Results of the second five-year period of an intensive production schedule of four vegetable crops for processing. II.

The inuence of herbicides and fertilizers on soil fertility recorded during the second ve-year segment of a long term vegetable cropping sequence carried out in Southern Italy and the ten-year balance (I976-I985) of N, P, and K in the soil are reported. Annually, beginning in September I980, through September I985, the four vegetable crops grown were: broccoli, spinach, pickling cucumbers, and snap beans. With the exception of l98l, when snap beans preceded pickling cucumbers, the sequence followed was: broccoli, spinach, pickling cucumbers, and snap beans. Three herbicides and no herbicide treatments and twelve different fertilizer treatments were applied to each crop. Each year, after harvest of the last crop and before ploughing in its residues, soil samples were obtained and analyzed for organic matter, N, P, K, and other soil characteristics. Samples taken included soil from the surface to the depth of 35 cm; at the end of the tenth year of the experiment, deeper (35-70 cm) soil samples were taken from selected subplots. A balance sheet format for soil OM, N, P, and K was developed using data recorded from NOPOKO, N|P|K|, and N;P;K2 subplots of no herbicide mainplots. Soil organic matter resulted lower in soil treated with herbicides tlmn 'llI~ l ..-Z, differences resulted larger when richer fertilizer rates were applied. Total nitrogen level resulted slightly higher Ill soil treated with fertilizer treatments including nitrogen. Soil treated with herbicides accumulated more available phosphorous and organic matter than untreated soil whereas exchangeable potassium showed an opposite behaviour. Some herbicide treatments effected the accumulation in the soil of nitrogen, organic matter, potassium, and phosphorous. Over years, both soil available phosphorous and exchangeable potassium levels continued to increase according to the fertilizer rates applied. Soil pl-I decreased during the years and with the richer fertilizer rates. Soil electrical conductivity increased with increased fertilizer application, although annual rainfall also inuenced values recorded which were higher in drier years. After ten years, of fertilizer application, anions and cations extracted from the soil by electro-ultrafiltration (EU F) conrmed the accumulation of the major nutrients applied and it showed a tremendous increase for C:13 * and SO} " as well. Elemental balances showed that each year S5 to 75 t ha' ' of fresh crop residues were decomposed in the soil, which resulted in a poor addition to the organic matter accumulation in fertilized soil. Unfertilized soil was able to provide nitrogen and phosphorous to the crops and it resulted enriched by nitrogen and total phosphorous at the end of the tenth year of the cropping sequence while no accumulation of available phosphorous and exchangeable potassium was observed. ln any case, soil nitrogen accumulation was very low while nitrogen losses were very high (up to 4?."/0 of nitrogen applied); both total and available phosphorous and exchangeable potassium accumulated. The lower soil layer appeared to gain part of the nitrogen and most of potassium losses recorded in the upper layer; the lower soil layer, instead, was impoverished by phosphorous uptake by roots which partly accumulated in the upper layer.