In modern horticulture on artificial substrates effective systems for plant nutrition have been developed for many crops. The efficiency of nutrient use, however, is often low: on average 40 to 80% of all nutrients applied to tomato and cucumber grown on rockwool slabs is leached from the root environment. In soilless systems only the volume of nutrient solution provides buffering for nutrients when supply and uptake of nutrients are not equal. From a simple model of water and nutrient balance for a well-mixed nutrient solution system, relations between nutrient and water leaching were derived, explaining the low nutrient use efficiencies obtained in practice on soilless media. Improvement of nutrient use efficiency largely depends on improving synchronisation of nutrient supply with nutrient demand. The ratio of “uptake concentration” (current nutrient uptake rate divided by current water uptake rate) and the nutrient concentration in the system is a key parameter. Understanding of fluctuations in this ratio, as determined by daily rhythms, weather conditions and growth stages, may lead to intensive plant nutrition systems that are not only effective, but also efficient.
Tag: nutrients
Sesbania tree fallows on phosphorus-deficient sites: Maize yield and financial benefit
Rotation of Sesbania sesban (L.) Merr., a fast-growing N2-fixing tree, with maize (Zea mays L.) has potential for increasing fertility of tropical soils, where fertilizer use by resource-poor farmers is limited. At two sites in Kenya (Ochinga, with a Kandiudalfic Eutrudox soil, and Muange, with a Kandic Paleustalf), we compared maize yields and financial returns for (i) sesbania grown for three or four seasons followed by three maize crops (sesbania fallow), (ii) one maize crop followed by natural regrowth of vegetation for three seasons and then three maize crops (natural fallow), and (iii) maize monoculture for seven seasons. After the fallows, plots were split with and without added P. Maize responded to P at both sites. Cumulative grain yields for seven seasons of maize monoculture were 8.4 Mg ha1 at Ochinga and 5.6 Mg ha1 at Muange. They were comparable to cumulative maize yields for sesbania fallow (Ochinga, 10.6 Mg ha1 Muange, 4.5 Mg ha1) and natural fallow (Ochinga, 7.7 Mg ha1; Muange, 4.2 Mg ha1), even though maize was grown for only three or four seasons in the fallow treatments. Sesbania fallow was financially attractive at Ochinga (500 mm rain in each season) but not at Muange, where low rainfall (<300 mm in each posffallow season) limited maize yield. Phosphorus fertilization of maize at Ochinga increased (P < 0.2) net benefit for sesbania fallow. Improved fallows have potential to supply nutrients to crops, but they are unlikely to eliminate the need for P fertilizers on P-deficient soils.
Agroforestry and the achievement of the Millennium Development Goals
The Millennium Development Goals (MDGs) of the United Nations (UN) are at the heart of the global development agenda. This chapter examines the role of agroforestry research and development (R&D) in light of the MDGs. It reviews some of the ways in which agroforestry is substantively assisting to achieve the goals and discusses how the agenda can be realigned to further increase its effectiveness in helping developing countries to meet their MDG targets. Promising agroforestry pathways to increase on-farm food production and income contribute to the first MDG, which aims to cut the number of hungry and desperately poor by at least half by 2015. Such pathways include fertilizer tree systems for smallholders with limited access to adequate crop nutrients, and expanded tree cropping and improved tree product processing and marketing. These advances can also help address lack of enterprise opportunities on small-scale farms, inequitable returns to small-scale farmers especially women), child malnutrition, and national tree-product deficits (especially timber). The rate of return to investment in research on tree crops is quite high (88%)
Nitrogen and phosphorus in African soils – what role for agroforesty?
The article looks at the role of agroforestry in nutrient cycling and focuses on the two main nutrients that limit production, namely nitrogen and phosphorus in a small-holder production system based on maize in Africa.
Interactions of organic materials with phosphate rocks and triple superphosphate
Tithonia diversifolia in western Kenya: relationship of tissue phosphorus concentration to soil phosphorus
Tithonia diversifolia, a shrub in the family Asteraceae, is widely distributed alongfarm boundaries in the humid and subhumid tropics of Africa. Green biomass of tithonia hasbeen recognized as an effective source of nutrients for lowland rice (Oryza sativa) in Asia andmore recently for maize (Zea mays) and vegetables in eastern and southern Africa. This paperreviews the potential of tithonia green biomass for soil fertility improvement based on recentresearch in western Kenya. Green leaf biomass of tithonia is high in nutrients, averaging about3.5% N, 0.37% P and 4.1% K on a dry matter basis. Boundary hedges of sole tithonia can produceabout 1 kg biomass (tender stems + leaves) m–1yr–1on a dry weight basis. Tithonia biomassdecomposes rapidly after application to soil, and incorporated biomass can be an effective sourceof N, P and K for crops. In some cases, maize yields were even higher with incorporation oftithonia biomass than with commercial mineral fertilizer at equivalent rates of N, P and K. Inaddition to providing nutrients, tithonia incorporated at 5 t dry matter ha–1can reduce P sorptionand increase soil microbial biomass. Because of high labor requirements for cutting and carryingthe biomass to fields, the use of tithonia biomass as a nutrient source is more profitable withhigh-value crops such as vegetables than with relatively low-valued maize. The transfer oftithonia biomass to fields constitutes the redistribution of nutrients within the landscape ratherthan a net input of nutrients. External inputs of nutrients would eventually be required to sustainproduction of tithonia when biomass is continually cut and transferred to agricultural land
Tithonia diversifolia as a green manure for soil fertility improvement in western Kenya: A review
Tithonia diversifolia, a shrub in the family Asteraceae, is widely distributed along farm boundaries in the humid and subhumid tropics of Africa. Green biomass of tithonia has been recognized as an effective source of nutrients for lowland rice (Oryza sativa) in Asia and more recently for maize (Zea mays) and vegetables in eastern and southern Africa. This paper reviews the potential of tithonia green biomass for soil fertility improvement based on recent research in western Kenya. Green leaf biomass of tithonia is high in nutrients, averaging about 3.5% N, 0.37% P and 4.1% K on a dry matter basis. Boundary hedges of sole tithonia can produce about 1 kg biomass (tender stems + leaves) m1 yr1 on a dry weight basis. Tithonia biomass decomposes rapidly after application to soil, and incorporated biomass can be an effective source of N, P and K for crops. In some cases, maize yields were even higher with incorporation of tithonia biomass than with commercial mineral fertilizer at equivalent rates of N, P and K. In addition to providing nutrients, tithonia incorporated at 5 t dry matter ha1 can reduce P sorption and increase soil microbial biomass. Because of high labor requirements for cutting and carrying the biomass to fields, the use of tithonia biomass as a nutrient source is more profitable with high-value crops such as vegetables than with relatively low-valued maize. The transfer of tithonia biomass to fields constitutes the redistribution of nutrients within the landscape rather than a net input of nutrients. External inputs of nutrients would eventually be required to sustain production of tithonia when biomass is continually cut and transferred to agricultural land.
Tithonia diversifolia: variations in leaf nutrient concentration and implications for biomass transfer
Green leaf biomass of Tithonia diversifolia is high in nutrients and recognised as a potential source of nutrients for crops. We conducted a field survey in western Kenya to determine the variation in leaf nutrient concentrations in tithonia grown in naturalised hedges and agricultural fields, and to examine whether leaf nutrient concentrations were related to soil nutrient status. Leaf P and K concentrations were higher in naturalised hedges (3.2 g P kg1 and 35 g K kg1) than in unfertilised fields (2.2 g P kg1 and 23 g K kg1). The critical level of 2.5 g P kg1 for net P mineralisation was exceeded by > 90% of the leaves from hedges, but by only 14% from unfertilised fields. Leaf P and K concentration increased linearly with increasing natural logarithm of anion resin extractable soil P and exchangeable soil K, respectively. However, at the same levels of soil available P and K, field-grown tithonia consistently produced lower leaf P and K concentrations than that grown in hedges. This study indicates that biomass from tithonia planted on nutrient-depleted soils would be a less effective source of P and K, via biomass transfer, than tithonia from naturalised hedges.
Testing the safety-net role of hedgerow tree roots by 15N placement at different soil depths
Trees which root below crops may have a beneficial role in simultaneous agroforestry systems by intercepting and recycling nutrients which leach below the crop rooting zone. They may also compete less strongly for nutrients than trees which root mainly within the same zone as crops. To test these hypotheses we placed highly enriched 15N-labelled ammonium sulphate at three depths in the soil between mixed hedgerows of the shallow-rooting Gliricidia sepium and the deep rooting Peltophorum dasyrrhachis. A year after the isotope application most of the residual 15N in the soil remained close to the injection points due to the joint application with a carbon source which promoted 15N immobilization. Temporal 15N uptake patterns (two-weekly leaf sub-sampling) as well as total 15N recovery measurements suggested that Peltophorum obtained more N from the subsoil than Gliricidia. Despite this Gliricidia appeared to compete weakly with the crop for N as it recovered little 15N from any depth but obtained an estimated 44–58% of its N from atmospheric N2-fixation. Gliricidia took up an estimated 21 kg N ha–1 and Peltophorum an estimated 42 kg N ha–1 from beneath the main crop rooting zone. The results demonstrate that direct placement of 15N can be used to identify N sourcing by trees and crops in simultaneous agroforestry systems, although the heterogeneity of tree root distributions needs to be taken into account when designing experiments.
Dynamics of banana-based farming systems in Bukoba district, Tanzania: changes in land use, cropping and cattle keeping
The spatial and temporal changes of land use, cropping patterns and cattle keeping were assessed for the period 1961–1999 in Kyamtwara division, Bukoba district, Tanzania. The assessment was based on interpreting aerial photographs, surveys and a review of historical statistical data. The area of grassland declined by 40% with a concomitant increase in annual crop fields and forest of 225 and 36%, respectively. The cropping pattern changed from a predominance of banana/coffee/beans to a complex mixed cropping of banana/coffee/beans/maize and root crops in the homegarden, and increased cultivation of maize and root crops in pure stands. Farmers stopped cultivating sorghum and finger millet. The population of indigenous cattle decreased by 50% and an equal percentage of dairy cattle was introduced, but cattle-owning households decreased by 85%. Nutrient balances of homegardens ranged between 27 and 17 kg N ha1 yr1, 1 and 7 kg P ha1 yr1 and 5 and 12 kg K ha1 yr1, with the positive balances achieved by resource-rich households. Nutrient balances of crops in pure stand ranged between 15 and 2 kg N ha1 yr1, 2 and 1 kg P ha1 yr1 and 14 and 1 kg K ha1 yr1, with more negative balances observed with maize, implying that soil nutrient stocks are decreasing. Increasing population density, coupled with an unequal distribution of resources among households, land tenure, economic policies and poor crop markets were identified as major causal factors of the above changes. Reversing soil fertility decline requires external inputs of nutrients. Within the current poor economic situation of the farming community, different potential soil fertility improvement strategies, including exploitation of N2-fixing legumes are discussed.