plant also decreases by 2.3–4.7 %. The proportion of corn leaves, depending on the sowing term, remains practically unchanged – 14.1–14.3 %. In sweet sorghum plants, the fraction of leaves and panicles was practically the same 11.4 % and 16.3–16.7 %, while the mass and proportion of stems increased from the first to the fourth sowing period from 71.9 to 72.3 % and from 518, 4 g to 523.4 g.

On average, over the years of research, the largest yield of green mass in compatible sowings of sweet sorghum and corn was formed in the third-term variant of corn sowing – 79.4 t/ha, the lowest – in the first – 78.4 t/ha. When sowing corn in different terms in the compatible crops with sorghum, there is no significant increase in the yield of green mass. For the simultaneous harvesting of compatible crops of sweet sorghum and corn on silage in the phase of wax ripeness of grain, it is recommended to select the components of the mixture, taking into account maturation groups.

Key words: corn, sweet sorghum, compatible crops, sowing terms, green mass, yield.