Műtrágyázás hatása a lucerna (Medicago sativa L.) fejlődésére és termésére karbonátos homoktalajon | Effect of fertilisation on the development and yield of alfalfa (Medicago sativa L.) on calcareous sandy soil

Summary We examined the effect of treatments on the development, weed occurance and hay yield of alfalfa, as well as the AL-soluble PK content of the ploughed layer of soil between 2000–2001, in the 31st–34th years of our long-term NPK fertilisation experiment established in the Danube-Tisza mid-region on calcareous sandy soil in 1970. The soil of the production site contains about 1% of CaCO ₃ and humus and the ploughed layer contains 5–10% clay. The soil under the ploughed layer is strongly calcareous. The groundwater is at a depth of 5–7 m, the area is drought-sensitive and the production site is weakly supplied with the main nutrients (N, P, K). The main conclusions which can be drawn from the experiment are as follows: Where the soil has not been fertilised for 29 years, its AL-soluble PK content was low. However, the AL-PK content was 150–200 mg kg –¹ AL-P ₂O ₅ and AL-K ₂O (on a “satisfactory” level or beyond) owing to the PK fertilisation enriching the soil. Alfalfa emerged slowly in the spring of 2001 on unfertilised control soil, it remained underdeveloped and short with light green colour. NP treatments resulted in average shooting, height and strong green colour, whereas the abundant NPK fertilisation resulted in strongly shooting, thick, developed, ivy green population. As a result of the subsequent mowings, the population of both the control and NP plots gradually became sparse, they became underdeveloped and overgrown with weeds. In the spring of 2004, the fourth year, alfalfa practically died out in the K-control NP treatments, the weed coverage was higher by magnitudes. The coverage of weeds and alfalfa on the absolute control soil was nearly the same. As a result of abundant K fertilisation (N ₂P ₂K ₄ treatments), the coverage of alfalfa was higher than that of weeds by magnitudes and the total plant coverage was higher than 80%, whereas the number of weed species dropped to half. As for the hay yields of the examined years (eight mowings), we obtained 6.8 t ha –¹ in the control plots, 8.4 t ha –¹ in the N1P1 treatments, 9.5 t ha –¹ in the N ₂P ₂ treatment and 12.5 t ha –¹ in the N ₂P ₂K ₄ treatments. The yield surpluses of the NP treatments were obtained in the first two years. For the 3rd and 4th years, the available K pool of the non-fertilised soil/subsoil was exhausted, therefore it became partially infertile for alfalfa. On the soil with extreme K shortage (NP treatments), we observed the following coverage data: Field chickweed (CER AR): 18%, Smooth brome (BRO IN): 4–6%, Cassweed (CAP BU): 2%, weeds: 24–29%, alfalfa: 2–4%. In the experiment, we identified 18 weed species in 2000 and 27 in 2004. In the spring of 2000, the prevailing species were dicotyledonous (Amaranthus spp.) after winter barley as a green crop, where monocotyledonous species were dominant in 2004.