The effects of urine and urine-separated plant nutrient sources on growth and biomass production of perennial ryegrass (Lolium perenne. L)

Abstract

Urine contains plant essential nutrients, which may pose pollution problems if disposed of in the environment. Struvite is a concentrated phosphorus fertilizer produced by precipitation of Magnesium Ammonium Phosphate after addition of magnesium salts into urine. The struvite effluent has been shown to contain high concentrations of mineral elements such as nitrogen, which are important for plant growth. Urine can further be nitrified directly to produce a nutrient source with more of nitrate- N than ammonium- N. There is little information on use of these urine product for agriculture particularly in South Africa. The aim of this study was to determine the effect of urine and urine products, struvite (S), struvite effluent (S.E) and nitrified urine concentrate (NUC), on the growth and biomass production of perennial ryegrass. The specific objectives were (1) to determine nitrogen release pattern of urine and urine products (S, S.E and NUC) in two different soils (Cartref and Inanda soil), (2) to determine the effect of the application of urine and urine products on growth and biomass production of perennial ryegrass. A soil incubation experiment was set up under controlled room temperature at 25oC and 80% atmospheric humidity to determine nitrogen release pattern of urine and the urine products in two different soils. The experiment was designed as a 6 x 2 x 2 factorial treatment structure with five nutrient sources (urine, struvite effluent, struvite effluent + struvite, nitrified urine concentrate) and no fertilizer treatment as a control). The fertilizer materials were applied at two levels (recommended rates and double the recommended rates based on N rate). The two soil types used were the Inanda (acidic clay soil) and Cartref (sandy soil). The treatments were replicated three times giving 72 experimental units (in 2 kg ventilated containers). Data was collected on the ammonium and nitrate- N release on weekly basis for the period of 70 days. A pot trial was set up in 1 kg pots in the tunnel at 26oC air temperature and 65% atmospheric humidity to determine the effect of the application of urine and urine products on growth and biomass production of perennial ryegrass. The pot experiment was also designed as a 6 x 2 x 2 factorial treatment structure with six nutrient sources consisting of urine, struvite effluent, struvite effluent + struvite, nitrified urine concentrate and two controls; an inorganic fertilizer source (NPK 2:3:2) and no fertilizer treatment. The nutrient sources were either applied once off split applied three times. The fertilizer materials were applied at two levels (recommended rates and double the recommended rates) based on N rate. The treatment combinations were replicated three times. Plants were cut back to 5cm above the ground after attaining a cutting height of 20

cm height, and were allowed to regrow this was repeated four times. Soil moisture was maintained at 70-100% field capacity. The soil incubation experiment showed that there were significant (P<0.05) differences observed among treatments- U, S.E, S.E+S, NUC, NPK and Zero fertilizer, and among application rate. In Inanda soil, ammonium- N declined with incubation time while nitrate-N and mineral- N did not increase significantly. In the Catref soil ammonium- N declined with incubation time while nitrate- N and mineral- N increased significantly. The findings suggested that the Cartref soil released more nitrogen than Inanda soil hence it had more total mineral- N than Inanda soil Pot experiment result showed that there were significant (P<0.05) differences observed in dry matter production and plant height among the treatments, application method (once- off and split rate), application rates (recommended and double rate) and cuts (harvest), likewise in plant height. Dry matter production increased significantly with days after cuts- 1, 2 and 3 and it declined with time after cut 3 at cut 4. Split rate application method had significantly more dry matter than once- off application method. The recommended rate had significantly more dry matter than double rate. Treatment NUC responded significantly different within cuts. NUC treatment at recommended had significantly higher dry matter yield then all treatments at cut 1 and 3. At the same time there were no significant differences in dry matter production between NPK and urine and urine products. All treatments had however significantly higher dry matter than zero fertilizer treatment. The findings of the study suggested that urine and urine products are equally as effective as mineral fertilizer especially in sandy soil and that splitting the application is a useful strategy to manage urine and urine products for optimum dry matter production.