324 PEAR GROWING IN CALIFORNIA. 



pear districts is vetch. The two species commonly used are hairy 

 vetch (yicia villosa) and purple vetch- (Vicia atropurpurea ) . This 

 plant thrives well 'under the climatic conditions of the average winter 

 and makes a splendid growth to plow under in the spring. See Fig. 129. 

 It is sown in the fall, preferably before the rainy season begins, and 

 grows throughout the winter. Plowing may be done any time in the 

 early spring when the growth of the plant has become satisfactory. 



If cover crops are desired during the summer season their use 

 will depend principally upon the availability of a sufficient supply 

 of water for irrigation. Clovers, vetches, beans and peas of any kind 

 that will do well under the existing conditions may be used. Alfalfa is 

 frequently sowed as a cover crop. Where the supply of irrigation 

 water is great enough to insure against either the trees or the alfalfa 

 becoming too dry there is no better cover crop when not grown too 

 long. Alfalfa being a perennial plant, there is always a tendency 

 to leave it in the orchard too long after planting, cutting it several 

 times each season for hay, to the possible detriment of the trees. There 

 have been some exceptions to this rule and there are orchardists who 

 favor the growing of alfalfa in an orchard year after year. The 

 extremely deep rooting of this plant makes it valuable in improving 

 the physical condition of the soil and bringing up the plant food 

 from a greater depth than the ordinary cover crop root systems reach. 

 Alfalfa allowed to grow in a pear orchard for one season only, if 

 plowed under when there is a maximum amount of green material, 

 is an exceedingly valuable cover crop. If it grows longer than one 

 season plowing is difficult because of the very tough roots and the 

 trees may not do as well because of its presence. When used as a 

 cover crop alfalfa should be drilled between the tree rows, being kept 

 at a distance of at least 3 feet away from the trees. With ordinary 

 precautions where there is plenty of water the use of alfalfa is rec- 

 ommended. Where water is scarce it should never be grown as it 

 requires a large amount of moisture and frequently trees are stunted 

 because of its use as a cover crop under drought conditions. 



FERTILIZERS. 



Under the previous heading the fertilizing value of cover crops, 

 especially the legumes, was briefly discussed. The judicious use of 

 such crops where conditions will permit of their growth will result in 

 good tree growth, and the production of big crops of good fruit with- 

 out the addition of other fertilizers. It must be remembered, how- 

 ever, that nitrogen is the only essential element of plant food that is 

 added to the soil by plants of the family Leguminosae. Indirectly 

 they serve another valuable purpose in that they greatly improve 

 the physical condition of the soil and render more available potash 

 and phosphoric acid, which are the other two elements of plant growth 

 that are essential in every soil. 



BARNYARD MANURE. 



The addition of nitrogen may be accomplished through the use of 

 barnyard manure, as well as the growth of leguminous cover crops. In 

 fact, experiments that have been directed by our state experiment 



