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There are two tillage regimes in the UC Davis Sustainable Agriculture Farming Systems (SAFS) project: Standard Tillage (ST) and Conservation Tillage (CT). The ST plots are farmed in a manner typical for the lower Sacramento Valley for a two-crop rotation of processing tomatoes and field corn. CT reduces the number of field operations as much as possible with the economic objective of reducing costs without compromising yields.
Both tillage regimes have two crops, processing tomatoes and field corn, grown using three farming methods: 1) Conventional (Conv) following standard practices in the Sacramento Valley, 2) Winter Legume Cover Crop (WLCC) using a winter cover crop and judicious use of herbicides, and 3) Organic (Org) using a winter cover crop for both crops and additional compost preceding tomato. The organic system follows the legal requirements of an organic system which precludes the use of synthetic pesticides, herbicides or fertilizer. All three production methods are carried out under both ST and CT regimes resulting in six systems for each crop.
The systems using CT differed from the ST system with respect to ground preparation operations and residue management. The Org and WLCC methods include operations for planting and incorporating cover crops. In addition, Org includes one operation for spreading compost. Conv includes additional herbicide operations, the exact number varying from year to year. In some years the CT WLCC and CT Conv used additional herbicide applications and cultivations. CT Org also used additional cultivations in some years. In other years the hand hoeing for tomato was higher in CT than ST.
Several sustainability indicators utilize resource use as the basis of comparison. In our experiments, resource use differs across farming methods (Conv, Org, and WLCC) and between tillage regimes (ST and CT). In all years for both crops and all farming methods, CT systems used significantly fewer farming operations than ST. The decrease in trips across the field from reduced preplant and postharvest operations was always greater than any increase in weed control operations. This decrease in operations translated into reduced fuel use and tractor labor hours. The differences between tillage systems will be discussed in terms of the number of operations, labor use, equipment hours, and fuel use.
| Table 1. Labor and Fuel Usage for Tomatoes and Corn | ||||||
Standard Tillage |
Conservation Tillage |
|||||
| Resource | Conventional |
Organic |
WLCC |
Conventional |
Organic |
WLCC |
| Tomatoes | ||||||
| Machine labor (Hrs) | 7.5 |
6.9 |
7.2 |
5.4 |
4.8 |
5.0 |
| Non-machine labor (Hrs) | 6.3 |
6.2 |
6.3 |
6.3 |
6.2 |
6.3 |
| Gallons of fuel (Gals) | 62.2 |
56.2 |
58.5 |
43.1 |
38.7 |
39.2 |
| Corn | ||||||
| Machine labor (Hrs) | 4.5 |
4.5 |
4.7 |
2.1 |
2.9 |
2.0 |
| Non-machine labor (Hrs) | 1.2 |
1.1 |
1.2 |
1.2 |
1.1 |
1.2 |
| Gallons of fuel (Gals) | 36.1 |
35.4 |
36.7 |
12.3 |
16.8 |
11.6 |
Tomatoes: Using 2006 as an example, the CT Conv tomatoes had 12 trips across the field and 10 for Org and WLCC compared to 21 for the ST systems. Specifically, preplant tillage operations included in ST but not CT were bed-disked three times and ring-rolled once. In contrast, the CT systems only used one strip till pass for a net savings of three trips across the field for preplant operations. Additional postharvest residue management included finish disk (2x), stubble disk, landplane (2X), and list beds for ST. None of these operations are included in the CT systems. Org and WLCC have additional operations related to cover crops while Conv has additional herbicide operations; the result is about half the number of times across the field for CT compared to ST tillage systems.
These differences translates into a reduction in tractor operator labor of 2.1 – 2.2 hours per acre and a reduction in fuel use of 19.1 – 19.3 gallons per acre from using conservation tillage (Table 1). For a 2,000 acre farm with 1,000 acres in tomatoes, this translates into a reduction of 2,100 hours of labor and 19,100 gallons of fuel. Following the convention that tractor labor hours are 10 percent higher than tractor hours to allow for down time and setup time, this is a reduction in tractor use of 1,909 hours between ST Conv and CT Conv.
At first blush, it seems that a reduction in operations of roughly 50 percent should translate into a 50 percent reduction in costs. However, this is far from the case. For processing tomato, most of the costs are in materials, transplants, fertilizer, water, and herbicides. A reduction in tillage operations only decreases fuel, labor, and equipment use and has little direct impact on materials inputs (with the notable exception of some additional herbicide treatments). Further, cutting the number of ground operations in half does not even cut the fuel use in half due to the disproportionate fuel use for the planting and harvest operations, which are very time consuming compared to tillage operations.
Corn: Again using 2006 as an example, ST corn used 21 trips over the field for Conv and 22 trips for Org and WLCC compared to CT corn used, which averaged 11 passes. This represents over a 50 reduction in the number of operations used to grow corn between the ST and CT systems. Unlike tomato, all of the reduction in operations comes from the difference in residue management. Preplant operations do not vary between tillage regimes, only across farming methods. The operations included in ST but not CT are finish disk (2X), stubble disk (4X), landplane (2X), and list beds. The result is a reduction in tractor operator labor of between 2.4 and 2.7 hours per acre and between 23.8 (Conv) and 25.1 (WLCC) gallons of fuel per acre. For 1,000 acres of conventionally grown corn, this means a reduction of 23,800 gallons of fuel, 2,400 tractor labor hours, and 2,181 tractor hours.