IRRIGATION AND CULTIVATION 267 



according to season and soil, a thorough cross-harrowing should 

 leave the field in good shape. On light soils disposed to be dry, a 

 light rolling may be beneficial. As soon as the plants appear, har- 

 rowing with the rows mellows the surface, kills small weeds, and 

 does not hurt the potatoes. Cultivation between the rows should 

 soon follow and the surface should be kept loose until the plants 

 are quite high. Good, clean culture is the rule with potatoes. In 

 some soils, not disposed to dry out too rapidly nor to crust, crops 

 are often made with little cultivation after weeds stop growing, 

 especially where the plant has the benefit of coast influences, but 

 cultivation for moisture retention, where needed, must be more 

 thorough. 



On lands subject to excess of moisture, winter growth of po- 

 tatoes can be facilitated by the ridge planting described in Chapter 

 VII; but where this is not likely to occur, flat culture is best, both 

 in winter and summer. Where potatoes are to be irrigated a slight 

 moving of the soil toward the row, so as to make the interspace a 

 little hollow to carry water, is admissible, but "hilling up" is un- 

 necessary and dangerous. It usually uncovers the firm soil and 

 exposes the roots to too great heat and drought. It is also likely 

 to bring the tubers within reach of the moth from whose eggs come 

 the potato worms. During the latter part of the growth the tuber 

 should be well covered with soil. 



Irrigation. The potato should be kept growing thriftily from 

 start to finish. If growth is arrested by drought, a new growth of 

 small potatoes is apt to start upon renewal of moisture, to the detri- 

 ment of the crop. The aim should be, then, to keep the soil ade- 

 quately moist until maturity approaches. This is best done by run- 

 ning small streams between the rows, the planting having been ar- 

 ranged for this distribution. As already stated, excessive irriga- 

 tion is decidedly detrimental to the quality of the crop, and extra 

 effort must be made for even distribution of the water. To allow 

 low places to fill up with water is injurious and to allow the water 

 to come in contact with the plant stems is also dangerous. A good, 

 thorough and uniform wetting of the soil is often enough to finish 

 the crop and it is seldom desirable to irrigate after the bloom ap- 

 pears. Thorough surface cultivation should follow the irrigation, 

 for the reasons stated in the chapter on that subject. 



In connection with the irrigation of potatoes it must be borne 

 in mind that many troubles may arise from irregularity in the moist- 



