WATER USE EFFICIENCY OF IRRIGATED SUGARCANE AS AFFECTED BY ROW SPACING AND VARIETY

Size: px

Start display at page:

Download "WATER USE EFFICIENCY OF IRRIGATED SUGARCANE AS AFFECTED BY ROW SPACING AND VARIETY"

Delphia Carr
5 years ago
Views:

1 WATER USE EFFICIENCY OF IRRIGATED SUGARCANE AS AFFECTED BY ROW SPACING AND VARIETY F OLIVIER and A SINGELS South Afrian Sugar Assoiation Experiment Station, P/Bag X02, Mount Edgeombe, 4300, South Afria Franois_Olivier@sugar.org.za Introdution To meet the hallenge of a limited and ostly water supply, South Afrian sugarane growers will have to find ways of inreasing the effiieny of irrigation to maintain high ane and surose yields. The term water use effiieny (WUE) is generally used as a measure of the overall effetiveness of water (either rainfall or irrigation, or both) for rop prodution. WUE an be defined as ane yield per unit of rop water use (evapotranspiration). water use effiieny (IWUE) is another term ommonly assoiated with WUE, and an be defined as the ane yield response per unit of irrigation water applied. More effiient irrigation systems, aurate irrigation sheduling and agronomi praties suh as mulhing, variety hoie and row spaing are potential means of inreasing water use effiieny. WUE and IWUE values are required for water resoure planning and for the assessment of irrigation management praties. Improved water use effiieny would also redue negative environmental impats by reduing runoff, erosion, drainage and leahing of agriultural hemials. The objetive of this study was to determine the WUE and IWUE of surfae drip irrigated sugarane as influened by the amount of irrigation applied, the variety planted and the row spaing arrangement. The information obtained will be used to develop irrigation reommendations, as well as to test rop models. Preliminary results are reported here. Keywords: sugarane, water use effiieny, variety, row spaing, irrigation, water defiit Methods Experiment 1: Row spaing Variety N25 was planted in dual rows at interrow spaings of 0.4, 0.6 and 0.9 m, with the entres of the dual rows spaed at 1.8 m in all ases. The plant rop was ut bak on 4 April 2002, and the experiment was onduted on the first ratoon. was applied with surfae drip lines plaed at the entre between dual rows, 1.8 m apart. Experiment 2: Variety Varieties N25, N22 and N14 were planted in single rows at 1.5 m spaing, and all three varieties were ut bak on 6 April The experiment was onduted on the first ratoon rop. was applied with surfae drip lines plaed on the row and moved to the entre of the interrow after shoot emergene. Both experiments were onduted on the South Afrian Sugar Assoiation Experiment Station (SASEX) Mpumalanga researh station (25 37 S, E, 187 m), near Komatipoort on a Glenrosa soil form. Standard ultivation, fertiliser and weed ontrol praties were followed. Pro S Afr Sug Tehnol Ass (2003) 7

2 Cane yield was measured at four, six and ten months of age. Four sub-samples of a 0.5 m line of ane were taken at random in eah of three repliate plots. Intereption of photosyntheti ative radiation was measured weekly with an AuPAR linear eptometer (Deagon Devies In, WA, USA). sheduling and water treatments was sheduled using the SQR-Canesim program (Singels et al., 1998) and daily weather data was obtained from an on-site automati weather station. The following irrigation treatments were applied: Full treatment Irrigated to replae 100% of potential evapotranspiration (ETp) Def1 treatment Irrigated to replae 50% of ETp Def2 treatment Irrigated to replae 25% of ETp during the first six months, and thereafter irrigated to replae 50% of ETp. Experiment 1 was subjeted to all the treatments, whereas Experiment 2 was subjeted to treatments Full and Def1 only. In all treatments, 8 mm irrigation was applied when the respetive thresholds were reahed. Treatment Def1 therefore reeived roughly half the number of irrigations reeived by treatment Full. Volumetri soil water ontent (SWC) was measured twie weekly using a neutron water meter, Model 503DR CPN Hydroprobe (Campbell Paifi Nulear, CA, USA). Readings ommened at a depth of 0.25 m, and were taken at 0.15 m intervals thereafter to a maximum soil depth of 1.15 m. Aluminium aess tubes were installed between the dual rows in Experiment 1, and 0.15 m from the single row in Experiment 2. Measured hange in soil water ontent ( SWC), total irrigation (I), total rainfall (R) and total estimated drainage (D) for a given period was used to derive umulative rop water use (CWU) at the end of that period, using the standard water balane equation. Drainage was estimated by the SQR-Canesim model. 250 Cane yield (t/ha) Crop water use SQR-Canesim Defiit irrigation Full irrigation Thompson (1976) Figure 1. The relationship between estimated rop water use and ane yield. Measurements (points) are ompared with SQR-Canesim simulated values and the Thompson (1976) relationship.

3 Results Water status Figure 1 illustrates the relationship between yield and water use. WUE of all defiit treatments were muh higher than the values established by Thompson (1976) and used by the SQR-Canesim model (Singels et al., 1998). A possible reason ould be that the ratio of radiation (whih drives yield) to atmospheri evaporative demand (whih drives evapotranspiration) was higher at the Mpumalanga researh station than the onditions that existed at the experiment sites used by Thompson (1976). The Full treatment had lower WUE values, indiating possible wastage of water. Growers and irrigation planners are interested in IWUE (Table 1) beause it is losely related to irrigation effiieny and profitability. The amount of irrigation had a profound effet on IWUE. For example, IWUE of the 0.6 m row spaing inreased from 13.2 t ane/100 mm irrigation in the Full treatment, to 24.7 t ane/100 mm irrigation in the Def1 treatment (Table 1). This inrease was due mainly to the large redution (50%) in irrigation, while yield delined by only 4%. Field trials at Mount Edgeombe have produed responses that vary from 22 to 48 t ane/100 mm irrigation, depending on the sheduling strategy and rainfall (Inman-Bamber et al., 1998). The inrease in IWUE due to less irrigation ould be asribed in part to redued evaporation from the soil resulting from the lower wetting frequeny of the defiit irrigation treatments. Furthermore, onsiderably more drainage from the root zone was estimated for the Full treatment ompared with Def1 and Def2 treatments. Dual row spaing Spaing of dual rows had no signifiant effet on WUE or IWUE, irrespetive of rop water status (Table1). WUE values for the Full treatment were higher than the 9.7 t ane/100 mm irrigation found by Thompson (1976), but is in agreement with the value of 12.2 t/100 mm reported by Kingston (1994). Treatment Row spaing Full Def1 Def2 Table 1. Yield and water use data for Experiment 1. Yield (t/ha) CWU* ab 1427 a a ab a a b 939 b b b b b d d Rainfall Drainage WUE IWUE 1332 a a 13.5 a 1332 a a 13.2 a 1332 a ab 14.7 a 687 b ab 23.4 b 687 b b 24.7 b 687 b ab 23.0 b 551 b ab 22.8 b 551 b b 25.8 b 551 b b 27.6 b CWU = Crop water use; SQR-Canesim generated CWU values in brakets. ab = Values that have the same subsripts do not differ signifiantly.

4 Variety N14 had higher yield, WUE and IWUE than N22 and N25 (Table 2). Under water stress onditions, N22 had signifiantly lower yield, WUE and IWUE than the other two varieties. The redution in yield as a result of defiit irrigation is a measure of drought suseptibility. Yields of N25 delined by only 3% ompared with 17% for N14 and 30% for N22. These results onfirm the lassifiation of N22 as a drought suseptible variety. Treatment Row spaing Full Def1 Table 2. Yield and water balane data for Experiment 2. Yield (t/ha) CWU* N ab 1447 a 1465 N a ab 1468 N a a N b 939 b 952 N22 99 b 940 N b b Rainfall CWU = Water use; SQR-Canesim generated CWU values in brakets. ab = Values that have the same subsripts do not differ signifiantly. Drainage WUE IWUE 1319 a a 10.3 a 1319 a a 10.6 a 1319 a a 11.4 a 675 b b 19.5 b 675 b a 14.6 a 675 b b 18.6 b General It is interesting that the yield of N25 obtained with dual rows at 1.8 m (Table 1) was 23% higher than that obtained in single rows at 1.5 m (Table 2). The yield response of 58% per 1 m redution in row spaing is muh higher than the value of 13% reported by Boye (1968) and Singels and Smit (2002). WUE and IWUE were therefore also muh higher for dual rows than for single rows. This result an be explained by the inreased intereption of radiation by the dual rows beause of quiker anopy development. Dual rows required 90 days to reah 80% anopy over, whereas the 1.5 m single rows required 120 days. Plant rop results from trials onduted reently in Swaziland ( 1 personal ommuniation) showed that 1.8 m spaed dual rows (0.4 m apart) produed higher yields than the standard 1.5 m single rows. However, these results ould not always be repeated in the ratoon rops. Results from trials onduted in Zimbabwe ( 2 personal ommuniation) were also inonlusive. Another interesting aspet of these experiments was the high ane yields obtained at 10 months on the dual row spaing. Another two months of stalk growth and proper ripening ould, theoretially, have lead to surose yields of more than 28 t/ha. Although this was ahieved on soil that is relatively new to ultivation, it is nevertheless an indiation of the high limati potential of the Mpumalanga area. There is onsiderable sope for ane growers to inrease yields and IWUE through improved agronomi management. 1 DWF Butler, Swaziland Sugar Assoiation Tehnial Servies. 2 NL Leler, South Afrian Sugar Assoiation Experiment Station.

5 Conlusions Key findings from this work were: Under well-watered onditions, N14 had slightly higher WUE and IWUE values than N22 and N25. Yield, WUE and IWUE of N25 was signifiantly higher in dual rows spaed 1.8 m apart than in single rows spaed 1.5 m apart. There appears to be a lear yield advantage to planting ane in dual rows where drip irrigation is pratised. The onfiguration of the dual row spaing does not affet yield or WUE. Inreases in WUE and IWUE an be ahieved by reduing irrigation in drought tolerant varieties without ausing severe yield loss. N22 was onfirmed as being suseptible to drought, whereas N25 appeared to be drought tolerant. The data from these experiments will be further analysed to develop pratial irrigation reommendations. Further investigation into the optimal use of limited irrigation water is required. Effiienies need to be expressed in terms of ERC yield per unit of water use or water applied. The data will also be used to refine and test rop models for use as irrigation management support tools. Aknowledgements The authors would like to thank George Kanniappen, Willard Phiri and other SASEX tehnial staff for their hard work during these experiments. REFERENCES Boye JP (1968). Plant rop results of a row spaing experiment at Pongola. Pro S Afr Sug Tehnol Ass 42: Inman-Bamber NG, Singels A and Muhow RC (1998). A systems approah to benhmarking for sugarane prodution in Australia and South Afria. Pro S Afr Sug Tehnol Ass 72: 3-9. Kingston G (1994). Benhmarking yield of sugarane for estimates of water use. Pro Aust So Sug Cane Tehnol 16: Singels A, Kennedy AJ and Bezuidenhout CN (1998). Irriane: A simple omputerised irrigation sheduling method for sugarane. Pro S Afr Sug Tehnol Ass 72: Singels A and Smit MA (2002). The effet of row spaing on an irrigated plant rop of sugarane variety NCo376. Pro S Afr Sug Tehnol Ass 76: Thompson GD (1976). Water use by sugarane. S Afr Sug J 60: and

Experiment Station. Department of Soil and Crop Sciences

Experiment Station. Department of Soil and Crop Sciences Tehnial Bulletin TB06-03 August 2006 Ag riultural Experiment Station College of Agriultural Sienes Department of Soil and Crop Sienes Western Colorado Researh Center Organi Alternatives for Weed Control