Nutrient management for intensive animal agriculture: policies and practices for sustainability

Abstract. The intensity of animal production around the world has increased substantially during the last half-century, which has led to large problems with the disposal of manures and waste waters. The focus of this paper is on the development of national policies to improve the nutrient management of concentrated animal feeding operations (CAFOs), where nutrients are invariably in surplus. To create proper nutrient management strategies for CAFOs, and to avoid environmental problems when surplus nutrients enter air, soil and water, we need to know the number of animals/birds in the unit, the quantity of manure/slurry produced, how this material is stored and handled and how much land is available for manure spreading. In this paper, we discuss the development of nutrient management strategies for CAFOs in Europe and North America, and the voluntary measures and environmental regulations related to this. For the planning of nutrient management to be comprehensive and efficient, we need expertise from several disciplines. This planning includes development of: animal diets that reduce the amounts of excreted nutrients; efficient storage and land application technologies; land application programmes to optimize yields and reduce nutrient losses; and strategies for use of excess manure outside the farm. Also, large-scale efforts involving many stakeholders (farmers, governments and private industry) are needed to solve problems with nutrient imbalances over the long term. Efforts along these lines include manure relocation, alternative uses of manures, nutrient trading, and a general extensification of animal agriculture. The overall guiding principle for policies and planning should be a balance of nutrients, on farms as well as at larger scales.     

A mechanistic model for the inhibiting effects of aluminium on the uptake of cations

Reported laboratory observations mention inhibiting effects of Al on uptake of cations. However, the diverse conditions of these experiments do not allow conclusions to be drawn about the extent of this inhibiting effect. An uptake model for Ca and Mg was therefore developed to study the interactions of Al and these cations. The model is based on surface complexation of the root surface with both specific adsorption reactions and exchange reactions included. Application of this model to experiments using a nutrient flux growth technique showed that the observed effects are well simulated. The behaviour of the model agreed with reported inhibiting effects of Al. The model showed that Al effects might be reversed by increased nutrient solution concentrations of cations. However, there exists a strong competitive interaction between Ca and Mg. Therefore, high Ca concentrations have a negative effect on the uptake of Mg. Plants with a high growth rate and a high shoot to root ratio appear to be more sensitive to Al effects than more slowly growing plants.     

Changes in the soil phosphorus status of agricultural land in the Netherlands during the 20th century

The Netherlands has a high cumulative mean phosphorus (P) balance. In the 20th century, cumulative mean P surpluses were ca. 4500 kg P₂O₅/ha. The annual surpluses have levelled off because of manure application limits from 1984 onwards. We report the effect of soil type, land use, and manure policy on changes in soil P of fields in the Netherlands during the 20th century. We used data (>5 million soil P tests) from the soil analysis laboratory BLGG AgroXpertus. Our results show that soil P has increased on average to fairly high and high ratings. Differences between regions and between land use have remained high from the first records in the 1930s; on arable land the increase continued until the end of our study period while on grassland no changes are evident in the last decades. In general regions with high livestock density have high soil P status. Soil P increased in the order bulbfields < grassland < arable land < maize land < horticulture, and in the order loess < clay < peat < sand soils. Spatial variations in P values reflect more the market value of the crops and regional availability of animal manure than (fertilizer) recommendations. Manure policy since 1984 has resulted in increasingly tight restrictions on P application from manure and fertilizers, but the effects are not yet clearly reflected in changed trends in soil P.     

Dryland maize yields and water use efficiency in response to tillage/crop stubble and nutrient management practices in China

Rainfed crop production in northern China is constrained by low and variable rainfall. This study explored the effects of tillage/crop residue and nutrient management practices on maize (Zea mays L.) yield, water use efficiency (WUE), and N agronomic use efficiency (NAE) at Shouyang Dryland Farming Experimental Station in northern China during 2003–2008. The experiment was set-up using a split-plot design with 3 tillage/crop residue methods as main treatments: conventional, reduced (till with crop residue incorporated in fall but no-till in spring), and no-till (with crop residue mulching in fall). Sub-treatments were 3 NP fertilizer rates: 105–46, 179–78 and 210–92 kg N and P ha⁻¹. Maize grain yields were greatly influenced by the growing season rainfall and soil water contents at sowing. Mean grain yields over the 6-year period in response to tillage/crop residue treatments were 5604, 5347 and 5185 kg ha⁻¹, under reduced, no-till and conventional tillage, respectively. Grain yields under no-till, were generally higher (+19%) in dry years but lower (−7%) in wet years. Mean WUE was 13.7, 13.6 and 12.6 kg ha⁻¹ mm⁻¹ under reduced, no-till, and conventional tillage, respectively. The no-till treatment had 8–12% more water in the soil profiles than the conventional and reduced tillage treatments at sowing and harvest time. Grain yields, WUE and NAE were highest with the lowest NP fertilizer application rates (at 105 kg N and 46 kg P ha⁻¹) under reduced tillage, while yields and WUE tended to be higher with additional NP fertilizer rates under conventional tillage, however, there was no significant yield increase above the optimum fertilizer rate. In conclusion, maize grain yields, WUE and NAE were highest under reduced tillage at modest NP fertilizer application rates of 105 kg N and 46 kg P ha⁻¹. No-till increased soil water storage by 8–12% and improved WUE compared to conventional tillage, thus showing potentials for drought mitigation and economic use of fertilizers in drought-prone rainfed conditions in northern China.     

Genetic diversity for nitrogen use efficiency in spinach (Spinacia oleracea L.) cultivars using the Ingestad model on hydroponics

Spinach is a leafy vegetable that requires a high N fertilization to have a satisfactory yield and quality, in part because it has poor nitrogen use efficiency (NUE). Therefore, there is a need to breed for cultivars with an excellent NUE. To this end the genetic diversity for NUE-related traits was studied in a diverse set of commercial cultivars. This set was evaluated in a hydroponic system using the Ingestad model; the system was set at a relative growth rate of 0.14 and 0.18 g g^?1 day^?1 (low and high N, respectively). Experiments were performed at low and high plant density. Traits monitored for single plants included fresh and dry weight, leaf area, specific leaf area, dry weight ratio between root and shoot, and chlorophyll content. The high density experiment showed more genotypic variation for the observed traits than the low density one. Biomass production was considerably lower at low than at high N. Path analysis revealed that leaf area had the highest direct effect on NUE, while specific leaf area was an important trait determining variation in NUE at low N. Slow and fast growing genotypes were shown to use different strategies to utilize N, and these strategies are expressed differently at high and low N availability. This indicates that improving spinach for NUE is feasible using the analysed genotypes as source material, and different strategies can be targeted for adaptation of spinach cultivars to low N conditions.     

Effects of variation in rainfall on rainfed crop yields and water use in dryland farming areas in China

Crop production in the dryland farming areas of northern China is constrained by low and variable rainfall. This article presents the analysis of the relationships between variations in rainfall and yields of winter wheat and spring maize. The analysis is based on data from both several short-term and our ongoing long-term field experiments in dryland farming research projects in Tunliu, Linfen, Shouyang, and Luoyang. Grain yields of wheat and maize ranged from 1,548 to 5,169 and from 2,612 to 8,789 kg ha^-1 respectively, with differences up to above 200% (between dry and wet years). Wheat yields are sensitive to growing season rainfall but also correlated to water use (ET), whereas maize yields are sensitive to the critical time of water supply (especially June rainfall) but not correlated to ET. The ratio of grain yields to soil water at sowing is an important indicator, showing close relationships between yields and soil water-related ratio within the rainfed crops site. Comparison between the indices of water use efficiency (WUE) and precipitation use efficiency (PUE) suggests that the index WUE is more grain-related indicator than the PUE used for assessing rainfed crop water use by both maize and wheat. The index PUE should be used in caution, especially for wheat crops in dry years. Our results indicate that options to alleviate crop moisture stress must be tailored to the rainfall pattern. This holds especially for conservation tillage with response nutrient management practices that aim at enhancing water use efficiency.     

Ammonia volatilization from Vertisols

Farmers want to minimize losses of nitrogen (N) by volatilization of ammonia when adding fertilizers and improve fertilizer recovery of N by plants. We aimed to quantify the losses of N through NH₃ volatilization as affected by soil moisture content, type of fertilizer, and placement method in Vertisols in Kenya, and conducted three experiments for the purpose under controlled conditions in the laboratory. We found that NH₃-N losses were greatest at 80% water holding capacity, which we ascribed to the ready availability of water to dissolve the fertilizer at that water content. The soil's cation exchange capacity (CEC) did not influence volatilization, whereas the soil's pH indicated the potential of the soil to volatilize ammonia. Ammonia losses from the fertilizers were in the order urea > ammonium sulphate > ammonium nitrate applied. Incorporating fertilizer within the 0–5 cm soil layer more than halved NH₃ volatilization but did not prevent it completely. These results indicate that soil pH, rather than CEC, is the main inherent characteristic influencing ammonia volatilization from Vertisols. Ammonium-based fertilizers should be incorporated within the 0–5 cm soil layer, or preferably somewhat deeper, to avoid losses via NH₃ volatilization, particularly in alkaline soils. Nitrate fertilizers are preferable to urea where the risks of NH₃ volatilization are large, provided due consideration is given to denitrification risks.