Field experiments were conducted on loamy sand at Ludhiana to study the responses of the potato crop to mild stress and severe stress imposed at (I) tuber initiation stage, (II) early tuber enlargement stage and (III) late tuber enlargement stage, individually and repeatedly. Mild stress was created by irrigating the crop at 25–33 mm net cumulative pan evaporation (CPE) and severe stress, at net 39–49 mm CPE.
Severe water stress at stage I alone reduced seed yields by 3.20 and 3.27 t/ha and the number of seed tubers by 6.6 and 10.0/m2 in 1978–79 and 1979–80, respectively; that at stage II depressed ‘ware’ rather than seed and that at stage III kept down ‘ware’ only. The effect of stress at the different stages individually on total yield and N-uptake was almost the same. Plant height was most sensitive to the stress at stage II, followed by that stage I. Repeated severe stress accentuated the deleterious effect on plant growth and yields, though the cumulative effect was lower than the sum total of the effects of single-stage stresses individually. The response to mild stress, though subdued, pointed in the same direction as that to severe stress.
In 1979–80, total yield fell from 14.1 to 7.5 t/ha with decrease in mean relative leaf water content (RLWC) from 87.5% under no stress to 75.7% repeated stress. The rate of fall in yield per unit decrease in relative leaf water content was steeper under single-stage stress treatments.
