Sugarcane spacing I. Historical and theoretical aspects.

Row spacing has apparently evolved from close to wide spacings as an accommodation to mechanization. A review of experiments in over 80 years showed that decreased spacings resulted in increased yields of cane. More pronounced responses have been reported in temperate and sub-tropical sugarcane areas, but significant yield increases with closer spacings have been reported from the tropics. For a given area, as interplant distance decreases arithmetically, the plant population increases exponentially. Even though plant weight and the number of stalks per plant decrease with decreased spacing, the effect of population is such that the theoretical yield also increases exponentially with closer spacing. DISCUSSION I In established natural stands of wild canes (Saccharum spontaneum), culms of small clones may grow as close as 2 cm and culms of larger clones may be only 5 cm apart. Cultivated sugarcane varies in interrow spacing; rows of S. barberi may be 30 crn apart and rows of the inter-specific hybrids in commercial production vary in distance from 60 to 240 crn (Table 1 ). In the past, interrow distances probably were less than those used at present. Spacings of 60 cm in 1819, 79 cm in 1833 and 91 cm in 1848 were described for Louisiana (Fleishmanm7, Silliman18 and Spaldinglg),; and 91 cm for Spain (Spaldingl 9). In an extensive review of interrow spacing studies before 1930, WebsterZ2 reported that rows in India were as close as 46 cm. while in Argentina and Hawaii, rows were as wide as 244 cm with varieties of S. officinarum. After reviewing 214 comparisons in 6 countries, Webster concluded that, in the majority of cases, greater yields were obtained when cane was planted on close rows, and he cited the conclusion of Cross in 1919 which stated that the distance between rows of sugarcane should be the smallest which permits cultivation with modern equipment. Row spacings from 60 to 90 cm can still be found where sugarcane is produced by man and animal power. Wider spacings 1 are popular where some mechanization has taken place. Among the earliest documented experiments on row spacing were those of W. C. S t ~ b b s ~ O , ~ ~ , who found that decreasing interrow spacing increased yields of S. officinarum. Even though he obtained as much as 23% more cane from 91 cm than from those with 150 cm rows, Stubbs lfreferred the latter because of the economy of seed cane. Spacing experiments have been repeated with different varieties and in different parts of the world. Of the 17 rowspacing experiments in 12 cane-growing regions (Table I), decreased interrow spacing increased yield from 5 to 89% in all but one test, with an overall average increase of 31%. Seven tests have spacings of 61 cm or less, and these included some of the larger increases as well as the only decrease. That none of the comparisons reviewed by W e b ~ t e r ~ ~ , and less than half of the experiments in Table 1 included treatments with row spacings of less than 61 cm is probably due to pragmatic reasons relating to planting and cultivation. TABLE 1. Increased sugarcane yierds through decreased row spacing. Average Average yield change lnterrow wider closer Age a t Location Hawests spacing (cm) spacing spacing hawest Reference no. from to tlha % mo Mississippi, USA 32ON 6 182 91 52 +35 8 ( 3) 3I0N 6 182 91 54 +70 8 ( 3) Georgia, USA 3I0N 3 168 107 . 60 +25 8 ( 8) Louisiana, USA 290N 4 182 61 85 +89 9 (12, 13, & unpubl. data) 7 182 91 82 +31 9 (1 61 Florida, USA 27ON 3 150 50 98 +41 12 (Gascho, unpubl. data) 3 152 91 90 + 5 1 2 1 6 (16) Taiwan 23ON 2 120 60 70 + I 1 8-9 ( 9) 2 120 80 50 +30 ( 5) Hawaii, USA 200N 1 240 150 222 +36 20 ( 6) Puerto Rim, USA 18ON 3 152 91 142 +I7 (Samuels unpubl. data) 6 152 91 127 + I6 (14) Dominican Republic 18ON 3 175 106 90 +48 12-18 (15) Philippines 15ON 1 125 50 148 +63 (17) Rhodesia 22% 2 200 50 134 + 6 12 ( 1) Australia 27OS 2 140 50 80 +48 12 ( 4) South Africa 30°S 2 137 46 144 8 12-20 (21) 2 218 89 109 + I 6 12 ( 2) Sugarcane grown on closely spaced rows i s believed to succeed in high latitudes because of the maximum utilization of both land area and incident light during a growing season shortened by frost. This view is supported by results from frost-prone areas (Georgia, Illississipi, Louisiana, Table 1). Results