Effect of preceding crops and green manure on the fertility of clay loam soil
Joniskelis Research Station of the Lithuanian Institute of Agriculture, Joniskelis, LT-5240 Pasvalys District, Lithuania; tel.fax.: 370-71-38224; e-mail: email@example.com
Influence of red clover (Trifolium pratense L.), sown lucerne (Medicago sativa L.), vetch and oat mixture (Vicia sativa L., Avena sativa L.) and green material of these legume crops used as green manure on the build up of biological N variation of soil properties and productivity of winter wheat (Triticum aestivum L.) was investigated on Endocalcari-Endohypogleyic Cambisol (CMg-n-w-can), according to the texture – clay loam on silty clay. Experiments were carried out at the Joniskelis Research Station of the Lithuanian Institute of Agriculture over the period 1996–2000. It was revealed that lucerne and clover left the highest content of plant residues in the soil (13.7 t ha-1 and 9.2 t ha-1 of dry matter, respectively) which was 2.7 and 1.8 times more as compared to annual vetch and oat mixture. These perennial plants also determined accumulation of the highest content of biological N in roots and residues. According to N content applied with green manure, only lucerne aftermath was comparable to farmyard manure. Lucerne determined accumulation of the highest contents of total nitrogen (0.138%), humus (2.18%) and available phosphorus and potassium (130 and 279 mg kg-1 of soil, respectively) in the soil. Analysis of humus composition showed that its content in clay loam soil was rather stable, however, a slightly higher content of mobile humic acids was found after lucerne as a preceding crop when green manure or farmyard manure had been applied. When winter wheat was grown after lucerne as a preceding crop, the highest grain yield (on average 5.58 t ha-1) was obtained, which was 18.5 and 28.3% higher than that after clover or vetch and oat mixture. Protein content in winter wheat grain was to a greater extent determined by legume crops rather than organic manure.