Decomposition and nutrient mineralisation of leaf litter in smallholder cocoa agroforests: a comparison of organic and conventional farms in Ghana

Purpose

Although litter decomposition and nutrient release patterns have been studied in cocoa agroforestry systems in general, studies focusing on organic and conventional cocoa systems are lacking which is critical as organic farms are particularly dependent on nutrient returns from decomposing litter.

Materials and methods

Dynamics in leaf litter decomposition and the mineralisation of macro- and micro-nutrients in organic and conventional cocoa agroforestry systems were studied using the litterbag technique for 12 months.

Results

The average monthly mass loss was more than two times higher on organic farms (9.2–14.4 g month^?1) compared to conventional farms (4.2–7.3 g month^?1) in the first five months. The annual rate of decomposition (k) was higher on organic farms (1.9) compared to conventional systems (1.4). The time required for 50% (t₅₀) and 99% (t₉₉) decomposition of leaf litter was both lower on organic farms (t₅₀?=?0.4 years, t₉₉?=?2.6 years) than conventional farms (t₅₀?=?0.5 years, t₉₉?=?3.5 years). The estimated k values for macro- and micro-nutrients on organic cocoa systems ranged from 2.3 for calcium to 4.5 for potassium compared to 1.6 (Ca) to 2.8 (K) on conventional farms. The k values of all nutrients (except nitrogen and phosphorus) were significantly greater on organic farms than conventional systems. The estimated k values for both litter decomposition and nutrient mineralisation correlated with soil pH and moisture content, but not initial litter chemistry.

Conclusions

Organic management of smallholder cocoa agroforestry systems enhanced leaf litter decomposition and nutrient mineralisation through improved soil conditions. Thus, organic management of cocoa agroforestry systems may contribute to sustainable cocoa production in smallholder systems through enhanced nutrient return from litter decomposition.

     

Beef production from the dairy herd: An analysis of mortalities

Extract

Utilization of surplus dairy animals for beef production has made notable progress in the past 2 to 3 years. In 1967 over 75,000 calves were reared for beef, increasing to about 150,000 in 1968 and probably more than 200,000 in 1969. This reflects, in part, the economic problems involved in international marketing of dairy products, but, in greater part, the accumulation and dissemination of technical knowledge derived from recent experimental work.     

Neospora abortion epidemic in a dairy herd

Neospora caninrm is a protozoan closely related to Toxoplasma gonclii. It was discovered only a few years ago, but it is now recognised as one of the most common and important causes of abortion in cattle. Brain lesions characteristic of Neospora infection have been found in about 25% of aborted foetuses submitted to diagnostic laboratories in New Zealand and overseas⁽¹⁾⁽²⁾. Average abortion rates due to Neospora on New Zealand farms have been estimated at 7% of pregnancies compared with 4% due to other causes⁽¹⁾. The upper range of abortion rates for Neospora was 17–30% compared to only 7–10% for other causes, showing that the economic effects of Neospora abortions on the more severely affected farms can be devastating.     

Tracing Dietary Mercury Histochemically,with Autometallography,through the Liver to the Ovaries and Spawned Eggs of the Spot,a Temperate Coastal Marine Fish

Abstract

Exposure to mercury (Hg) results in reproductive abnormalities and deficiencies in female fish. We traced the maternal assimilation and redistribution of dietary inorganic (HgII) and organic (MeHg) forms of Hg in a coastal marine fish, the Spot Leiostomus xanthurus. We conducted a 90-d laboratory experiment in which treatment Spot were fed muscle of Blue Marlin Makaira nigricans with elevated concentrations of Hg mixed with a commercial fish food, while control Spot were fed only commercial food pellets. Gonadal maturation was induced by shortening the photoperiod and increasing the temperature. Spawning was induced by intramuscular injection of human chorionic gonadotropin at 100 IU/kg. Solid-sampling atomic absorption spectrophotometry measured the total Hg (THg), HgII, and MeHg in Blue Marlin muscle. Autometallography located Hg-sulfide granules in the liver, ovaries, and spawned eggs, and densitometry provided comparisons of Hg-sulfide granules in the ovaries of treatment and control Spot. Overall, the intensity and prevalence of Hg-sulfide granules were greater in the liver, ovaries, and eggs from treatment Spot than in those from controls. The tissue and cellular distribution of Hg-sulfide granules differed.

Received November 18, 2016; accepted June 18, 2017 Published online August 11, 2017     

Habitat edge effects alter ant-guard protection against herbivory

Edge effects are among the most important drivers of species interactions in fragmented habitats, but the impacts of edge effects on multitrophic interactions are largely unknown. In this study we assess edge effects on species interactions within an ant–plant mutualistic system—where ants protect plants against herbivory—to determine whether habitat edges alter the amount of protection ants provide. We focus on a single species of myrmecophytic plant, Solanum americanum, and experimentally manipulate ant access to study plants in large-scale fragmented habitat patches at the Savannah River Site National Environmental Research Park, USA. In this system, S. americanum commonly hosts honeydew-producing aphids that are tended by ants, and grasshoppers are the primary herbivores. We measured edge effects on the per-plant abundance of aphids and protective ants as well as the abundance of grasshoppers in each habitat patch, and we evaluated levels of ant protection against herbivory near and far from habitat edges. We found that ants provided significant protection to plants far from edges, where herbivory pressure was highest, despite the fact that aphids and ants were least abundant on these plants. Conversely, ants did not provide significant protection near edges, where herbivory pressure was lowest and aphids and ants were most abundant. We conclude that a strong edge effect on grasshopper abundance was a key factor determining the amount of protection ants provided against herbivory. Future studies of the impacts of habitat fragmentation on ant–plant mutualisms will benefit from studies of ant behavior in response to herbivory threats, and studies of edge effects on other species interactions may also need to consider how species’ behavioral patterns influence the interactions in question.     

Prolactin and progesterone concentrations during early pregnancy and relationship to pregnancy loss prior to day 45

Eleven multiparous Quarter Horse and Thoroughbred mares were used to determine the plasma concentrations of progesterone and prolactin during early pregnancy and to examine the relationship of plasma progesterone and prolactin to pregnancy loss prior to d 45 of gestation. Plasma samples were collected at two day intervals beginning on d 14 of pregnancy (d 0 = ovulation) and countinued to d 80. Ovulation and pregnancy status were determined by ultrasonography. Four mares experienced pregnancy loss between d 28 and 44 and plasma samples were collected for 10 days beyond the detected loss. Seven mares had successful pregnancies (Term group).Plasma progesterone concentrations peaked by d 28 in the Term group, with individual peak values ranging from 14.9 to 31.9 ng/ml. Values then declined until d 36, followed by a rise until d 80. Prior to d 45 of gestation 5 of the 7 mares had a peak in excess of 15 ng/ml and 3 of these had brief periods, ranging fron 1 to 8 days when progesterone dropped to less than 2 ng/ml. The other 2 mares had peak plasma progesterone concentrations of less than 7 ng/ml, but maintained concentrations in excess of 2 ng/ml during this period.Within the mares experiencing pregnancy loss, 2 mares had a decline in plasma progesterone concentrations prior to pregnancy loss, while the other 2 had typical progesterone patterns beyond the detected loss. Differences in individual patterns of plasma progesterone concentration were observed in both groups (P<.01).Plasma prolactin concentrations ranged from less than .32 to 4.58 ng/ml in the Term group and from .31 to 1.9 ng/ml in the mares experiencing pregnancy loss. Differences in the individual patterns of prolactin secretion were observed in both groups (P<.01).A correlation between progesterone and prolactin was observed in the Term group between day 14 and 37 (P<.01, r²=.88).     

Adjunct treatment of equine respiratory disease complex (ERDC) with the propionibacterium acnes, immunostimulant, EqStim®

The effect of using Propionibacterium acnes, (EqStim®)^a as an adjunct to conventional therapy in the treatment horses with Equine Respiratory Disease Complex (ERDC) was evaluated. Of the 45 horses entering the study, 25 received EqStim® and conventional therapy while 20 horses (negative controls) received a carrier solution of 12.5% ethanol-saline and conventional therapy. At the end of the 14 day test period, 96% (24/25) of the horses treated with EqStim® and conventional therapy showed clinical improvement or complete recovery as compared to the control group in which 35% (7/20) of the horses (treated with conventional therapy and carrier) showed clinical improvement or complete recovery.