Sheep manure can partially replace urea in Pakchong forage, coastal trial shows

A field experiment in coastal Bangladesh has found that part of the urea nitrogen normally applied to Pakchong forage grass can be replaced with sheep manure without sacrificing agronomic performance, and with measurable benefits for some growth traits. The study, conducted at Khulna University between February and May 2021, tested five nitrogen management strategies on Pakchong (Pennisetum purpureum × Pennisetum americanum), a high-yielding hybrid grass prized across the tropics for its biomass and nutritional value. The results suggest that in a region where salinity and waterlogging already constrain agriculture, farmers may be able to reduce their dependence on chemical nitrogen fertilizer while keeping forage yield and quality within acceptable limits.

The research team arranged the trial in a randomized complete block design with three replications and fifteen plots, each measuring ten square meters. Five treatments were compared on an equal-nitrogen basis: an unfertilized control, a treatment receiving the full recommended nitrogen dose from urea, and three treatments in which one third, two thirds, or all of the nitrogen came from sheep manure instead. The recommended dose corresponded to 28.75 kilograms of nitrogen per hectare, equivalent to 62.5 kilograms of urea per hectare. Because all fertilized treatments received the same total nitrogen, any differences among them could be attributed to the source of the nitrogen rather than to the amount applied. Phosphorus and potassium from triple superphosphate and muriate of potash were adjusted across treatments to account for the nutrients contributed by the manure.

The sheep manure itself was collected from a local sheep improvement project, air-dried, crushed, and cleaned of stones and plant residues before application. Chemical analysis of the dried manure showed it contained 0.28 percent nitrogen, 0.0050 percent phosphorus, and 1.2536 percent potassium. Half of all fertilizers were incorporated into the soil six days before planting, and the remainder was applied fifteen days after planting. Pakchong cuttings were planted on 20 February 2021 in four rows per plot, with eighteen cuttings per row spaced thirty centimeters apart. The soil at the site was slightly alkaline, with a pH of 8.10 and an electrical conductivity of 4.40 dS per meter, and total nitrogen and available phosphorus were both very low before the experiment began.

The crop was harvested twice, at sixty and ninety days after planting, and researchers recorded a suite of agronomic traits including plant height, leaf number, leaf length, leaf width, tiller number, biomass, stem diameter, nodal distance, and root length. Proximate composition, covering dry matter, crude protein, crude fiber, ether extract, and ash, was determined for both harvests. Data were analyzed using analysis of variance in SAS, with significance assessed at the five percent level.

At the first harvest, the clearest treatment effect appeared below ground. Root length differed significantly among treatments, with the highest value, 34.90 centimeters, recorded in the mixed treatment containing 66.67 percent sheep manure nitrogen and 33.33 percent urea nitrogen. The lowest root growth occurred under sole sheep manure, which the authors interpret as a sign that complete replacement of urea may limit early nutrient availability, since manure releases its nitrogen gradually while urea supplies it immediately. Plant height, leaf traits, tiller number, stem diameter, and biomass showed no statistically significant differences at this stage, although the best numerical values for plant height, leaf length, leaf width, and stem diameter were found in the treatment with two thirds urea and one third manure.

By ninety days after planting, the mixed-source treatment had become the standout performer above ground as well. Tiller number was highly significantly affected by the nitrogen source combination, with the mixed treatment producing the highest count at 10.41 tillers. Stem diameter also varied significantly, ranging from 4.03 to 4.82 centimeters, again with the highest value in the mixed treatment. The authors note that because total nitrogen was held constant, these late-season responses reflect the effect of nitrogen source rather than fertilizer dose. Plant height, root length, leaf traits, nodal distance, and biomass were not significantly affected at the second harvest, though the highest numerical values for plant height, root length, leaf length, and biomass were again recorded in the mixed treatment.

Nutritional composition told a more nuanced story. At sixty days after planting, dry matter and crude fiber differed highly significantly among treatments, both peaking in the mixed treatment, while ash content varied significantly and was highest, at 16.55 percent, under sole sheep manure. Crude protein was not significantly affected at this early stage, with its highest value, 16.29 percent, appearing in the full urea treatment. At ninety days, however, none of the nutrient parameters differed significantly among treatments. The authors attribute this disappearance of treatment effects to the overriding influence of plant maturity, combined with the slow mineralization pattern of sheep manure, which narrows the contrast between nitrogen sources as the crop ages.

Maturity effects were evident across the board. Crude fiber and dry matter increased as the forage matured, while crude protein declined, falling to a range of 10.16 to 13.87 percent at the second harvest. This pattern agrees with earlier studies on elephant grass and hybrid Pennisetum, which report lower crude protein and higher structural fiber at longer harvest intervals. The authors caution that the numerically higher crude fiber and crude protein observed under full urea at ninety days, and the higher ether extract and dry matter under the mixed treatment, should be treated only as descriptive trends rather than demonstrated treatment advantages, since none of the differences reached statistical significance.

The practical takeaway is that partial substitution of urea with sheep manure can reduce reliance on inorganic nitrogen without clear loss of agronomic performance under the tested coastal conditions. The mixed treatment with two thirds sheep manure nitrogen and one third urea nitrogen gave the most consistent overall response, particularly through improved tillering and competitive stem diameter late in the season, while sole sheep manure was less favorable for early root development. The authors frame this as a provisional recommendation, noting that the study covered a single season, a single location, and a production window of only ninety days, and that it did not quantify post-harvest soil changes or assess economics.

The broader context gives the findings weight. Bangladesh’s southwest coastal zone covers roughly 29,000 square kilometers, with more than 30 percent of cultivable land affected by salinity and nearly half regularly inundated, and salinity intrusion is expected to worsen under climate change. The country faces an acute shortage of quality fodder, and livestock diets depend heavily on crop residues and roadside grasses that are high in fiber but low in essential nutrients. Pakchong, with a reported yield potential of up to 500 tons per hectare per year and crude protein levels of 16 to 18 percent under favorable management, is one of the most promising forages for such feed-deficient areas. At the same time, excessive reliance on urea carries environmental costs, including nutrient leaching, water contamination, and soil acidification, while sheep manure offers a locally available organic alternative that also supplies organic matter and improves soil structure. Longer-term, multi-season trials will be needed to confirm whether the benefits documented here persist.

Subject of Research: Integrated urea and sheep manure nitrogen management for Pakchong forage growth and quality in coastal Bangladesh

Article Title: Growth and forage quality response of pakchong (pennisetum purpureum × pennisetum americanum) to integrated urea and sheep manure nitrogen management in coastal bangladesh

Article References: Hasin, P., Fariha, S., Hassan, S., Labeba, P., Islam, S. S., & Islam, M. S. (2026). Growth and forage quality response of pakchong (pennisetum purpureum × pennisetum americanum) to integrated urea and sheep manure nitrogen management in coastal bangladesh. Discover Life, 56(1), Article 32. https://doi.org/10.1007/s11084-026-09749-1

Image Credits: AI Generated

DOI: 10.1007/s11084-026-09749-1

Keywords: Pakchong forage, sheep manure, urea, nitrogen management, coastal Bangladesh, forage quality, crude protein, dry matter, sustainable agriculture, Khulna University, Napier hybrid grass, fertilizer substitution