Talking soil science with farmers

When agricultural researchers visit farms in order to gather information for their research programmes, farmers rarely get proper feedback. Research information on scientific concepts such as soil fertility and nutrient balances is often considered too abstract for them. Researchers in Kenya returned to farmers to discuss their results in the context of Farmer Field Schools. Through the workshops that ensued, they managed to find a common language to bridge the communication gap

Carbon and nutrient losses during manure storage under traditional and improved practices in smallholder crop-livestock systems - evidence from Kenya

In the absence of mineral fertiliser, animal manure may be the only nutrient resource available to smallholder farmers in Africa, and manure is often the main input of C to the soil when crop residues are removed from the fields. Assessments of C and nutrient balances and cycling within agroecosystems or of greenhouse gas emissions often assume average C and nutrient mass fractions in manure, disregarding the impact that manure storage may have on C and nutrient losses from the system. To quantify such losses, in order to refine our models of C and nutrient cycling in smallholder (crop-livestock) farming systems, an experiment was conducted reproducing farmers’ practices: heaps vs. pits of a mix of cattle manure and maize stover (2:3 v/v) stored in the open air during 6 months. Heaps stored under a simple roof were also evaluated as an affordable improvement of the storage conditions. The results were used to derive empirical models and graphs for the estimation of C and nutrient losses. Heaps and pits were turned every month, weighed, and sampled to determine organic matter, total and mineral N, P and K mass fractions. Soils beneath heaps/pits were sampled to measure mineral N to a depth of 1 m, and leaching tube tests in the laboratory were used to estimate P leaching from manure. After 6 months, ca. 70% remained of the initial dry mass of manure stored in pits, but only half of or less of the manure stored in heaps. The stored manure lost 45% of its C in the open air and 69% under roof. The efficiencies of nutrient retention during storage varied between 24–38% for total N, 34–38% for P and 18–34% for K, with the heaps under a roof having greater efficiencies of retention of N and K. Laboratory tests indicated that up to 25% of the P contained in fresh manure could be lost by leaching. Results suggest that reducing the period of storage by, for example, more frequent application and incorporation of manure into the soil may have a larger impact on retaining C and nutrient within the farm system than improving storage condition

Farming systems ecology : towards ecological intensification of world agriculture

The model of intensification that is deeply rooted in the mind of scientists from the green revolution generation is obsolete. We need to think outside the box. Agriculture needs knowledge-intensive management systems to improve food security and incomes in the South, and to reduce the dependence on external (fossil fuel) inputs in the North. The design of landscapes that support an ecologically intensive agriculture creates opportunities for synergies between food production and ecosystem services. Most importantly, this can contribute to detoxify or food and the environment

Managing organic resources for soil amendment

Soil fertility management is a key issue for sustaining agricultural production in the tropics. Organic resources are important for short-term nutrient availability, as well as for longer-term maintenance of soil organic matter. For smallholder farmers, organic materials are an important source of nutrients, and necessary to manage soil fertility. However, the amount of organic material available on-farm is often limited in supply, and differs widely in quality. This is why the little that is available needs to be used as efficiently as possible

Towards understanding factors that govern fertilizer response in casave: lessons from East Africa

Information on fertilizer response in cassava in Africa is scarce. We conducted a series of on-farm and on-station trials in two consecutive years to quantify yield responses of cassava to mineral fertilizer in Kenya and Uganda and to evaluate factors governing the responses. Average unfertilized yields ranged from 4.2 to 25.7 t ha-1 between sites and years. Mineral fertilizer use increased yields significantly, but response to fertilizer was highly variable (-0.2 to 15.3 t ha-1). Average yield response per kg applied nutrient was 37, 168 and 45 and 106, 482 and 128 kg fresh yield per kg of applied N, P and K, respectively in 2004 and 2005. Fertilizer response was governed by soil fertility, rainfall and weed management, but was not influenced by variety, pest and disease pressure and harvest age. Relative N and K yields were positively correlated to SOC and exchangeable K, while response to fertilizer decreased on more fertile soils. Still, fertilizer response varied widely on low fertility soils (e.g. on soils wit

Managing soil fertility diversity to enhance resource use efficiencies in smallholder farming systems: a case from Murewa District, Zimbabwe

Smallholder farms in sub-Saharan African exhibit substantial heterogeneity in soil fertility, and nutrient resource allocation strategies that address this variability are required to increase nutrient use efficiencies. We applied the Field-scale resource Interactions, use Efficiencies and Long-term soil fertility Development (FIELD) model to explore consequences of various manure and fertilizer application strategies on crop productivity and soil organic carbon (SOC) dynamics on farms varying in resource endowment in a case study village in Murewa District, Zimbabwe. FIELD simulated a rapid decline in SOC and maize yields when native woodlands were cleared for maize cultivation without fertilizer inputs coupled with removal of crop residues. Applications of 10 t manure ha-1 year-1 for 10 years were required to restore maize productivity to the yields attainable under native woodland. Long-term application of manure at 5 and 3 t ha-1 resulted in SOC contents comparable to zones of high and medium soil fertility observed on farms of wealthy cattle owners. Targeting manure application to restore SOC to 50–60% of contents under native woodlands was sufficient to increase productivity to 90% of attainable yields. Short-term increases in crop productivity achieved by reallocating manure to less fertile fields were short-lived on sandy soils. Preventing degradation of the soils under intensive cultivation is difficult, particularly in low input farming systems, and attention should be paid to judicious use of the limited nutrient resources to maintain a degree of soil fertility that supports good crop response to fertilizer applicatio

Yield and Quality of Sequentially Grown Cherry Tomato and Lettuce under Long-Term Conventional, Low-Input and Organic Soil Management Systems

Besides to conventional fertiliser use, organic and low-input technologies are being increasingly used for soil management in vegetable production. However, different factors operating during crop growth (i.e. the pre-harvest factors) and related to soil properties may affect yield and quality of vegetable crops. The present research aimed to study how different soil management regimes influence soil physical and chemical properties and how these affect yield and some quality traits of two major vegetable crops. We focused on lettuce, a major crop in the area under both conventional and organic production, and on cherry tomato, which is increasingly grown in organic vegetable systems. The soil management systems were: conventional (CM), following recommended fertilisation rates; low input (LI), using minimum fertilisation rates as needed; and organic, including manure application (MA) and incorporation of oat as green manure (GM) and of maize residues (MR). Preliminary results indicate that after 7 years of rotating vegetable crops soil properties tended to improve with some systems: e.g. lower bulk density and higher porosity with MA; higher cation exchange capacity (CEC) with MA and CM. After these 7-year pre-treatments, significant differences in crop growth and yields were observed for cherry tomato and lettuce grown under different production systems, but not for the overall quality indicators. The highest yields of cherry tomato were achieved with CM and MA, due to increased number of fruits per plant, with no differences in fruit weight. Lettuce yields were generally higher with CM compared to LI, although the effect was different for different types of lettuce: the leafy type produced higher yields per area whereas the Latin type produced heavier individual plants. Under organic soil management systems, the relative survival and the visual quality of the Latin type was reduced by Botrytis cinerea infections. The results of the study indicated that plots that underwent long-term applications of 15 t hamanure every two years produced similar yields than conventional systems and had comparable soil fertility attributes. However, the visual quality of the end product may be affected under organic systems. As observed for lettuce, cultivar choice may also play a role, since some lettuce types appeared to be more suitable for such systems than other

Exploring land use scenarios by long-term simulation of soil organic matter in central Argentina

Frequently, agriculture intensification by means of high-input technologies and agroecosystem simplification led to unsustainable farming systems. Increasing spatial-temporal diversity in agroecosystems has been shown as a promising alternative for restoring degraded land. A methodological approach is discussed here, based on preliminary results of experiences in a region of strong biophysical gradients. The CENTURY model is validated under local conditions and used as monitoring tool. The impact of an increased agrodiversity on soils with contrasting inherent properties is exemplified by running three land use scenarios for two case-study sites for the next 50 years and evaluating trends in soil organic matter (SOM) contents. Field survey and simulation results suggested that: (1) reference values for SOM levels for monitoring soil health should be defined considering main agroecological factors; (2) simulation models may help identifying adequate ranges of variation for them; (3) and model outputs may complement experimentation and represent a didactic tool to be used for decision-making and knowledge-transfer processes