The paper describes the influence of long-term (more than 30 years) fertilizer and lime application on the soil acidity (pH Cl ) and identifies the influence of soil acidity on the productivity of crops. Since 1994, a seven-year crop rotation was created: (1) winter triticale → (2) potatoes → (3) spring wheat → (4) spring oilseed rape → (5) spring barley → (6) and (7) perennial grasses (red clover, timothy), 1 st and 2 nd year of use. At the beginning of the experiment, the soil in treatments F0 and F2 was very strongly acid (pH KCl 4.7) but in treatments F1 and F3 -moderately acid (pH KCl 5.6). In limed treatments the soil acidity decreased from pH 4.8 to pH 5.8-6.0. In the following years till 1994, the soil acidity in limed treatments gradually increased (for about 0.4-0.6 pH units). After the first maintenance liming, the soil acidity reached nearly the previous highest level. Within the next twenty years, in the treatments with highest liming rate (11.40 t ha -1 CaCO 3 ) the soil acidity increased to pH 5.2. In treatments with low liming rate (2.58 t ha -1 CaCO 3 ), the soil acidity increased to pH 4.6, which was even lower than at the beginning of the experiment (pH 4.8). Without maintenance liming, the soil acidity during 20 years increased by 0.7-0.8 pH units. In the unlimed treatments, the soil acidity gradually increased from pH 4.8 to 4.4.

The temperature distribution inside the experimental greenhouse heated by air to air heat pumps and its impact on the growth and productivity of tomato plants were studied. Experimental greenhouse located at SIA Rītausma facility in South-East Latvia.Two commercially available regular air to air heat‑pumps with a combined heat power of 10 kW were used. To measure the temperature distribution, 18 temperature sensors with solar radiation shields at different heights and positions among the plants were installed. Additional 4 temperature sensors were used to measure the air flow temperature at the heating elements. Reference air temperature was measured at an industrial production facility heated by a common gas heating system.Temperature was found to be homogenous within 1 °C. Observed temperatures were up to 4 °C lower than set on the control unit of the heat pump. This discrepancy was compensated by higher set values for the controlling unit. As research showed the temperature stability was better than at the water-heated industrial facility at time slots when the sun was suddenly cleared from clouds.The cooling of the experimental greenhouse by air conditioning during summer time was rather challenging for the tomato plants and productivity. 23% of plant stems died until the end of the season and the yield was 50% lower than in the reference greenhouse. The energy efficiency compared to the industrial facility was approx. 8 times better and the estimated CO2 emissions were 8-16 times smaller compared to gas heating. There were no increases of heating costs determined.Further studies are needed to optimize the heating parameters and reach the desired greenhouse productivity.

<p>The paper describes the influence of long term (more than 30 years) fertilizer application to the changes of soil properties and identifies the influence of different fertilization rates to phosphorus, potassium, calcium and magnesium accumulation in soil.</p><p>The research has been carried out at the Research Institute of Agriculture of Latvian University of Agriculture in the long-term subsurface drainage field established in Skrīveri in 1981 under the guidance of professor J. Štikāns.  The long-term drainage field was established in the uncultivated gleyic sod-podzolic <em>Hypostagnic</em> <em>Endogleyic Albeluvisol (Hypereutric), stw-ng-AB(he) </em>loam that had not been used in agriculture for 20 years before. The experimental field was established with four rates of mineral fertilizers: without fertilizers, N45P30K45; N90P60K90 N135P90K135 calculated in form of P₂O₅ and K₂O. Since 1994 a seven-year crop rotation has been organized: 1) winter triticale, 2) potatoes, 3) spring wheat, 4) spring oilseed rape, 5) spring barley + perennial grasses (red clover, timothy), 6) perennial grasses, 1st year of using, and 7) perennial grasses 2nd year of using. Mineral fertilizers were applied according to the anticipated rates of plant nutrient elements annually during the cultivation of soil before sowing. For winter cultivars the phosphorus as superphosphate and potassium as potassium chloride fertilizers were cultivated before the sowing in autumn and nitrogen in form of ammonium nitrate was applied the next spring at the beginning of vegetation and at the stage of tillering. During the vegetation period all the required common agro-technical measures were taken – treatment with herbicides, fungicides and insecticides.</p><p>After 32 years of trial similar soil parameters showed significantly different content of nutrients related to the different level of fertilizer application. On a low background of fertilizers (N45P30K45) a small increase of mobile phosphorus in soil has only been observed in recent years. At the fertilizer rate N90P60K90 the content of available phosphorus and potassium in soil gradually begins to grow. Fertilization norm N135P90K135 caused a constant accumulation of nutrients in soil. In 30 years’ time the content of exchangeable phosphorus (calcium lactate – extractable) has increased more than 20 times (from 9 till 184 mg P₂O₅ kg^-1) and exchangeable potassium (calcium lactate – extractable) has increased more than 4 times (from 64 till 223 mg K₂O kg^-1). There were no relation between different fertilizing rates and calcium and magnesium content in soil observed.</p><p> </p>

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Slāpekļa N iznese ar graudiem un salmiem slāpekļa mēslojuma ietekmē. 3.51. att. N iznese ar graudiem un salmiem pēc dažādiem priekšaugiem, kg ha-1 N. 3.52. att. Slāpekļa bilance vasaras kviešos mālsmilts augsnē, N kg ha-1. 3.53. att. Slāpekļa bilance vasaras kviešos smilšmāla augsnē, N kg ha-1. 3.54. att. Optimālo graudu ražu atšķirības pēc dažādiem priekšaugiem, t ha-1. 3.55. att. Optimālo slāpekļa mēslojuma normu atšķirības pēc dažādiem priekšaugiem. 3.56. att. Slāpekļa N bilance augsnē pielietojot slāpekļa diagnostikas un aprēķinu metodes, kg ha-1. TABULU SARAKSTS 1.1. tab. Augsnes dziļuma ietekme uz slāpekļa zudumu denitrifikācijas rezultātā 18 1.2. tab. Slāpekļa mēslojuma devas palielināšanas ietekme uz N izskalošanos 20 1.3. tab. Minerālmēslu slāpekļa sadalījums augsnē 29 2.1. tab. Slāpekļa mēslojuma varianti 1999.-2001. g. 48 2.2. tab. Slāpekļa mēslojuma otrā un kopējā deva diagnostikas variantā 49 2.3. tab. Augšņu agroķīmiskie rādītāji, vidēji 1999.-2001. g. (0-20 cm) 50 2.4. tab. Augšņu granulometriskais sastāvs, % 50