The paper presents a model to calculate the costs for weed control in organic row crops. The model makes it possible to analyse the economic consequences of different weed control strategies in row crops. Particularly the time needed for hand-weeding had a strong impact on the costs

Melander, Senior scientist Bo

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  1   Economic Aspects of Physical Intra-Row  Weed Control in Seeded Onions  Bo Melander1    Hand weeding is still widely used in Northern Europe as the primary method for controlling weeds growing between the crop plants in the row (intra-row) in organic vegetables, such as seeded onions and leek, and carrots. Weeds between the crop rows (inter-row) can normally be controlled satisfactorily by inter-row cultivations.    Danish and Swedish vegetable growers commonly spend 100-300 h ha-1 to hand-weed onions and carrots (Ascard, 1990; Nielsen and Larsen, 1991), but the time may reach 500 h ha-1 in particularly weedy situations (Melander, un-published). This is an appreciable financial burden in organic vegetable growing. Therefore, research has been conducted in recent years looking for effective physical intra-row weed control methods. New results have shown that combining pre-emergence flaming with post-emergence brush weeding can control more than 80% of intra-row weeds in seeded onions and kale without significantly damaging the crop (Melander, 1998). However, such a strategy is based on the use of special and expensive machinery. To the grower, this means considerable machinery investments.    The objective of this paper is to compare the economics of physical intra-row weeding and pure hand-weeding, exemplified respectively by two weed manage-ment systems for seeded onions grown in single rows with 50 cm row spacing.    Materials and Methods  Weed management systems considered   In the first system (S1), intra-row weed control uses only hand weeding, while inter-row weeding is based on conventional hoeing with no extra need for manual weed removal.  __________________________________________________________________ 1Danish Institute of Agricultural Sciences, Department of Crop Protection, Re-search Centre Flakkebjerg, DK-4200 Slagelse, Denmark; Bo.Melander@agrsci.dk    2   In the second system (S2), pre-emergence flaming and post-emergence brush weeding are used to control intra-row weeds, while hand weeding is used to control weeds that survive the physical methods. As in S1, inter-row weeds are controlled by conventional hoeing but with fewer passes, because the physical intra-row methods also control inter-row weeds. Brush weeding is done with a three-row vertical-axis rotary brush weeder. This implement is described in detail in Melander (1997). Results and experience obtained from former and current field experiments (Melander, 1998, and unpublished data) have shown that a strategy starting with pre-emergence flaming followed by two brush weedings may give 80-90% intra-row weed control. The first pass with the brush weeder is done when the onions are 5-8 cm tall, the second when they are approximately 10 cm tall. The adjustments of the brush weeder appropriate for seeded onions at the two treatment times are described in detail in Melander (1998). Re-emerging weeds and weeds surviving the physical methods have to be removed manually.  Equations used for the economic analysis   The annual costs TC ($ ha-1) for each system, S1 and S2, were calculated from the following basic equation: TC  = E1 + E2 + …….. EN + HW   (1) where E is cost for weeding with implement 1, 2 and up to number N, respec-tively, and HW is the cost for hand weeding of weeds surviving physical weed control. E was calculated as:  E  =  OE + PN(VC + MC + TE)   (2) where OE is overhead expense, PN is number of passes, VC is the variable cost, MC is the cost for manual operation of the implement, and TE is the tractor cost. VC includes the costs of repairs, maintenance, and gas consumption when flaming. OE was calculated according to a commonly used annuity formula: OE = [IC(r/(1-(1+r) -RP))]/A   (3)   where IC ($) is the initial cost for the implement, r (%) is the interest rate, A (ha) is the area to be treated annually, and RP is the repayment period in years. TE was calculated as: TE = (TH + TW)/WC    ( 4 )    3where TH ($ h-1) is cost per tractor working hour (which includes expenses for investment, repairs, maintenance, insurance, and fuel consumption), TW ($ h-1) is the labour wage, and WC (ha h-1) is the working capacity of the implement (including 20% time for turnings). MC was calculated as: MC = NPTW /WC    ( 5 )  where NP is the number of persons needed to operate the implement. The cost of hand weeding was calculated as: Hw = [a + bWD(1- WE)] TW   (6) where a and b are parameters from linear regression between time consumption for hand weeding and increasing weed density WD (plant/m-2), and WE is the overall percentage weed control effect of the physical methods used in system S2. (WE is 0 in system S1.) Parameter a (h ha-1) reflects the time it takes to move along the rows looking for weeds, and b (h m2 plant-1 ha-1) is the time for hand weeding per unit plant density. Further details about the economic aspects of mechanical weeding can be found in Weber (1997).  Parameter values   The parameter values presented in Table 1 were all fixed values in the calcu-lations. All prices are Danish levels, but the currency is the US dollar ($). The parameter values were obtained from: field experiments conducted previously (Melander, 1997, 1998); ongoing field experiments (Melander, unpublished); the Ph.D. dissertation of Weber (1997); and information from the Danish Machine Pool Organisation and the Danish Agricultural Advisory Centre. Parameter values for A, WD, WE, and TW were all varied as shown in Figure 1. (TW =15 $ h-1 corre-sponds to the Danish minimum wage for adult labour).  Results and Discussion   The size of the area treated annually has a strong influence on the economics of using physical intra-row weeding as shown in Figure 1. The cost-savings when using system S2 compared with system S1 are either small or even negative when only small areas are grown. This is because the high investment in machinery is only used on a small area. However, a high weed density changes the economics strongly, as system S2 becomes economically beneficial even on smaller areas. The cost for hand weeding is the major reason, because high weed numbers require many hours of hand weeding, which overshadows the cost for machinery investment and use.    4Table 1. Fixed parameter values used in the economic analysis (equations 1-6). All prices are Danish levels.  Weed System Method PN  NP W C (ha/h)  IC       ($) RP(y) r (%) VC ($/ha) TH ($/h)  a (h/ha) b       (h m2    pl-1 ha-1)  S1  hoe 4  0  1.20  5,199  10  8  2.1  9.2  -  -   hand   -  -  -  -  -  -  -  -  28.2  0.93 S2  flame 1  0  1.44  15,150  10  8  note  2  9.2 -  -  brush    2  1  0.24  8,778  10  8  11.6  9.2  -  -  hoe  2  0  1.20  5,199  10  8  2.1  9.2  -  -  hand    -  -  -  -  -  -  -  -  28.2  0.93  2VC was calculated as: VC = (527/A) + 46, where $527 is the annual fixed cost for required overhauling and repairs and $46 is the cost of gas per ha (gas consumption is 50 kg ha-1).    Less successful physical weeding resulting in lower weed control effects than the optimal 80% will generally reduce the benefits of system S2. This is particularly evident at the low wage level and low weed density. At the low wage level, the benefits of system S2 are present only for larger treated areas with high weed infestations. For countries with wage levels much lower than those pre-sented here, it is questionable whether larger machine investments for weed con-trol in vegetables could be profitable at all.   The present analysis does not account for other aspects, such as the release of time and manpower that the mechanisation of intra-row weed control would cause. In many parts of Northern Europe, where it might be difficult to find enough labour for hand weeding, physical intra-row weed control could increase the possibilities for growing more profitable organic vegetables and thereby improving income.  Conclusions   Physical intra-row weed control methods, such as flaming and vertical brush weeding, can reduce considerably the time required for hand weeding in seeded onions. The economic benefits of these techniques compared with pure hand weeding are very great in situations where: labour wages are high (North Euro-pean level), the annual area grown with onions is relatively large, and the weed infestation level is high. In contrast, the methods become uneconomical when   5wages and the area treated annually are low, unless the weed density is extremely high or the machinery costs can be lowered considerably.      Figure 1. Graphic presentation of the cost savings when using weed management system S2 compared with pure hand weeding S1 for weed control in seeded on-ions. The analysis was done according to equations 1-6. WE is the percentage effectiveness of physical intra-row weeding. The dotted and full-drawn lines are high (500 plants m-2) and low (100 plants m-2) weed densities, respectively.     References  Ascard, J. 1990. Weed control in ecological vegetable farming. In A. Granstedt (ed). Proceedings of the Ecological Agriculture, Nordiske Jordbrugsforskeres Forening, Seminar, 166, 178-184. -4000-3000-2000-100001000200030004000500060000 2 4 6 8 10 12 14 16 18 20-4000-3000-2000-100001000200030004000500060000 2 4 6 8 10 12 14 16 18 20-4000-3000-2000-1000010002000300040005000600002468 1 0 1 2 1 4 1 6 1 8 2 0-4000-3000-2000-100001000200030004000500060000 2 4 6 8 10 12 14 16 18 20Cost-savings ($ ha-1) Time wage TW = 7.5 $ h-1  Time wage TW = 15 $ h-1  WE = 80% WE = 80% WE = 50% WE = 50% Treated area A (ha)   6Melander, B. 1997. Optimization of the adjustment of a vertical axis rotary brush weeder for intra-row weed control in row crops. Journal of Agricultural Engeneering Research 68: 39-50. Melander, B. 1998. Interactions between soil cultivation in darkness, flaming, and brush weeding when used for in-row weed control in vegetables. Biological Agriculture and Horticulture 16(1):1-14. Nielsen,V., and Larsen, E.K. 1991. Mekanisk ukrudtsbekæmpelse i økologisk jordbrug. I. Litteraturstudier. Kortlægning. Foreløbige resultater. Statens Jordbrugstekniske for-søg, Danmark. Orientering, 73.  Weber, H. 1997. Geräte- und verfahrentechnische Optimierung der mechanischen Unkrautregulierung in Beetkulturen. Dissertation, Institut für Landtechnik der Tech-nischen Universität München, Germany.  

Economic Aspects of Physical Intra-Row Weed Control in Seeded Onions

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