The Managing Of Planting Date And Plant Density For Mechanical Harvesting Of Cotton In The Yellow River Valley Of China

Traditional cotton production in China is labor-intensive and time-consuming. Because of socioeconomic development in China, the labor shortages and the rising labor cost have recently become serious and led to a rapid and extensive decrease in the area planted to cotton, especially in the Yellow River valley region. The harvest is the most labor-consuming procedure of cotton production, so it is necessary to develop mechanical cotton harvesting in this region. Thus field experiments were conducted in 2012-2014 to determine the appropriate planting date and plant density suitable for mechanical cotton harvesting in the Yellow River valley according to plant habit, yield, earliness and fiber properties. The main results are as follows:With the delay of sowing date, plant height, main stem diameter and the length of fruiting branch were not significantly affected, while the node of first fruiting branch and the height of first fruiting branch enhanced. Seed cotton yield was not significantly affected by planting date, however, more bolls and yield were produced by the lower and middle branches in the late planted cotton. In addition, fiber quality was enhanced in late-planted cotton for longer fiber length and stronger fiber strength. Compared with the normal planted cotton, late planted cotton produced less rotten bolls. P2 （in late April or early May, about 10 d later than P1） produced the plant habit of 74.3 to 111.8 cm plant height, 26.9 to 31.5 cm height of the first fruiting branch and 12.2 to 27.0 cm length of fruiting branches, which basically meeting the requirements of mechanical harvested cotton （the plant habit of mechanical harvested cotton is short and compact, with the plant height of 80 to 120 cm, height of the first fruiting branch of above 20 cm and fruit length of no more than 25 cm）. P2 produced the most cotton yield with less rotten bolls and had a similar percentage of open bolls in late September to that of PI, indicating a low risk of late maturity. The fiber length and fiber strength were above or nearly reached 30, which is suitable for mechanical harvesting （the fiber length and fiber strength for mechanica harvesting of cotton was 30 mm and 30 cN/tex, respectively）. When delaying the sowing date to P3 （18～20 days later than the normal planting date）, the plant height was 77.1 to 109.0 cm, the height of the first fruiting branch was 33.0～33.8 cm and the length of fruiting branch was 11.3～26.8 cm, making it suitable for the mechanical harvesting. The seed cotton yield of P3 was 9.6%～13.8% less than P2 but nearly equivalent with PI in dry year. Otherwise, the significantly decreased open boll percentage in late September of P3 indicated a delayed earliness and caused a 9.2% yield loss compared with PI in wet year. However. P3 produced the best fibers with fiber length and fiber strength both above 30. Considering the requirements for plant habit, yield, early maturity, and fiber quality for mechanical harvesting of cotton, the appropriate planting date in the Yellow River valley was P2.With the increase of the plant density, plant height reduced significantly, while the height of the first fruiting branch increased obviously, and the length of sympodium shortened significantly. Plant density had little effects on cotton yield, but distribution ratio on inner fruiting branch site increased evidently when increased the population density. In wet year, fiber length of the middle and upper bolls increased and thus improved fiber quality. When increasing the density from 67,500 plants hm^-2 （D1） to 90,000 plants hm"2 （D2）, the plant height was 75.9 to 110.6 cm, the height of first fruiting branch was 28.8 to 30.0 cm and the length of fruiting branch was 17.3 to 21.4 cm, which was 2.7 to 3.2 cm shorter,1.2 to 2.5 cm higher and 0.5 to 5.0 cm less than that of PI and more suitable for mechanical harvesting. D2 produced 2.4～2.6% less yield than D1. But it had the compatible fiber quality to P1 with fiber length that greater than 30mm and fiber strength reached 30 cN/tex. The earliness of D2 was not delayed since the open boll percentage in late September was as high as D1. Compared with D1, D3 (120,000 plants hm^-2) showed a 6.9～7.1 cm shorter plant height,1.7～8.3 cm shorter fruiting branch length and 3.0-3.8 cm higher height of the first fruiting branch, which was more suitable for mechanical harvesting. In dry year like 2013, D3 had a slight yield increase, but in wet year like 2014, the yield was 11% less than D1 and the earliness was significantly delayed. The value of micronaire of D3 was lower than D1,and fiber length and fiber strength were above 30, indicating enhanced fiber quality than D1. Considering the requirements for plant habit, yield, early maturity, and fiber quality for mechanical harvesting of cotton, the appropriate plant density in the Yellow River valley was D2.Therefore, according to requirements for plant habit, yield, early maturity, and fiber quality for mechanical harvesting of cotton, the appropriate planting date in the Yellow River valley was determined to be the end of April or beginning of May （P2）. The appropriate plant density for mechanical harvesting should be about 90,000 plants hm^-2 （D2）.