PROF MARK HARDY, DR JOHANN STRAUSS AND SAMIE LAUBSCHER, INSTITUTE FOR PLANT PRODUCTION, DEPARTMENT OF AGRICULTURE: WESTERN CAPE
A long-term, large-scale (50 ha) crop and crop pasture rotation trial has been running at the Langgewens Research Farm since 1996. One of the major aims was to determine the effect of selected crop rotation systems on economically sustainable crop and crop/pasture production in the central Swartland.
The identified needs that were addressed in the project, that were relevant to economic evaluation of the rotation systems to be tested, included: increa-
sing crop yields; improving margins in the production system; increasing protein and oilseed production; increasing diversification of the farm for greater financial stability; and reducing input costs.
Outline of trial
Four continuous cropping, four crop/pasture rotation systems are included
in the trial, each in a four year cycle, namely wheat monoculture (WWWW), WWWC, WCWL, WWLC, WMWM, WMCM, WMcWMc-1, and WMcWMc-2 (where W = wheat, C = canola, L = lupin, M = medic and Mc = medic /clover mixed pasture).
All phases of each rotation are present in each year to accommodate the effect of interannual climatic and commodity price fluctuations on crop yields and prices.
A conservation farming approach is applied to the management of all treatments that includes minimum- and no-till land preparation and planting, and retention of crop residues following harvesting (although crop residues are available to the sheep during the dry summer months in those systems that include a pasture phase).
Data from the 2002 to 2010 seasons were included in the gross margin analysis. For each year all direct and in-direct allocatable variable input costs per ha, and gross income per ha (minus marketing costs) for each crop and for the sheep component of each rotation system being tested in the trial, were recorded.
Summary of results
Increasing crop yields
While climatic conditions had an overriding effect on the production of wheat, canola, lupins and annual legume pastures, wheat yields were clearly also significantly affected by crop sequence (Graph 1).
Average wheat yield (per ha wheat) is similar among those systems where 50% or less of the “farm” is planted to wheat, and tends to be greater than in systems where more than 50% of the area is planted to wheat.
Crop sequence did not appear to have a major effect on the yield of lupin, canola and pastures, although canola production in the WWWC and WWLC crop sequences tends to be lower than for the WLWC and MWMC systems.
In the short term, gross margins differed among rotation systems both within and between years. In many instances these differences were, however, not statistically significant. This was, in part, due to large variations in allocatable variable costs, commodity prices and crop yields.
The rotation systems that include pastures provided higher gross margins than the continuous cropping rotation systems (Graph 2). Within the continuous cropping rotation systems the WCWL system provides the highest mean annual gross margin. The mean annual gross margin for the WCWL rotation system is also similar (does not differ significantly) to the mean annual gross margin for three of the rotation systems that include pastures, despite the low and in some years, negative gross margins achieved by the canola and lupin crop sequences.
In almost all years the lowest gross margins were recorded for the WWWW system, while the highest gross margins were recorded for the pasture-
based systems. Rotation systems that included canola and lupins tended to record gross margins that were in the middle of the, within year, range in gross margins over all systems. This trend persisted in the longer term four year “rolling mean” analyses.
One of the most important results from the analyses was that, whilst
the gross margins achieved for canola and lupins was often negative, the inclusion of one or both of these crops into the production system resulted
in improved gross margins when compared to wheat monoculture and tended to increase gross margins of the farming system as the proportion
of wheat in the farming system was decreased.
Negative or near negative gross margins for crops, as were recorded for canola and lupins in this project, often discourage the producer from including the crop into the farming system. But it must be realised that it is the rotation system as a whole that is important and our analyses show clearly that canola should be included in continuous cropping systems despite its often minor direct contribution to cash flow.
Once the farming community has gained the necessary experience on the management requirements for canola (e.g. planting on suitable soils, apply-
ing correct amounts of fertiliser at the correct time, controlling pests and applying correct harvesting methods), this crop will provide an even greater contribution to the total gross margin for the rotation system.
Increasing protein and oil seed production
The results clearly show the major positive effect on the gross margin recorded in those production systems that include alternative crops such
as canola and lupins, relative to the gross margins recorded for wheat monoculture.
Currently, canola and lupins are planted on less than 10% of the total
area planted to cash crops in the Swartland each year. Our results therefore suggest that the area allocated to canola and lupin production should be significantly increased; not only increasing oil and protein seed production
in the Swartland, but also improving gross margins of the production system.
Increasing diversification of the farm for greater financial stability
Reducing the proportion of land planted to wheat and diversifying production systems by including crops such as canola and lupins, and/or annual legume pastures for sheep production, increased gross margins relative to systems with 75% to 100% of the area allocated to wheat production. There was, however, considerable within-rotation system variability in the gross margins recorded among years, due mainly to the effects of climate on crop yields and, to a lesser extent, on “spikes” in input costs as well as commodity prices.
This suggests that while application of a suitable rotation system may assist in improving stability in terms of gross margins recorded on the farm, the gross margins remain relatively unstable (unpredictable) due to factors other than the rotation system applied. However, if financial stability is defined in terms of the probability of achieving, for example, a gross margin in excess of R2 500 per ha in three years out of four, then the rotation systems with 50% or less planted to wheat could be considered more stable than those with a higher proportion of the area planted to wheat.
Reducing input costs
Total allocatable variable input costs of the rotation systems that included sheep production from pastures, were considerably lower than the input costs for continuous cropping systems (Graph 3). In most years the cost of fertiliser (mainly nitrogen) accounted for 35% to 50% of the total input costs associated with the continuous cropping rotation systems.
With the high nitrogen requirements for optimal wheat and canola produc-
tion, and the inherently low organic N availability of continuously cropped Swartland soils, the high N input requirements for wheat and canola in this production region are unlikely to decline. The inclusion of a legume crop such as lupin or annual legume pasture in rotation with wheat and canola, reduces their nitrogen requirement.
Our results are limited to the use of wheat, canola, lupins and annual legume pastures in fixed four year rotation systems. Producers should assess the potential of their land regarding which crops should be planted and in what proportion. The long-term rotation trial at Langgewens provides guidelines and principles that should assist in the planning of economically stable crop and crop/pasture production systems for each farming enterprise.
Results clearly show that the inclusion of annual legume pasture and or alternative crops such as canola and lupins into the wheat production systems commonly practised in the Swartland will, when compared to cropping systems where more than 50% of the farm is planted to wheat:
- improve gross margins on the farm;
- increase wheat production per ha planted to wheat;
- increase oil- and protein seed production;
- in the pasture based systems reduce input costs; and
- have the potential to provide greater financial stability to the farming system as a whole.