N. van Duivenbooden

Nitrogen, phosphorus and potassium relations in five major cereals reviewed in respect to fertilizer recommendations using simulation modelling

In land use plans, fertilizer recommendations are indispensable to avoid soil nutrient depletion or soil water pollution. Nutrient relations of five cereals have been evaluated on the basis of a literature review with the aim of arriving at such fertilizer recommendations at regional level. Nutrients considered were nitrogen, phosphorus and potassium for millet, sorghum, maize, rice and wheat. The relevant nutrient relations are fertilizer nutrient application to nutrient uptake, and nutrient uptake to crop yield. In addition, post-anthesis nutrient uptake is considered. Subsequently, obtained results are used in simulation modelling exercises to calculate the time required to attain an equilibrium nutrient balance and to investigate the effect of erosion control and straw recycling. Although fertilizer requirements could be assessed for each of the five cereals, monitoring of nutrient supply from natural sources remains necessary. Moreover, research on fertilizer use should focus on improvement of fertilizer recoveries and multiperiod models for both N and P uptakes by crops to allow quantitative land use planning where the time scale is included.

Impact of climate change on agricultural production in the Sahel - Part 2. Case study for groundnut and cowpea in Niger

During the last 30 years, the climate of the West African Sahel has undergone various changes, especially in terms of rainfall. This has large consequences for the poor-resource farmers depending mainly on rainfed agriculture. This paper investigates the impacts of current climate variability and future climate change on groundnut and cowpea production in Niger for three major agricultural regions, including the groundnut basin.Niger was one of the largest West African groundnut producing and exporting countries. Groundnut production – as a cash crop – dropped fromabout 312,000 tons in the mid 1960s (about 68% exported) to as low as 13,000tons in 1988 and increased again to 110,000 tons in 2000. Cowpea, a food crop, showsa different tendency, going from 4,000 tons in the mid fifties to a maximum of 775,000 tons in 1997, and its cultivated area is still increasing. It is also a cash crop in local economies (especially for women).To highlight the impact of climate change on groundnut and cowpea production (significantly determined by rainfall in July, August and September), the following components of the rainfall regime were calculated for the period 1951–1998: mean annual and monthly rainfall, beginning, end and lengthof the rainy season, number of rainy days per month, amount of rainfall per rainy day and the maximum length of dry spell per month. Three sub-periods whose duration varied per region were defined: for Dosso 1951–1968,1969–1984 and 1985–1998; for Maradi 1951–1970, 1971–1987 and1988–1998; and for Zinder 1951–1966, 1967–1984 and 1985–1998. A change in rainfallregime components was observed between the three sub-periods, which were characterized in chronological order by wet, dry and intermediate conditions. To assess the impact of climate variability and change on groundnut and cowpea production, a statistical modeling approach has been followed, based on thirteen predictors as described and discussed in the preceding paper. Climate change is mimicked in terms of reduced total amount of rainfall for the three main rainfall months and an increased temperature, while maintaining other significant predictors at a constant level. In 2025,production of groundnut is estimated to be between 11 and 25% lower, while cowpeayield will fall maximally 30%. Various strategies to compensate thispotential loss are presented for the two crops.

Fertility management and landscape position: farmers' use of nutrient sources in western Niger and possible improvements

Poor millet growth and yields in Niger are commonly attributed to rainfall deficits and low soil nutrient content. Land management by local farmers is done as a function of soil types, crops, and available resources. Farmer management practices in millet fields located on four different landscape positions were studied in a village in western Niger located near the 600 mm isohyet. Average distance from homestead to field was 980 m, with fields in the valley bottom much closer (average 225 m) and fields on the plateau much further (average 2300 m). Farmers considered the valley and plateau fields slightly more fertile than the other fields, but rainfall infiltration on plateau fields is often relatively poor. Nitrogen and phosphorus contents in the soil were highest on the less intensively cropped plateaus. More than 50% of the fields did not receive any applied nutrients other than during livestock grazing of leftover stover. Manure application was done through corralling in only four of the fields studied (20%), out of which three were farmed by Fulani using their own herds for manuring. There was no significant effect of landscape unit on yield, though yields in the valley and on the upper slope were slightly higher than average. Millet grain yields, soil carbon and soil phosphorus decreased significantly with distance from the living quarters. This may be because manuring usually takes place close to home (average distance in 1997 <200 m). Manure application increased millet grain production from 126 kg ha−1 to 316 kg ha−1 in 1997. Manuring yielded more than 1000 kg ha−1 in 1996, when rainfall was much more favourable. Fallowed fields yielded an average 143 kg ha−1 of millet grain in 1997, with fallow taking place an average of 1640 m from the homestead. Another soil fertility management practice included use of millet threshing residues in fields adjacent to the village. There was no chemical fertilizer application. Any improvement to the system will require the solution of existing constraints limiting the integration of livestock and crops and/or limiting the input of external sources of nutrients in Niger. These limitations can include lack of land to allow fallowing practices and/or grazing; local non-availability of mineral fertiliser; lack of capital to buy fertiliser, due in part to low millet prices; lack of means of transport for inputs; but also lack of means for pest control and lack of labour for sowing, weeding and thinning. Initial improvements may be made by making more efficient use of the available manure, through much lighter and slightly more frequent manuring of much larger areas.

Impact of inorganic fertilizer availability on land use and agricultural production in the Fifth Region of Mali. 1. Methodology and basic data.

An interactive multiple goal linear programming model has been developed for analysis of agricultural development options in a semiarid region in Mali. Natural and human resources have been quantified, constraints identified and the relations between agricultural activities described explicitly at both regional level and the level of agro-ecological zones.Animal husbandry and cropping system have been defined in a target-oriented way taking into account quantified aspects of sustainability. For crops this implies the requirement that the amounts of the macronutrients N, P and K in the rootable layer of the soil are safeguarded in the long run by nutrient applications. External inputs to realize predetermined target yields have been specified to compile quantitative input-output tables.Goals and goal-variables to be optimized in the model have been defined after consultations with various stakeholders in the region. Goal restrictions have been established through the interactive approach of the model.

Impact of inorganic fertilizer availability on land use and agricultural production in the Fifth Region of Mali. 2. Scenario definition and results.

A multiple goal linear programming model has been used to explore the impact of inorganic fertilizer availability on land use, crop and livestock production in the Fifth Region of Mali. Three scenarios have been examined with restricted, intermediate and unrestricted inorganic fertilizer availability. Marketable crop production was maximized under various restrictions and limiting values of other goals, such as a minimum regional gross revenue, and on the basis of sustainable agricultural activities. Results are discussed at both regional and subregional levels.Unrestricted inorganic fertilizer availability allows a substantial increase in crop production. In normal years, the food needs in 8 of the 11 agro-ecological zones distinguished in the region are met, whereas this holds for 7 out of 11 in the other two scenarios. In dry years, food needs can only be met if, in addition to unrestricted inorganic fertilizer availability and emigration, some sacrifices (e.g. lower regional gross revenue) are accepted.In all three scenarios, available animal manure has to be utilized completely and supplemented by substantial amounts of imported inorganic fertilizer, largely exceeding current total national imports.In a post-model analysis aspects are examined that could not be incorporated in the model. To stimulate the use of inorganic fertilizer, a reduction in its farmgate price is recommended. Income generated outside the agricultural sector is required to pay for subsidies on fertilizers and reduce risks in animal marketing.

Grazing as a tool for rangeland management in semiarid regions: a case study in the north-western coastal zone of Egypt

Abstract Subshrubs are the dominant plant type of rangeland in the north-western coastal zone of Egypt. As animal husbandry depends to a large extent on this feed source, effects of grazing on plant growth were investigated. Experimental results showed that grazing extends the growing period of subshrubs. the mechanism underlying this phenomenon is lower water use by plants in the rainy season and the consequent higher availability in the dry season. Owing to the characteristic growth form of the subshrubs, leaves are protected inside their dense structure, ensuring plant growth while grazing takes place. Simulations suggested that water storage in deeper soil layers is a function of grazing intensity and annual precipitation. It is suggested that a considerable grazing pressure is necessary to maintain the rangeland. Regeneration of the rangeland is a problem and physical removal (firewood) is a greater danger to its persistence than is grazing.

Fertilization of millet cv Souna III in Senegal: dry matter production and nutrient uptake.

In a fertilizer and manure experiment, millet was grown under four treatments (no fertilizer or manure, farmyard manure, chemical fertilizer, and both). Grain yield and total aboveground biomass production of the unfertilized plot were relatively high. The observed differences in total dry matter production must be attributed to differences in nutrient availability, as amount of rainfall and its distribution were favourable. Results show only small differences in distribution of dry matter among the various plant organs between the best and the non-fertilized treatments.Nutrient supply from natural sources, defined as crop content of N, P, and K at maturity without fertilizer application, amounted to 104, 16 and 103 kg ha−1, respectively, which are very high values.Total uptake of calcium and magnesium is related to that of potassium, as the combined content of these three elements is linearly related to total aboveground biomass production. Minimum removal of nitrogen and phosphorus per ton grain dry matter amounts to 29 and 4kg, respectively, and 9 kg potassium per ton total aboveground dry matter. A possible double function of phosphorus as element of structural biomass and for maintenance of electro-neutrality is discussed.