Rationale for Maintaining Humus in Arable Soils of Moldova

Abstract

A humus balance sheet was calculated for the 1,786 million ha of arable land in Moldova. Overall and under most crops, the humus balance is strongly negative. Only perennial herbs, especially when sown as mixtures with grasses, produce a large surplus of crop residues; they also contribute to the nitrogen balance. The current structure of cropping, with 68 % of arable under clean-weeded crops, viticulture and orchards, mineralizes 2,992 thousand tonnes of humus but returns only 718 thousand tonnes of crop residues – only one quarter of the necessary return of soil organic matter.

Various model cropping structures may be proposed to close the gap by reducing the area of clean-weeded crops and substituting perennial grasses and legumes in suitable areas, which could increase the input of humus by one third and, at the same time, reduce the mineralization of soil reserves. This would compensate for 60 % of the current humus deficit. Beyond this, perennial grasses and legumes used as fodder could increase the amount of manure to provide 4.6 t/ha/year, compensating for the remaining 40 % of the humus deficit. As well as achieving a balance of humus, the proposed modification of cropping patterns would provide an annual turnover of about 2,900 lei ($US242)/ha.