Attractiveness of corn causes it to be grown all over the Poland’s territory, even in regions with the least advantageous climates. In order to asses the risking in marginal settings it was assessed the influence of temperatures and rainfall on the developmental pattern, degree of maturity reached, and total yield of corn (variety of FAO number - 270). Data were collected on the base of 15-years field experiment. Whole vegetative period was described by assigning commencement time (relative to sowing - F0) of each stage to corresponding variables: emergence (F1), rowing (F2), tasseling (F3), cobing (F4), blooming (F5), milk maturity (F6). In addition there were observed one more variable: date of harvest (F7) since due to the region’s climate it does not perfectly match the timing of full maturity stage. It was performed stepwise multiple analysis of regression with selection of optimal subset. Average temperatures(t) and total rainfalls(r) were collected for the following intervals:
two weeks before sowing (t,r1),
sowing - sprouting, emergence (t,r2),
emergence – rowing (t,r3,
rowing - tasseling,(t,r4),
tasseling – cobing (t,r5),
cobing – blooming (t,r6),
blooming – milk maturity (t,r7),
milk maturity – harvest (t,r8).
The full matrix included 112 parameterized variables. Selected results are summarized below.
The following are multiple regression equations estimating time (in days) of commencement of each developmental stage (relative to sowing - F0) depending on selected factors:
(F1) = 17.49 + 0.55r1,
(F2) = 37.70 + 0.68t2-0.65t3 + 0.54r2,
F3) = 127.41 + 0.54t2 - 0.77t3 - 0.43t4 - 0.50r4
(F4) = 91.08 - 0.28t2 + 0.47r1, (F5)=18.77 + 0.67r2, (F6) = 252.23 - 0.73t3 (F7) = 258.53 - 0.37t1 - 0.80t3 - 0.14t5 - 0.40r1 + 0.22r4 + 0.47r5
The estimates of intervals in days between the commencement of each developmental stage were as follows:
(F0-F1) = 32.67 – 0.51t1 + 0.54r1, (F1-F2)=-38.61 + 0.86r2,
(F2-F3) = 25.02 + 0.26t1 - 0.54t4 - 0.24r1 - 0.73r2 + 0.95r3
(F3-F4) = 22.75 - 0.39t1 - 0.36t2 - 0.45t5 - 0.15r1 + 0.74r4 + 0.22r5,
(F4-F5) = 18.78 + 0.67r2
(F5-F6) = 54.94 - 0.65t4 - 0.49t5 + 0.41r3
Total yield and yield quality were estimated as follows:
Y (total yield of green matter) = 84.89 - 0.72t2 -0.04t3+0.55t5-0.63t7 + 0.46t8+0.47r3-0.15r5+0.26r7
Y (yield of green matter of cobs) = 21.16+0.70t1-0.82t2-0.34t3+0.52t5 + 0.01r2+0.42r3-0.28r7-0.06r8
Y (percentage of dry matter in cobs) = -76.67 + 0.19t2 - 0.38t5-0.82t6+0.41r1-0.64r3+0.98r6-0.16r7
Y (total yield of dry matter)= -10.25 + 0.21t5 + 0.44t6-0.35t7-1.5r2+1.90r6+0.03r7+0.55r8
Y (percentage of cobs in full maturity stage) = -227.97 - 0.37t1+0.28t2-0.40t4+1.25t5+0.49r5-0.84r8
Y (percentage of cobs in milk-wax maturity stage)= -77.82+0.28t1-0.21t2-1.60t4+2.62t7+0.46r1+0.38r3+1.06r7
It was concluded on the base of this experiment that corn in extreme conditions displays large variance in yield, ranging from 25.7 to 57.8 dt/ha in total yield and 8.9 to 16.8 t/ha in dry mass. This variance is largely dependent on climatic factors, especially on temperatures during early and late growth stages, and the amount of rainfall mostly in the second half of vegetation period.