Conservation Agriculture Research and Evaluation Programme 2012-2015, Zambia (CAREP): Final Report

Prosjekt avsluttet

The main purpose of promoting conservation agriculture in Zamiba is to enhance soil fertility and hence improve food security, poverty alleviation and environmental sustainability. This study determines the extent to which farmers benefit from conversion to conservation agriculture.

Resultater / funn

Trained and dedicated ‘adopters’ of conservation agriculture do not practice ‘conservation agriculture’ as the term is normally understood. Commonly, they practice only reduced tillage combined with the use of herbicides. Since most of them do not leave more plant residues in the field than conventional farmers or use nitrogen-fixing cover crops or fallow crops, soil fertility is not improved by ‘conservation farmers’.

Farmers who practice reduced tillage and chemical weed control, commonly referred to as ‘adopters of conservation agriculture’, do not generally obtain higher yields than those practicing conventional agriculture when both cropping methods are implemented with similar inputs and agronomic skills. In cases where they do get higher yields, the difference appears to be primarily due to higher inputs of fertilizer. In years with poor rain and generally low yields, higher investments in herbicides by conservation farmers may not pay off. The farmers may experience lower profit or even net losses. Total labour is about the same for conservation and conventional tillage.

Fertilizer efficiency decreases with increasing rate of application, particularly in reduced tillage. This may be a result of loss of nitrogen when rip lines and basins are flooded. Loss of nitrogen during heavy rainfall early in the season and ‘salt burning’ of seeds during drought periods might be reasons for low fertilizer use efficiency when the fertilizer is applied to small soil volumes around the seed or plant.

Best yields appear to be achieved when planting is done at a time when the soil is properly moist for even germination and deep root development. Planting at the time of the first few showers of the rainy season seems to have resulted in below average harvest. The correlation between yield and planting date is, however, weak. Some farmers appear to be overly focused on ‘early planting’ as a result of conservation training.

Conservation tillage is associated with early planting, and early planting is associated with a higher fre­quency of replanting and re-application of fertilizer. Spots in fields with poor growth were most commonly caused by soil infertility, poor germination, uneven fertilizer application and water logging. No cases of spots with poor growth were found to be due to a plough pan.

Conservation and conventional farmers interpreted the results from the agro-economic study in similar ways. Both groups concluded that lack of inputs and erratic rainfall are the main challenges for farmers. Tillage methods are of minor importance for crop yield. However, conservation agriculture is generally more cost and labour intensive, while conventional agriculture can be practiced on a lower budget and thereby potentially deliver higher profit. Farmers expressed hope that something more substantial could be done to help them rather than continuing the teachings that have failed to bring about changes in their lives. They asked for help in terms of water for irrigation during dry spells and inputs that would help them make full use of their land. Some of them indicated that there is a need to focus more on the organic aspects of conservation farming and reduce the reliance on chemical weed control. The farmers involved in workshops expressed a desire to be trained in farm management for best profit, not just for higher yields.

No cultivation-induced hardpans (plough/hoe pans) capable of restricting root growth exist in the stud­ied soils. Soils under conservation tillage were more compact at five centimeters depth than soils under conventional tillage. Surface crusts appear to be more common in soils under conservation tillage than conventional tillage. There is no reason for extension agencies to continue advising farmers in the study areas to rip or dig planting basins in order to “break the hardpan”. Deformation of taproots in soils under unmechanized tillage, as reported in the literature, is more likely caused by temporarily dry subsoil early in the rain season rather than by permanent plough pans.

The study does not support the general notion that conservation tillage – as practiced by lead farmers – is more “climate smart” than conventional tillage in terms of soil water. The inconsistency between results from earlier studies under controlled conditions and the current results is presumably due to lack of soil cover and due to the development of surface crusts in the fields of this study. Full tillage loosens the soil across the entire field and thereby allows more water to infiltrate. However, in years with low rainfall, the concentrated water infiltration in rip lines and basins may be beneficial for plant growth.

Ten to fifteen years after planting, Faidherbia albida trees in farmers’ fields have no beneficial effect on yield. The supply of nitrogen in litterfall is high, but nevertheless, the improvement of soil fertility is marginal. The contribution of nitrogen in manure under trees in regions with substantial cattle and sheep herds is relatively small – in the order of one to three percent of the contribution from litterfall from large trees. The apparent discrepancy between measured supply of plant nutrients in litter from Faidherbia albida trees on one hand and soil chemical parameters and crop growth on the other hand, might be explained by rapid carbon and nitrogen depletion by termites.

Farmers practicing conservation tillage start their harvest of green maize on average nine days earlier than those practicing conventional tillage. Farmers use several tillage methods over the annual cycles. Choice of tillage practices is influenced by a range of factors, such as availability of labour, equipment, and money, as well as weeds, soil type, crop, tradition, and weather conditions.

Weeding by hand hoe is generally most common in the studied areas. Use of hand hoe is cheap and effective, but it is also slow and strenuous. Hand hoeing is mostly used for smaller areas. Weeding with oxen ranks second in popularity. It is a fast, cheap and easy method, but expensive or unavailable for farmers without oxen. Herbicide is the least common method. Farmers reported that the method is cheap and fast, but many farmers lack the necessary equipment and knowledge. Safety measures are generally not implemented, and containers are not disposed of properly. Many farmers have to weed with hand hoe after initial herbicide application due to ineffectiveness or lack of funds to buy more herbicide. Women do more hand hoeing than men, while men do mostly all weeding with oxen. Conse­quently, men weed larger areas than women. Herbicides are used slightly more by men than by women.

Farmers have multiple sources of food. Among the studied farmers who practice both conservation farming and conventional farming, the contributions of the farming systems towards consumed food are quite different. The contribution towards food consumed for breakfast was higher from conventional farming than from conservation farming. This is because of crops, such as sweet potatoes, are almost exclusively grown under conventional faming. Contributions from conservation farming towards lunch and supper were higher than from conventional farming. This was because the studied farmers were prioritizing conservation fields over conventional fields in terms of inputs. Thus the production especially of maize from the conservation fields was higher than from conventional farming.

Hand hoe-based tillage methods are in women’s domain while animal-based and tractor-based tillage are in the men’s domain. Joint domain is more prominent in manual tillage than in tractor-based tillage. The change from hand hoe, through animal, to tractor tillage shifts labour from women to men.

Generally, the involvement of both men and women is more prominent in conservation farming with basins than in hand hoe-based conventional farming. However, the involvement of women is still gener­ally higher in conservation farming basins than in hand hoe ridging. This shows that more men from households doing conservation basins tend to work together with their wives than men from house­holds practicing hand hoe ridging. Men are also more involved with their spouses during dry season till­age than during wet season. Men’s domain in ox draught conservation farming is more pronounced than in ox draught conventional farming. This is because of higher level of working together of men and women in conventional farming than in conservation farming. These results show that a shift from conventional farming to conservation farming reduces the involvement of women’s labour.

On-station trials verified that early planting with maize, velvet beans and maize/cowpea monocropping have shown their superiority with regard to maize yield performance and hence, are suitable for recommendation to smallholder farmers. Early planting gave higher yields if applied fertilizer is not leached out of the soil before the crop can take up the nutrients. Best fertilizer effects appear to be obtained when applied one to two weeks after planting.

Maize yields in monocropping showed a reasonable response curve to fertilizer at Chisamba, where 200 kilogram per hectare might be an optimum fertilizer rate. The response at Magoye seems to indicate a lower optimum, around 100-150 kilogram per hectare. Good soils give higher return from investments in fertilizer.

Intercropping with cowpeas did not improve yields during the two seasons. On the contrary, in two of three seasons, monocropping did better than intercropping.

Hoe cultivation, ox ploughing and basins gave relatively high yields in this experiment and better than ripping and zero tillage. Variations between seasons are large, indicating that other factors than tillage are important for crop performance. The trial did not run long enough to show potential differences in soil bulk density and organic matter as a function of soil tillage.

On-station data show no conistent effect of basin size or ripping depth on yield. Thus, the less labour and energy demanding methods appear to be more favourable for farmers than the more labour intensive methods.

Yields were similar for the different weeding methods with a possible, small yield increase for the fully chemical method. If farmers have to pay hired labourers to do the weeding, the chemical/biological and the chemical methods stand out as the most economical methods for farmers, superior to the two mechanical methods in terms of total cost. If farmers can do the weeding themselves, then the expenses will be lowest for manual weeding.

Maize grown under seven to nine years old Faidherbia albida trees on the research station at Chisamba without additional supply of plant nutrients resulted in complete crop failure. With a fertilizer application rate of 100 kilogram per hectare Compound D and 100 kilogram per hectare urea, maize under F. albida gave 1/3 of the yield obtained without trees. Sorghum productivity appeared negatively affected by F. albida trees, probably due to shading. Visual inspections in the field support the conclusion that maize and sorghum plants under F. albida trees were not positively affected by the trees. Seven to nine-year old F. albida trees planted in a 10 x 10 meters grid do not have any positive effects on yields in a farming system with crop rotation.


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