Apparent Nitrogen Recovery in Milk and Early Dry Season Nitrous Oxide Emission Factors for Urine Deposited by Dual-Purpose Cattle on Different Soil Types

Pasture conditions influence the nutrients use efficiency and nitrogen (N) losses from deposited excreta. Part of the N is lost as nitrous oxide (N2O), a potent greenhouse gas. The objective of this study was to characterize apparent N recovery in milk of dual-purpose cattle and to quantify N2O emissions from the urine they deposit following grazing on Megathyrsus maximus cv. Mombasa. The N content in the grass and the milk produced by the cattle and the milk urea N (MUN) content were quantified in two contrasting regions of Colombia (Casanare and Atlántico). Dry matter intake (DMI) by the cattle was estimated using the Cornell Net Carbohydrate and Protein System. We used a closed static chamber technique to measure N2O emissions from soils in areas with and without urine patches (21 days in Atlántico and 35 Days in Casanare). Estimated DMI values were 11.5 and 11.6 kg DM day−1, milk production was 6.5 and 5.9 L day−1, apparent N recovery in milk was 24 and 23%, and the MUN content was 4.4 and 17.2 mg N dl−1 in Casanare and Atlántico, respectively. N applied to soil in the form of urine corresponded at rates of 20 and 64 g N m−2 and net cumulative N2O emissions were 350 and 20 mg N2O-N m−2 in Casanare and Atlántico, respectively. Despite low digestibility of offered diet, N recovery in milk was above the values reported at dairy cattle in tropical conditions. High urine-N inputs at Atlántico site did not result in high N2O emissions suggesting that the default Tier 1 emission factor (EF) which is based on N inputs would have overestimated urine-based N2O emissions in Atlántico. Comparing previous studies conducted in Colombia, we observed inter-regional differences by urine-based N2O emissions. This observation suggests that to increase certainty in estimating urine-based N2O emissions, Colombia needs to move toward more region-specific Tier 2 EF and reduce its dependence on the default IPCC Tier 1 EF. In addition, the adoption of Tier 2 EF in the cattle sector will facilitate accounting for the effect of animal diets on N2O inventories.

Coating of prilled urea with ecofriendly neem (Azadirachta indica A. Juss.) formulations for efficient nitrogen use in hybrid rice

A field experiment was carried out during the rainy season (June-October) of 1998 at the Research Farm of the Indian Agricultural Research Institute, New Delhi, India to study the effect of coating prilled urea with eco-friendly neem (Azadirachta indica A. Juss.) formulations in improving the efficiency of nitrogen use in hybrid rice. The experiment was laid out in a split-plot design with three replications. Two rice cultivars, hybrid rice (NDHR-3) and Pusa Basmati-1, formed the main plots, with the levels of nitrogen (0, 60, 120 and 180 kg N ha-1) and various forms of urea at 120 kg N ha-1 in the sub-plots. The results obtained in this study showed that the rice hybrid NDHR-3 performed significantly better than the scented variety Pusa Basmati-1 for almost all the agronomic traits tested (growth, yield attributes, grain and straw yields, nitrogen uptake and apparent N recovery) The advantage of grain yield in hybrid NDHR-3 was nearly 16 q/ha over Pusa Basmati-1. Increasing levels of nitrogen significantly increased the number of effective tillers hill-1, panicle length, panicle weight, grain and straw yields and nitrogen uptake, thereby revealing a significant decline in agronomic nitrogen use efficiency (NUE). Among the sources of N, Pusa Neem Golden Urea proved to be significantly superior to other sources with regards to panicle length, grain yield, N uptake, agronomic nitrogen use efficiency and apparent N recovery (%), indicating that coating urea with neem formulations not only increased the grain yield, NUE and apparent N recovery, but also helped to reduce the environmental hazards associated with the use of large amounts of urea.

Availability of manure slurry ammonium for corn using 15N-labelled (NH4)2SO4

The NH4+ fraction of animal manure slurry is often considered to be as available as fertilizer N to a crop; however, immobilization and losses via denitrification and NH3 volatilization may be higher in manured than in fertilized soil. The apparent N recovery and the 15N recovery methods were used for corn (Zea mays L.) grown in soil amended with dairy cattle slurry and NH4+ fertilizer to determine the source of the N taken up by corn plants. Manure slurry or (NH4)2SO4 fertilizer were applied at rates equivalent to 100 kg NH4+–N ha−1 in the greenhouse and the field. In the greenhouse, the apparent NH4+–N uptake by corn was 76 and 85% with animal manure slurries and NH4+ fertilizer, respectively. In the field, apparent N recovery of NH4+ from dairy cattle slurry and (NH4)2SO4 was 43 and 58%, respectively, whereas 15N recovery from the same treatments was 15 and 29%, respectively. The lower 15N recovery values compared with the apparent recovery values suggest that mineralization-immobilization turnover (MIT) occurred, and that MIT was greater in manured soil than in fertilized soil. A laboratory incubation study showed greater microbial biomass and more 15N immobilization in soil amended with dairy cattle slurry than in soil amended with fertilizer. Key words: Animal manure slurry, nitrogen, corn, N recovery, 15N microplots

Long term trends in total nitrogen of a vertisol subjected to zero-tillage, nitrogen application and stubble retention

The effects of conservation practices, zero-tillage and stubble retention, on long-term trends in total N (0-0.1 m depth) of a Vertisol used mainly for wheat cropping were studied in a semi-arid subtropical environment (28�12'S. and 152�06' E.) in Queensland. Trends in total N content of a Vertisoi (65% clay, pH 7.2) were discerned during a 22-year period of management practices including: zero-tillage (ZT) and conventional tillage (CT); stubble retention (SR) and stubble burning (SB); and fertilizer N application of nil (Nl), 23 kg N ha-1 yr-1 (N2) and 69 kg N ha-1 yr-1 (N3). Soil total N (0-0.1 m) declined under all treatments at an overall rate of 25f 2 kg N ha-1 yr-1 although after 22 years soil under ZT, SR and N3 treatments still contained higher soil total N than under CT, SB and N1 treatments. Apparent fertilizer N recovery in the soil-plant system was poor (34 64%) under CTSB, CTSR and ZTSB and ZTSR treatments, because N removed by the wheat crop was equivalent to less than 20% of fertilizer N in the first 12 years of management practices, due mainly to disease. Deep leaching losses of NO3-N was the likely factor for poor recovery of N. The ZTSR treatment showed better apparent N recovery than the CTSB treatment, most likely due to greater immobilization of fertilizer N, more N uptake in grain due to additional available soil water and hence less leaching losses of NO3-N. Under the current cultural practices, soil total N (0-0.1 m) may decline further to reach a steady state (about 1000 kg N ha-1). However, the apparent N recovery in the soil-plant system can be increased by disease control (for example, resistant cultivars and winter-summer crop rotations) and optimum utilisation of soil water (opportunity cropping) to minimize NO3-N leaching losses and to maximise production of crop biomass.

Efficiency of nitrogen use by dryland wheat in a subhumid region in relation to optimizing the amount of available water

SUMMARYThe effect of soil water supply on efficiency of N use in wheat and NO3-N accumulation in the soil profile was studied in a field experiment on loamy sand soil at Boothgarh in Hoshiarpur, Punjab, India in 1980/81. As the water supply increased from 509 to 548 mm, the response to N application increased by 11·5 kg grain/kg N and apparent N recovery by 11% at optimum N application rates. The increase in N recovery with additional water supply was related to the NO3-N use from the profile. The accumulation of NO3-N in the profile was related linearly to rate of N application but inversely to water supply up to an optimum value of 580 mm. Further increase in water supply did not increase fertilizer N use. If both the amount of moisture stored in the profile at sowing and the probable rainfall during the crop season are known, the efficiency of fertilizer N use can be predicted.